From b846a7a0ea77de85c0d84d3653d8db8d3c81b4c9 Mon Sep 17 00:00:00 2001 From: Přemysl Janouch Date: Sat, 24 Dec 2016 22:27:38 +0100 Subject: Add support for OpenBSD It just rejects the generic System V ABI and has other syscall numbers. --- Makefile | 8 +- README.adoc | 6 +- bfc-amd64-linux.c | 733 ----------------------------------------------------- bfc-amd64.c | 744 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 752 insertions(+), 739 deletions(-) delete mode 100644 bfc-amd64-linux.c create mode 100644 bfc-amd64.c diff --git a/Makefile b/Makefile index 5bb5db1..d25311c 100644 --- a/Makefile +++ b/Makefile @@ -1,11 +1,13 @@ # All we need is C99 and POSIX, which this should make available CFLAGS = -std=gnu99 -NAMES = bfc-amd64-linux +NAMES = bfc-amd64-linux bfc-amd64-openbsd all: $(NAMES) -%: %.c - $(CC) $(CPPFLAGS) $(CFLAGS) $< -o $@ +%-linux: %.c + $(CC) $(CPPFLAGS) $(CFLAGS) $< -o $@ -DTARGET_LINUX +%-openbsd: %.c + $(CC) $(CPPFLAGS) $(CFLAGS) $< -o $@ -DTARGET_OPENBSD clean: rm -f $(NAMES) diff --git a/README.adoc b/README.adoc index e04e8bd..69ebd7e 100644 --- a/README.adoc +++ b/README.adoc @@ -1,8 +1,8 @@ bfc === -'bfc' is a small, fast, self-contained, optimizing Brainfuck compiler for Linux -on Intel x86-64. +'bfc' is a small, fast, self-contained, optimizing Brainfuck compiler for *nix +on Intel x86-64. Currently supported targets are Linux and OpenBSD. Also included are several interpreters in various states of sophistication that document my progress as I was writing this, from the simplest approach to an @@ -14,7 +14,7 @@ The compiler itself is platform agnostic. Building -------- Build dependencies: a C99 compiler + -Runtime dependencies: Linux +Runtime dependencies: Linux or OpenBSD $ git clone https://github.com/pjanouch/bfc.git $ cd bfc diff --git a/bfc-amd64-linux.c b/bfc-amd64-linux.c deleted file mode 100644 index 1579681..0000000 --- a/bfc-amd64-linux.c +++ /dev/null @@ -1,733 +0,0 @@ -// This is an exercise in futility more than anything else -#include -#include -#include -#include -#include -#include -#include - -#ifdef __unix__ -#include -#endif - -#define exit_fatal(...) \ - do { \ - fprintf (stderr, "fatal: " __VA_ARGS__); \ - exit (EXIT_FAILURE); \ - } while (0) - -// --- Safe memory management -------------------------------------------------- - -static void * -xcalloc (size_t m, size_t n) -{ - void *p = calloc (m, n); - if (!p) - exit_fatal ("calloc: %s\n", strerror (errno)); - return p; -} - -static void * -xrealloc (void *o, size_t n) -{ - void *p = realloc (o, n); - if (!p && n) - exit_fatal ("realloc: %s\n", strerror (errno)); - return p; -} - -// --- Dynamically allocated strings ------------------------------------------- - -struct str -{ - char *str; ///< String data, null terminated - size_t alloc; ///< How many bytes are allocated - size_t len; ///< How long the string actually is -}; - -static void -str_init (struct str *self) -{ - self->len = 0; - self->str = xcalloc (1, (self->alloc = 16)); -} - -static void -str_ensure_space (struct str *self, size_t n) -{ - // We allocate at least one more byte for the terminating null character - size_t new_alloc = self->alloc; - while (new_alloc <= self->len + n) - new_alloc <<= 1; - if (new_alloc != self->alloc) - self->str = xrealloc (self->str, (self->alloc = new_alloc)); -} - -static void -str_append_data (struct str *self, const void *data, size_t n) -{ - str_ensure_space (self, n); - memcpy (self->str + self->len, data, n); - self->str[self->len += n] = '\0'; -} - -static void -str_append_c (struct str *self, char c) -{ - str_append_data (self, &c, 1); -} - -// --- Application ------------------------------------------------------------- - -enum command -{ - RIGHT, LEFT, INC, DEC, IN, OUT, BEGIN, END, - SET, EAT, INCACC, DECACC -}; - -bool grouped[] = { 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 }; -struct instruction { enum command cmd; int offset; size_t arg; }; -#define INSTRUCTION(c, o, a) (struct instruction) { (c), (o), (a) } - -// - - Debugging - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -#ifdef DEBUG -static void -debug_dump_instruction (FILE *fp, const struct instruction *in) -{ - const char *name; - switch (in->cmd) - { - case RIGHT: name = "RIGHT "; break; - case LEFT: name = "LEFT "; break; - case INC: name = "INC "; break; - case DEC: name = "DEC "; break; - case OUT: name = "OUT "; break; - case IN: name = "IN "; break; - case BEGIN: name = "BEGIN "; break; - case END: name = "END "; break; - case SET: name = "SET "; break; - case EAT: name = "EAT "; break; - case INCACC: name = "INCACC"; break; - case DECACC: name = "DECACC"; break; - } - fprintf (fp, "%s %zu", name, in->arg); - if (in->offset != 0) - fprintf (fp, " [%d]", in->offset); - fprintf (fp, "\n"); -} - -static void -debug_dump (const char *filename, struct instruction *in, size_t len) -{ - FILE *fp = fopen (filename, "w"); - long indent = 0; - for (size_t i = 0; i < len; i++) - { - if (in[i].cmd == END) - indent--; - for (long k = 0; k < indent; k++) - fputs (" ", fp); - debug_dump_instruction (fp, &in[i]); - if (in[i].cmd == BEGIN) - indent++; - } - fclose (fp); -} -#else -#define debug_dump(...) -#endif - -// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - - - -static size_t -optimize_assignment (struct instruction *irb, size_t irb_len) -{ - size_t in = 0, out = 0; - for (; in < irb_len; in++, out++) - { - if (in + 2 < irb_len - && irb[in ].cmd == BEGIN - && irb[in + 1].cmd == DEC && irb[in + 1].arg == 1 - && irb[in + 2].cmd == END) - { - irb[out] = INSTRUCTION (SET, 0, 0); - in += 2; - } - else if (out && irb[out - 1].cmd == SET && irb[in].cmd == INC) - irb[--out].arg += irb[in].arg; - else if (out != in) - irb[out] = irb[in]; - } - return out; -} - -// Add the offset of the LEFT/RIGHT instruction to the accumulator -static bool -add_direction_offset (struct instruction *irb, intptr_t *acc) -{ - if (irb->cmd == RIGHT) - *acc += irb->arg; - else if (irb->cmd == LEFT) - *acc -= (intptr_t) irb->arg; - else - return false; - return true; -} - -// Add offsets to INC/DEC/SET stuck between LEFT/RIGHT -// and compress the LEFT/RIGHT sequences -static size_t -optimize_offseted_inc_dec (struct instruction *irb, size_t irb_len) -{ - size_t in = 0, out = 0; - for (in = 0, out = 0; in < irb_len; in++, out++) - { - intptr_t dir = 0; - if (!add_direction_offset (&irb[in], &dir)) - { - irb[out] = irb[in]; - continue; - } - - while (in + 2 < irb_len) - { - // An immediate offset has its limits on x86-64 - if (dir < INT8_MIN || dir > INT8_MAX) - break; - intptr_t diff = 0; - if (!add_direction_offset (&irb[in + 2], &diff)) - break; - int cmd = irb[in + 1].cmd; - if (cmd != INC && cmd != DEC && cmd != SET) - break; - - irb[out] = irb[in + 1]; - irb[out].offset = dir; - - dir += diff; - out += 1; - in += 2; - } - - for (; in + 1 < irb_len; in++) - if (!add_direction_offset (&irb[in + 1], &dir)) - break; - - if (!dir) - out--; - else if (dir > 0) - irb[out] = INSTRUCTION (RIGHT, 0, dir); - else - irb[out] = INSTRUCTION (LEFT, 0, -dir); - } - return out; -} - -// Try to eliminate loops that eat a cell and add/subtract its value -// to/from some other cell -static size_t -optimize_inc_dec_loops (struct instruction *irb, size_t irb_len) -{ - size_t in = 0, out = 0; - for (in = 0, out = 0; in < irb_len; in++, out++) - { - irb[out] = irb[in]; - if (irb[in].cmd != BEGIN) - continue; - - bool ok = false; - size_t count = 0; - for (size_t k = in + 1; k < irb_len; k++) - { - if (irb[k].cmd == END) - { - ok = true; - break; - } - if (irb[k].cmd != INC - && irb[k].cmd != DEC) - break; - count++; - } - if (!ok) - continue; - - // Stable sort operations by their offsets, put [0] first - bool sorted; - do - { - sorted = true; - for (size_t k = 1; k < count; k++) - { - if (irb[in + k].offset == 0) - continue; - if (irb[in + k + 1].offset != 0 - && irb[in + k].offset <= irb[in + k + 1].offset) - continue; - - struct instruction tmp = irb[in + k + 1]; - irb[in + k + 1] = irb[in + k]; - irb[in + k] = tmp; - sorted = false; - } - } - while (!sorted); - - // Abort the optimization on duplicate offsets (complication with [0]) - for (size_t k = 1; k < count; k++) - if (irb[in + k].offset == irb[in + k + 1].offset) - ok = false; - // XXX: can't make the code longer either - for (size_t k = 1; k <= count; k++) - if (irb[in + k].arg != 1) - ok = false; - if (!ok - || irb[in + 1].cmd != DEC - || irb[in + 1].offset != 0) - continue; - - int min_safe_left_offset = 0; - if (in > 1 && irb[in - 1].cmd == RIGHT) - min_safe_left_offset = -irb[in - 1].arg; - - bool cond_needed_for_safety = false; - for (size_t k = 0; k < count; k++) - if (irb[in + k + 1].offset < min_safe_left_offset) - { - cond_needed_for_safety = true; - break; - } - - in++; - if (cond_needed_for_safety) - out++; - - irb[out] = INSTRUCTION (EAT, 0, 0); - for (size_t k = 1; k < count; k++) - irb[out + k] = INSTRUCTION (irb[in + k].cmd == INC - ? INCACC : DECACC, irb[in + k].offset, 0); - - in += count; - out += count; - - if (cond_needed_for_safety) - irb[out] = INSTRUCTION (END, 0, 0); - else - out--; - } - return out; -} - -// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -static void -pair_loops (struct instruction *irb, size_t irb_len) -{ - size_t nesting = 0; - size_t *stack = xcalloc (sizeof *stack, irb_len); - for (size_t i = 0; i < irb_len; i++) - { - switch (irb[i].cmd) - { - case BEGIN: - stack[nesting++] = i; - break; - case END: - if (nesting <= 0) - exit_fatal ("unbalanced loops\n"); - - --nesting; - irb[stack[nesting]].arg = i + 1; - - // Looping can be disabled by optimizations - if (irb[i].arg) - irb[i].arg = stack[nesting] + 1; - default: - break; - } - } - free (stack); - - if (nesting != 0) - exit_fatal ("unbalanced loops\n"); -} - -// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -int -main (int argc, char *argv[]) -{ - if (argc > 3) - exit_fatal ("usage: %s [INPUT-FILE] [OUTPUT-FILE]\n", argv[0]); - - FILE *input_file = stdin; - if (argc > 1 && !(input_file = fopen (argv[1], "r"))) - exit_fatal ("fopen: %s: %s\n", argv[1], strerror (errno)); - - const char *output_path = "a.out"; - if (argc > 2) - output_path = argv[2]; - - struct str buffer; - str_init (&buffer); - - int c; - while ((c = fgetc (input_file)) != EOF) - str_append_c (&buffer, c); - if (ferror (input_file)) - exit_fatal ("can't read program\n"); - fclose (input_file); - -// - - Decode, group and optimize - - - - - - - - - - - - - - - - - - - - - - - - - // This is our Intermediate Representation Buffer - struct instruction *irb = xcalloc (sizeof *irb, buffer.len); - size_t irb_len = 0; - - for (size_t i = 0; i < buffer.len; i++) - { - enum command cmd; - switch (buffer.str[i]) - { - case '>': cmd = RIGHT; break; - case '<': cmd = LEFT; break; - case '+': cmd = INC; break; - case '-': cmd = DEC; break; - case '.': cmd = OUT; break; - case ',': cmd = IN; break; - case '[': cmd = BEGIN; break; - case ']': cmd = END; break; - default: continue; - } - - // The most basic optimization is to group identical commands together - if (!irb_len || !grouped[cmd] || irb[irb_len - 1].cmd != cmd) - irb_len++; - - irb[irb_len - 1].cmd = cmd; - irb[irb_len - 1].arg++; - } - - debug_dump ("bf-no-opt.txt", irb, irb_len); - irb_len = optimize_assignment (irb, irb_len); - debug_dump ("bf-pre-offsets.txt", irb, irb_len); - irb_len = optimize_offseted_inc_dec (irb, irb_len); - debug_dump ("bf-pre-incdec-unloop.txt", irb, irb_len); - irb_len = optimize_inc_dec_loops (irb, irb_len); - debug_dump ("bf-optimized.txt", irb, irb_len); - pair_loops (irb, irb_len); - debug_dump ("bf-final.txt", irb, irb_len); - -// - - Code generation - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - str_init (&buffer); - size_t *offsets = xcalloc (sizeof *offsets, irb_len + 1); - bool *sets_flags = xcalloc (sizeof *sets_flags, irb_len); - -#define CODE(x) { char t[] = x; str_append_data (&buffer, t, sizeof t - 1); } -#define LE(v) (uint8_t[]) { v, v>>8, v>>16, v>>24, v>>32, v>>40, v>>48, v>>56 } -#define DB(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 1); } -#define DW(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 2); } -#define DD(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 4); } -#define DQ(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 8); } - - enum - { - ELF_LOAD_CODE = 0x400000, // where code is loaded (usual) - ELF_LOAD_DATA = 0x800000 // where the tape is placed - }; - - CODE ("\xB8") DD (ELF_LOAD_DATA) // mov rax, "ELF_LOAD_DATA" - CODE ("\x30\xDB") // xor bl, bl - - for (size_t i = 0; i < irb_len; i++) - { - offsets[i] = buffer.len; - - size_t arg = irb[i].arg; - assert (arg <= UINT32_MAX); - - int offset = irb[i].offset; - assert (offset <= INT8_MAX && offset >= INT8_MIN); - - // Don't save what we've just loaded - if (irb[i].cmd == LEFT || irb[i].cmd == RIGHT) - if (i < 2 || i + 1 >= irb_len - || (irb[i - 2].cmd != LEFT && irb[i - 2].cmd != RIGHT) - || irb[i - 1].cmd != BEGIN - || irb[i + 1].cmd != END) - CODE ("\x88\x18") // mov [rax], bl - - switch (irb[i].cmd) - { - case RIGHT: - // add rax, "arg" -- optimistic, no boundary checking - if (arg > INT8_MAX) { CODE ("\x48\x05") DD (arg) } - else { CODE ("\x48\x83\xC0") DB (arg) } - break; - case LEFT: - // sub rax, "arg" -- optimistic, no boundary checking - if (arg > INT8_MAX) { CODE ("\x48\x2D") DD (arg) } - else { CODE ("\x48\x83\xE8") DB (arg) } - break; - - case EAT: - // NOTE: the kernel destroys rcx and r11 on syscalls, - // there must be no OUT or IN between EAT and INCACC/DECACC - CODE ("\x88\xD9" "\x30\xDB") // mov cl, bl; xor bl, bl - sets_flags[i] = true; - break; - case INCACC: - if (offset) - { - CODE ("\x00\x48") DB (offset) // add [rax+"offset"], cl - } - else - { - CODE ("\x00\xCB") // add bl, cl - sets_flags[i] = true; - } - break; - case DECACC: - if (offset) - { - CODE ("\x28\x48") DB (offset) // sub [rax+"offset"], cl - } - else - { - CODE ("\x28\xCB") // sub bl, cl - sets_flags[i] = true; - } - break; - - case INC: - if (offset) - { - CODE ("\x80\x40") DB (offset) // add byte [rax+"offset"], "arg" - } - else - { - CODE ("\x80\xC3") // add bl, "arg" - sets_flags[i] = true; - } - DB (arg) - break; - case DEC: - if (offset) - { - CODE ("\x80\x68") DB (offset) // sub byte [rax+"offset"], "arg" - } - else - { - CODE ("\x80\xEB") // sub bl, "arg" - sets_flags[i] = true; - } - DB (arg) - break; - case SET: - if (offset) - { - CODE ("\xC6\x40") DB (offset) // mov byte [rax+"offset"], "arg" - } - else - CODE ("\xB3") // mov bl, "arg" - DB (arg) - break; - - case OUT: - CODE ("\xE8") DD (0) // call "write" - break; - case IN: - CODE ("\xE8") DD (0) // call "read" - break; - - case BEGIN: - // Don't test the register when the flag has been set already; - // this doesn't have much of an effect in practice - if (!i || !sets_flags[i - 1]) - CODE ("\x84\xDB") // test bl, bl - CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[arg]" - break; - case END: - // We know that the cell is zero, make this an "if", not a "loop"; - // this doesn't have much of an effect in practice - if (!arg) - break; - - if (!i || !sets_flags[i - 1]) - CODE ("\x84\xDB") // test bl, bl - CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[arg]" - break; - } - - // No sense in reading it out when we overwrite it immediately; - // this doesn't have much of an effect in practice - if (irb[i].cmd == LEFT || irb[i].cmd == RIGHT) - if (i + 1 >= irb_len - || irb[i + 1].cmd != SET - || irb[i + 1].offset != 0) - CODE ("\x8A\x18") // mov bl, [rax] - } - // When there is a loop at the end we need to be able to jump past it - offsets[irb_len] = buffer.len; - - // Write an epilog which handles all the OS interfacing - // - // System V x86-64 ABI: - // rax <-> both syscall number and return value - // args -> rdi, rsi, rdx, r10, r8, r9 - // trashed <- rcx, r11 - - enum { SYS_READ = 0, SYS_WRITE = 1, SYS_EXIT = 60 }; - - CODE ("\xB8") DD (SYS_EXIT) // mov eax, 0x3c - CODE ("\x48\x31\xFF") // xor rdi, rdi - CODE ("\x0F\x05") // syscall - - size_t fatal_offset = buffer.len; - CODE ("\x48\x89\xF7") // mov rdi, rsi -- use the string in rsi - CODE ("\x30\xC0") // xor al, al -- look for the nil byte - CODE ("\x48\x31\xC9") // xor rcx, rcx - CODE ("\x48\xF7\xD1") // not rcx -- start from -1 - CODE ("\xFC" "\xF2\xAE") // cld; repne scasb -- decrement until found - CODE ("\x48\xF7\xD1") // not rcx - CODE ("\x48\x8D\x51\xFF") // lea rdx, [rcx-1] -- save length in rdx - CODE ("\xB8") DD (SYS_WRITE) // mov eax, "SYS_WRITE" - CODE ("\xBF") DD (2) // mov edi, "STDERR_FILENO" - CODE ("\x0F\x05") // syscall - - CODE ("\xB8") DD (SYS_EXIT) // mov eax, "SYS_EXIT" - CODE ("\xBF") DD (1) // mov edi, "EXIT_FAILURE" - CODE ("\x0F\x05") // syscall - - size_t read_offset = buffer.len; - CODE ("\x50") // push rax -- save tape position - CODE ("\xB8") DD (SYS_READ) // mov eax, "SYS_READ" - CODE ("\x48\x89\xC7") // mov rdi, rax -- STDIN_FILENO - CODE ("\x66\x6A\x00") // push word 0 -- the default value for EOF - CODE ("\x48\x89\xE6") // mov rsi, rsp -- the char starts at rsp - CODE ("\xBA") DD (1) // mov edx, 1 -- count - CODE ("\x0F\x05") // syscall - CODE ("\x66\x5B") // pop bx - - CODE ("\x48\x83\xF8\x00") // cmp rax, 0 - CODE ("\x48\x8D\x35") DD (4) // lea rsi, [rel read_message] - CODE ("\x7C") // jl "fatal_offset" -- write failure message - DB ((intptr_t) fatal_offset - (intptr_t) (buffer.len + 1)) - CODE ("\x58") // pop rax -- restore tape position - CODE ("\xC3") // ret - CODE ("fatal: read failed\n\0") - - size_t write_offset = buffer.len; - CODE ("\x50") // push rax -- save tape position - CODE ("\xB8") DD (SYS_WRITE) // mov eax, "SYS_WRITE" - CODE ("\x48\x89\xC7") // mov rdi, rax -- STDOUT_FILENO - CODE ("\x66\x53") // push bx - CODE ("\x48\x89\xE6") // mov rsi, rsp -- the char starts at rsp - CODE ("\xBA") DD (1) // mov edx, 1 -- count - CODE ("\x0F\x05") // syscall - CODE ("\x66\x5B") // pop bx - - CODE ("\x48\x83\xF8\x00") // cmp rax, 0 - CODE ("\x48\x8D\x35") DD (4) // lea rsi, [rel write_message] - CODE ("\x7C") // jl "fatal_offset" -- write failure message - DB ((intptr_t) fatal_offset - (intptr_t) (buffer.len + 1)) - CODE ("\x58") // pop rax -- restore tape position - CODE ("\xC3") // ret - CODE ("fatal: write failed\n\0") - - // Now that we know where each instruction is, fill in relative jumps - for (size_t i = 0; i < irb_len; i++) - { - if (!irb[i].arg) - continue; - - // This must accurately reflect the code generators - intptr_t target, fixup = offsets[i]; - if (irb[i].cmd == BEGIN || irb[i].cmd == END) - { - fixup += (i && sets_flags[i - 1]) ? 2 : 4; - target = offsets[irb[i].arg]; - } - else if (irb[i].cmd == IN) { fixup++; target = read_offset; } - else if (irb[i].cmd == OUT) { fixup++; target = write_offset; } - else continue; - - uint64_t v = target - (fixup + 4); - memcpy (buffer.str + fixup, LE (v), 4); - } - free (offsets); - free (sets_flags); - -// - - Output - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - // Now that we know how long the machine code is, we can write the header. - // Note that for PIE we would need to depend on the dynamic linker, so no. - // - // Recommended reading: - // http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html - // man 5 elf - - struct str code = buffer; - str_init (&buffer); - - enum - { - ELF_HEADER_SIZE = 64, // size of the ELF header - ELF_PROGRAM_ENTRY_SIZE = 56, // size of a program header - ELF_SECTION_ENTRY_SIZE = 64, // size of a section header - ELF_META_SIZE = ELF_HEADER_SIZE + 2 * ELF_PROGRAM_ENTRY_SIZE - }; - - // ELF header - CODE ("\x7F" "ELF\x02\x01\x01") // ELF, 64-bit, little endian, v1 - CODE ("\x00\x00" "\0\0\0\0\0\0\0") // Unix System V ABI, v0, padding - DW (2) DW (62) DD (1) // executable, x86-64, v1 - DQ (ELF_LOAD_CODE + ELF_META_SIZE) // entry point address - DQ (ELF_HEADER_SIZE) DQ (0) // program, section header offset - DD (0) // no processor-specific flags - DW (ELF_HEADER_SIZE) // ELF header size - DW (ELF_PROGRAM_ENTRY_SIZE) DW (2) // program hdr tbl entry size, count - DW (ELF_SECTION_ENTRY_SIZE) DW (0) // section hdr tbl entry size, count - DW (0) // no section index for strings - - // Program header for code - // The entry point address seems to require alignment, so map start of file - DD (1) DD (5) // PT_LOAD, PF_R | PF_X - DQ (0) // offset within the file - DQ (ELF_LOAD_CODE) // address in virtual memory - DQ (ELF_LOAD_CODE) // address in physical memory - DQ (ELF_META_SIZE + code.len) // length within the file - DQ (ELF_META_SIZE + code.len) // length within memory - DQ (4096) // segment alignment - - // Program header for the tape - DD (1) DD (6) // PT_LOAD, PF_R | PF_W - DQ (0) // offset within the file - DQ (ELF_LOAD_DATA) // address in virtual memory - DQ (ELF_LOAD_DATA) // address in physical memory - DQ (0) // length within the file - DQ (1 << 20) // one megabyte of memory - DQ (4096) // segment alignment - - // The section header table is optional and we don't need it for anything - - FILE *output_file; -#ifdef __unix__ - int output_fd; - if ((output_fd = open (output_path, O_CREAT | O_WRONLY, 0777)) < 0) - exit_fatal ("open: %s: %s\n", output_path, strerror (errno)); - if (!(output_file = fdopen (output_fd, "w"))) - exit_fatal ("fdopen: %s\n", strerror (errno)); -#else - if (!(output_file = fopen (output_path, "w"))) - exit_fatal ("fopen: %s: %s\n", output_path, strerror (errno)); -#endif - - fwrite (buffer.str, buffer.len, 1, output_file); - fwrite (code.str, code.len, 1, output_file); - fclose (output_file); - return 0; -} diff --git a/bfc-amd64.c b/bfc-amd64.c new file mode 100644 index 0000000..9681ca1 --- /dev/null +++ b/bfc-amd64.c @@ -0,0 +1,744 @@ +// This is an exercise in futility more than anything else +#include +#include +#include +#include +#include +#include +#include + +#ifdef __unix__ +#include +#endif + +#define exit_fatal(...) \ + do { \ + fprintf (stderr, "fatal: " __VA_ARGS__); \ + exit (EXIT_FAILURE); \ + } while (0) + +// --- Safe memory management -------------------------------------------------- + +static void * +xcalloc (size_t m, size_t n) +{ + void *p = calloc (m, n); + if (!p) + exit_fatal ("calloc: %s\n", strerror (errno)); + return p; +} + +static void * +xrealloc (void *o, size_t n) +{ + void *p = realloc (o, n); + if (!p && n) + exit_fatal ("realloc: %s\n", strerror (errno)); + return p; +} + +// --- Dynamically allocated strings ------------------------------------------- + +struct str +{ + char *str; ///< String data, null terminated + size_t alloc; ///< How many bytes are allocated + size_t len; ///< How long the string actually is +}; + +static void +str_init (struct str *self) +{ + self->len = 0; + self->str = xcalloc (1, (self->alloc = 16)); +} + +static void +str_ensure_space (struct str *self, size_t n) +{ + // We allocate at least one more byte for the terminating null character + size_t new_alloc = self->alloc; + while (new_alloc <= self->len + n) + new_alloc <<= 1; + if (new_alloc != self->alloc) + self->str = xrealloc (self->str, (self->alloc = new_alloc)); +} + +static void +str_append_data (struct str *self, const void *data, size_t n) +{ + str_ensure_space (self, n); + memcpy (self->str + self->len, data, n); + self->str[self->len += n] = '\0'; +} + +static void +str_append_c (struct str *self, char c) +{ + str_append_data (self, &c, 1); +} + +// --- Application ------------------------------------------------------------- + +enum command +{ + RIGHT, LEFT, INC, DEC, IN, OUT, BEGIN, END, + SET, EAT, INCACC, DECACC +}; + +bool grouped[] = { 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 }; +struct instruction { enum command cmd; int offset; size_t arg; }; +#define INSTRUCTION(c, o, a) (struct instruction) { (c), (o), (a) } + +// - - Debugging - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + +#ifdef DEBUG +static void +debug_dump_instruction (FILE *fp, const struct instruction *in) +{ + const char *name; + switch (in->cmd) + { + case RIGHT: name = "RIGHT "; break; + case LEFT: name = "LEFT "; break; + case INC: name = "INC "; break; + case DEC: name = "DEC "; break; + case OUT: name = "OUT "; break; + case IN: name = "IN "; break; + case BEGIN: name = "BEGIN "; break; + case END: name = "END "; break; + case SET: name = "SET "; break; + case EAT: name = "EAT "; break; + case INCACC: name = "INCACC"; break; + case DECACC: name = "DECACC"; break; + } + fprintf (fp, "%s %zu", name, in->arg); + if (in->offset != 0) + fprintf (fp, " [%d]", in->offset); + fprintf (fp, "\n"); +} + +static void +debug_dump (const char *filename, struct instruction *in, size_t len) +{ + FILE *fp = fopen (filename, "w"); + long indent = 0; + for (size_t i = 0; i < len; i++) + { + if (in[i].cmd == END) + indent--; + for (long k = 0; k < indent; k++) + fputs (" ", fp); + debug_dump_instruction (fp, &in[i]); + if (in[i].cmd == BEGIN) + indent++; + } + fclose (fp); +} +#else +#define debug_dump(...) +#endif + +// - - Optimization passes - - - - - - - - - - - - - - - - - - - - - - - - - - - + +static size_t +optimize_assignment (struct instruction *irb, size_t irb_len) +{ + size_t in = 0, out = 0; + for (; in < irb_len; in++, out++) + { + if (in + 2 < irb_len + && irb[in ].cmd == BEGIN + && irb[in + 1].cmd == DEC && irb[in + 1].arg == 1 + && irb[in + 2].cmd == END) + { + irb[out] = INSTRUCTION (SET, 0, 0); + in += 2; + } + else if (out && irb[out - 1].cmd == SET && irb[in].cmd == INC) + irb[--out].arg += irb[in].arg; + else if (out != in) + irb[out] = irb[in]; + } + return out; +} + +// Add the offset of the LEFT/RIGHT instruction to the accumulator +static bool +add_direction_offset (struct instruction *irb, intptr_t *acc) +{ + if (irb->cmd == RIGHT) + *acc += irb->arg; + else if (irb->cmd == LEFT) + *acc -= (intptr_t) irb->arg; + else + return false; + return true; +} + +// Add offsets to INC/DEC/SET stuck between LEFT/RIGHT +// and compress the LEFT/RIGHT sequences +static size_t +optimize_offseted_inc_dec (struct instruction *irb, size_t irb_len) +{ + size_t in = 0, out = 0; + for (in = 0, out = 0; in < irb_len; in++, out++) + { + intptr_t dir = 0; + if (!add_direction_offset (&irb[in], &dir)) + { + irb[out] = irb[in]; + continue; + } + + while (in + 2 < irb_len) + { + // An immediate offset has its limits on x86-64 + if (dir < INT8_MIN || dir > INT8_MAX) + break; + intptr_t diff = 0; + if (!add_direction_offset (&irb[in + 2], &diff)) + break; + int cmd = irb[in + 1].cmd; + if (cmd != INC && cmd != DEC && cmd != SET) + break; + + irb[out] = irb[in + 1]; + irb[out].offset = dir; + + dir += diff; + out += 1; + in += 2; + } + + for (; in + 1 < irb_len; in++) + if (!add_direction_offset (&irb[in + 1], &dir)) + break; + + if (!dir) + out--; + else if (dir > 0) + irb[out] = INSTRUCTION (RIGHT, 0, dir); + else + irb[out] = INSTRUCTION (LEFT, 0, -dir); + } + return out; +} + +// Try to eliminate loops that eat a cell and add/subtract its value +// to/from some other cell +static size_t +optimize_inc_dec_loops (struct instruction *irb, size_t irb_len) +{ + size_t in = 0, out = 0; + for (in = 0, out = 0; in < irb_len; in++, out++) + { + irb[out] = irb[in]; + if (irb[in].cmd != BEGIN) + continue; + + bool ok = false; + size_t count = 0; + for (size_t k = in + 1; k < irb_len; k++) + { + if (irb[k].cmd == END) + { + ok = true; + break; + } + if (irb[k].cmd != INC + && irb[k].cmd != DEC) + break; + count++; + } + if (!ok) + continue; + + // Stable sort operations by their offsets, put [0] first + bool sorted; + do + { + sorted = true; + for (size_t k = 1; k < count; k++) + { + if (irb[in + k].offset == 0) + continue; + if (irb[in + k + 1].offset != 0 + && irb[in + k].offset <= irb[in + k + 1].offset) + continue; + + struct instruction tmp = irb[in + k + 1]; + irb[in + k + 1] = irb[in + k]; + irb[in + k] = tmp; + sorted = false; + } + } + while (!sorted); + + // Abort the optimization on duplicate offsets (complication with [0]) + for (size_t k = 1; k < count; k++) + if (irb[in + k].offset == irb[in + k + 1].offset) + ok = false; + // XXX: can't make the code longer either + for (size_t k = 1; k <= count; k++) + if (irb[in + k].arg != 1) + ok = false; + if (!ok + || irb[in + 1].cmd != DEC + || irb[in + 1].offset != 0) + continue; + + int min_safe_left_offset = 0; + if (in > 1 && irb[in - 1].cmd == RIGHT) + min_safe_left_offset = -irb[in - 1].arg; + + bool cond_needed_for_safety = false; + for (size_t k = 0; k < count; k++) + if (irb[in + k + 1].offset < min_safe_left_offset) + { + cond_needed_for_safety = true; + break; + } + + in++; + if (cond_needed_for_safety) + out++; + + irb[out] = INSTRUCTION (EAT, 0, 0); + for (size_t k = 1; k < count; k++) + irb[out + k] = INSTRUCTION (irb[in + k].cmd == INC + ? INCACC : DECACC, irb[in + k].offset, 0); + + in += count; + out += count; + + if (cond_needed_for_safety) + irb[out] = INSTRUCTION (END, 0, 0); + else + out--; + } + return out; +} + +// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + +static void +pair_loops (struct instruction *irb, size_t irb_len) +{ + size_t nesting = 0; + size_t *stack = xcalloc (sizeof *stack, irb_len); + for (size_t i = 0; i < irb_len; i++) + { + switch (irb[i].cmd) + { + case BEGIN: + stack[nesting++] = i; + break; + case END: + if (nesting <= 0) + exit_fatal ("unbalanced loops\n"); + + --nesting; + irb[stack[nesting]].arg = i + 1; + + // Looping can be disabled by optimizations + if (irb[i].arg) + irb[i].arg = stack[nesting] + 1; + default: + break; + } + } + free (stack); + + if (nesting != 0) + exit_fatal ("unbalanced loops\n"); +} + +// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + +int +main (int argc, char *argv[]) +{ + if (argc > 3) + exit_fatal ("usage: %s [INPUT-FILE] [OUTPUT-FILE]\n", argv[0]); + + FILE *input_file = stdin; + if (argc > 1 && !(input_file = fopen (argv[1], "r"))) + exit_fatal ("fopen: %s: %s\n", argv[1], strerror (errno)); + + const char *output_path = "a.out"; + if (argc > 2) + output_path = argv[2]; + + struct str buffer; + str_init (&buffer); + + int c; + while ((c = fgetc (input_file)) != EOF) + str_append_c (&buffer, c); + if (ferror (input_file)) + exit_fatal ("can't read program\n"); + fclose (input_file); + +// - - Decode, group and optimize - - - - - - - - - - - - - - - - - - - - - - - + + // This is our Intermediate Representation Buffer + struct instruction *irb = xcalloc (sizeof *irb, buffer.len); + size_t irb_len = 0; + + for (size_t i = 0; i < buffer.len; i++) + { + enum command cmd; + switch (buffer.str[i]) + { + case '>': cmd = RIGHT; break; + case '<': cmd = LEFT; break; + case '+': cmd = INC; break; + case '-': cmd = DEC; break; + case '.': cmd = OUT; break; + case ',': cmd = IN; break; + case '[': cmd = BEGIN; break; + case ']': cmd = END; break; + default: continue; + } + + // The most basic optimization is to group identical commands together + if (!irb_len || !grouped[cmd] || irb[irb_len - 1].cmd != cmd) + irb_len++; + + irb[irb_len - 1].cmd = cmd; + irb[irb_len - 1].arg++; + } + + debug_dump ("bf-no-opt.txt", irb, irb_len); + irb_len = optimize_assignment (irb, irb_len); + debug_dump ("bf-pre-offsets.txt", irb, irb_len); + irb_len = optimize_offseted_inc_dec (irb, irb_len); + debug_dump ("bf-pre-incdec-unloop.txt", irb, irb_len); + irb_len = optimize_inc_dec_loops (irb, irb_len); + debug_dump ("bf-optimized.txt", irb, irb_len); + pair_loops (irb, irb_len); + debug_dump ("bf-final.txt", irb, irb_len); + +// - - Code generation - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + str_init (&buffer); + size_t *offsets = xcalloc (sizeof *offsets, irb_len + 1); + bool *sets_flags = xcalloc (sizeof *sets_flags, irb_len); + +#define CODE(x) { char t[] = x; str_append_data (&buffer, t, sizeof t - 1); } +#define LE(v) (uint8_t[]) { v, v>>8, v>>16, v>>24, v>>32, v>>40, v>>48, v>>56 } +#define DB(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 1); } +#define DW(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 2); } +#define DD(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 4); } +#define DQ(x) { uint64_t v = (x); str_append_data (&buffer, LE (v), 8); } + + enum + { + ELF_LOAD_CODE = 0x400000, // where code is loaded (usual) + ELF_LOAD_DATA = 0x800000 // where the tape is placed + }; + + CODE ("\xB8") DD (ELF_LOAD_DATA) // mov rax, "ELF_LOAD_DATA" + CODE ("\x30\xDB") // xor bl, bl + + for (size_t i = 0; i < irb_len; i++) + { + offsets[i] = buffer.len; + + size_t arg = irb[i].arg; + assert (arg <= UINT32_MAX); + + int offset = irb[i].offset; + assert (offset <= INT8_MAX && offset >= INT8_MIN); + + // Don't save what we've just loaded + if (irb[i].cmd == LEFT || irb[i].cmd == RIGHT) + if (i < 2 || i + 1 >= irb_len + || (irb[i - 2].cmd != LEFT && irb[i - 2].cmd != RIGHT) + || irb[i - 1].cmd != BEGIN + || irb[i + 1].cmd != END) + CODE ("\x88\x18") // mov [rax], bl + + switch (irb[i].cmd) + { + case RIGHT: + // add rax, "arg" -- optimistic, no boundary checking + if (arg > INT8_MAX) { CODE ("\x48\x05") DD (arg) } + else { CODE ("\x48\x83\xC0") DB (arg) } + break; + case LEFT: + // sub rax, "arg" -- optimistic, no boundary checking + if (arg > INT8_MAX) { CODE ("\x48\x2D") DD (arg) } + else { CODE ("\x48\x83\xE8") DB (arg) } + break; + + case EAT: + // NOTE: the kernel destroys rcx and r11 on syscalls, + // there must be no OUT or IN between EAT and INCACC/DECACC + CODE ("\x88\xD9" "\x30\xDB") // mov cl, bl; xor bl, bl + sets_flags[i] = true; + break; + case INCACC: + if (offset) + { + CODE ("\x00\x48") DB (offset) // add [rax+"offset"], cl + } + else + { + CODE ("\x00\xCB") // add bl, cl + sets_flags[i] = true; + } + break; + case DECACC: + if (offset) + { + CODE ("\x28\x48") DB (offset) // sub [rax+"offset"], cl + } + else + { + CODE ("\x28\xCB") // sub bl, cl + sets_flags[i] = true; + } + break; + + case INC: + if (offset) + { + CODE ("\x80\x40") DB (offset) // add byte [rax+"offset"], "arg" + } + else + { + CODE ("\x80\xC3") // add bl, "arg" + sets_flags[i] = true; + } + DB (arg) + break; + case DEC: + if (offset) + { + CODE ("\x80\x68") DB (offset) // sub byte [rax+"offset"], "arg" + } + else + { + CODE ("\x80\xEB") // sub bl, "arg" + sets_flags[i] = true; + } + DB (arg) + break; + case SET: + if (offset) + { + CODE ("\xC6\x40") DB (offset) // mov byte [rax+"offset"], "arg" + } + else + CODE ("\xB3") // mov bl, "arg" + DB (arg) + break; + + case OUT: + CODE ("\xE8") DD (0) // call "write" + break; + case IN: + CODE ("\xE8") DD (0) // call "read" + break; + + case BEGIN: + // Don't test the register when the flag has been set already; + // this doesn't have much of an effect in practice + if (!i || !sets_flags[i - 1]) + CODE ("\x84\xDB") // test bl, bl + CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[arg]" + break; + case END: + // We know that the cell is zero, make this an "if", not a "loop"; + // this doesn't have much of an effect in practice + if (!arg) + break; + + if (!i || !sets_flags[i - 1]) + CODE ("\x84\xDB") // test bl, bl + CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[arg]" + break; + } + + // No sense in reading it out when we overwrite it immediately; + // this doesn't have much of an effect in practice + if (irb[i].cmd == LEFT || irb[i].cmd == RIGHT) + if (i + 1 >= irb_len + || irb[i + 1].cmd != SET + || irb[i + 1].offset != 0) + CODE ("\x8A\x18") // mov bl, [rax] + } + // When there is a loop at the end we need to be able to jump past it + offsets[irb_len] = buffer.len; + + // Write an epilog which handles all the OS interfacing + // + // System V x86-64 ABI: + // rax <-> both syscall number and return value + // args -> rdi, rsi, rdx, r10, r8, r9 + // trashed <- rcx, r11 + +#ifdef TARGET_OPENBSD + enum { SYS_READ = 3, SYS_WRITE = 4, SYS_EXIT = 1 }; +#elif defined TARGET_LINUX + enum { SYS_READ = 0, SYS_WRITE = 1, SYS_EXIT = 60 }; +#else +#error Target not supported +#endif + + CODE ("\xB8") DD (SYS_EXIT) // mov eax, 0x3c + CODE ("\x48\x31\xFF") // xor rdi, rdi + CODE ("\x0F\x05") // syscall + + size_t fatal_offset = buffer.len; + CODE ("\x48\x89\xF7") // mov rdi, rsi -- use the string in rsi + CODE ("\x30\xC0") // xor al, al -- look for the nil byte + CODE ("\x48\x31\xC9") // xor rcx, rcx + CODE ("\x48\xF7\xD1") // not rcx -- start from -1 + CODE ("\xFC" "\xF2\xAE") // cld; repne scasb -- decrement until found + CODE ("\x48\xF7\xD1") // not rcx + CODE ("\x48\x8D\x51\xFF") // lea rdx, [rcx-1] -- save length in rdx + CODE ("\xB8") DD (SYS_WRITE) // mov eax, "SYS_WRITE" + CODE ("\xBF") DD (2) // mov edi, "STDERR_FILENO" + CODE ("\x0F\x05") // syscall + + CODE ("\xB8") DD (SYS_EXIT) // mov eax, "SYS_EXIT" + CODE ("\xBF") DD (1) // mov edi, "EXIT_FAILURE" + CODE ("\x0F\x05") // syscall + + size_t read_offset = buffer.len; + CODE ("\x50") // push rax -- save tape position + CODE ("\xB8") DD (SYS_READ) // mov eax, "SYS_READ" + CODE ("\xBF") DD (0) // mov edi, "STDIN_FILENO" + CODE ("\x66\x6A\x00") // push word 0 -- the default value for EOF + CODE ("\x48\x89\xE6") // mov rsi, rsp -- the char starts at rsp + CODE ("\xBA") DD (1) // mov edx, 1 -- count + CODE ("\x0F\x05") // syscall + CODE ("\x66\x5B") // pop bx + + CODE ("\x48\x83\xF8\x00") // cmp rax, 0 + CODE ("\x48\x8D\x35") DD (4) // lea rsi, [rel read_message] + CODE ("\x7C") // jl "fatal_offset" -- write failure message + DB ((intptr_t) fatal_offset - (intptr_t) (buffer.len + 1)) + CODE ("\x58") // pop rax -- restore tape position + CODE ("\xC3") // ret + CODE ("fatal: read failed\n\0") + + size_t write_offset = buffer.len; + CODE ("\x50") // push rax -- save tape position + CODE ("\xB8") DD (SYS_WRITE) // mov eax, "SYS_WRITE" + CODE ("\xBF") DD (1) // mov edi, "STDOUT_FILENO" + CODE ("\x66\x53") // push bx + CODE ("\x48\x89\xE6") // mov rsi, rsp -- the char starts at rsp + CODE ("\xBA") DD (1) // mov edx, 1 -- count + CODE ("\x0F\x05") // syscall + CODE ("\x66\x5B") // pop bx + + CODE ("\x48\x83\xF8\x00") // cmp rax, 0 + CODE ("\x48\x8D\x35") DD (4) // lea rsi, [rel write_message] + CODE ("\x7C") // jl "fatal_offset" -- write failure message + DB ((intptr_t) fatal_offset - (intptr_t) (buffer.len + 1)) + CODE ("\x58") // pop rax -- restore tape position + CODE ("\xC3") // ret + CODE ("fatal: write failed\n\0") + + // Now that we know where each instruction is, fill in relative jumps + for (size_t i = 0; i < irb_len; i++) + { + if (!irb[i].arg) + continue; + + // This must accurately reflect the code generators + intptr_t target, fixup = offsets[i]; + if (irb[i].cmd == BEGIN || irb[i].cmd == END) + { + fixup += (i && sets_flags[i - 1]) ? 2 : 4; + target = offsets[irb[i].arg]; + } + else if (irb[i].cmd == IN) { fixup++; target = read_offset; } + else if (irb[i].cmd == OUT) { fixup++; target = write_offset; } + else continue; + + uint64_t v = target - (fixup + 4); + memcpy (buffer.str + fixup, LE (v), 4); + } + free (offsets); + free (sets_flags); + +// - - Output - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + // Now that we know how long the machine code is, we can write the header. + // Note that for PIE we would need to depend on the dynamic linker, so no. + // + // Recommended reading: + // http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html + // man 5 elf + + struct str code = buffer; + str_init (&buffer); + + enum + { + ELF_HEADER_SIZE = 64, // size of the ELF header + ELF_PROGRAM_ENTRY_SIZE = 56, // size of a program header + ELF_SECTION_ENTRY_SIZE = 64, // size of a section header + ELF_META_SIZE = ELF_HEADER_SIZE + 2 * ELF_PROGRAM_ENTRY_SIZE + }; + + // ELF header + CODE ("\x7F" "ELF\x02\x01\x01") // ELF, 64-bit, little endian, v1 +#ifdef TARGET_OPENBSD + // OpenBSD either requires its ABI or a PT_NOTE with "OpenBSD" in it + CODE ("\x0C\x00" "\0\0\0\0\0\0\0") // OpenBSD ABI, v0, padding +#else + CODE ("\x00\x00" "\0\0\0\0\0\0\0") // Unix System V ABI, v0, padding +#endif + DW (2) DW (62) DD (1) // executable, x86-64, v1 + DQ (ELF_LOAD_CODE + ELF_META_SIZE) // entry point address + DQ (ELF_HEADER_SIZE) DQ (0) // program, section header offset + DD (0) // no processor-specific flags + DW (ELF_HEADER_SIZE) // ELF header size + DW (ELF_PROGRAM_ENTRY_SIZE) DW (2) // program hdr tbl entry size, count + DW (ELF_SECTION_ENTRY_SIZE) DW (0) // section hdr tbl entry size, count + DW (0) // no section index for strings + + // Program header for code + // The entry point address seems to require alignment, so map start of file + DD (1) DD (5) // PT_LOAD, PF_R | PF_X + DQ (0) // offset within the file + DQ (ELF_LOAD_CODE) // address in virtual memory + DQ (ELF_LOAD_CODE) // address in physical memory + DQ (ELF_META_SIZE + code.len) // length within the file + DQ (ELF_META_SIZE + code.len) // length within memory + DQ (4096) // segment alignment + + // Program header for the tape + DD (1) DD (6) // PT_LOAD, PF_R | PF_W + DQ (0) // offset within the file + DQ (ELF_LOAD_DATA) // address in virtual memory + DQ (ELF_LOAD_DATA) // address in physical memory + DQ (0) // length within the file + DQ (1 << 20) // one megabyte of memory + DQ (4096) // segment alignment + + // The section header table is optional and we don't need it for anything + + FILE *output_file; +#ifdef __unix__ + int output_fd; + if ((output_fd = open (output_path, O_CREAT | O_WRONLY, 0777)) < 0) + exit_fatal ("open: %s: %s\n", output_path, strerror (errno)); + if (!(output_file = fdopen (output_fd, "w"))) + exit_fatal ("fdopen: %s\n", strerror (errno)); +#else + if (!(output_file = fopen (output_path, "w"))) + exit_fatal ("fopen: %s: %s\n", output_path, strerror (errno)); +#endif + + fwrite (buffer.str, buffer.len, 1, output_file); + fwrite (code.str, code.len, 1, output_file); + fclose (output_file); + return 0; +} -- cgit v1.2.3-70-g09d2