328 lines
8.8 KiB
C
328 lines
8.8 KiB
C
// This is an exercise in futility more than anything else
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdint.h>
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#include <stdbool.h>
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#include <assert.h>
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#include <errno.h>
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#if (defined __x86_64__ || defined __amd64__) && defined __unix__
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#include <sys/mman.h>
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#else
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#error Platform not supported
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#endif
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#define exit_fatal(...) \
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do { \
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fprintf (stderr, "fatal: " __VA_ARGS__); \
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exit (EXIT_FAILURE); \
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} while (0)
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// --- Safe memory management --------------------------------------------------
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static void *
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xcalloc (size_t m, size_t n)
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{
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void *p = calloc (m, n);
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if (!p)
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exit_fatal ("calloc: %s\n", strerror (errno));
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return p;
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}
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static void *
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xrealloc (void *o, size_t n)
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{
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void *p = realloc (o, n);
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if (!p && n)
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exit_fatal ("realloc: %s\n", strerror (errno));
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return p;
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}
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// --- Dynamically allocated strings -------------------------------------------
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struct str
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{
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char *str; ///< String data, null terminated
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size_t alloc; ///< How many bytes are allocated
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size_t len; ///< How long the string actually is
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};
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static void
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str_init (struct str *self)
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{
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self->len = 0;
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self->str = xcalloc (1, (self->alloc = 16));
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}
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static void
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str_ensure_space (struct str *self, size_t n)
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{
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// We allocate at least one more byte for the terminating null character
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size_t new_alloc = self->alloc;
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while (new_alloc <= self->len + n)
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new_alloc <<= 1;
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if (new_alloc != self->alloc)
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self->str = xrealloc (self->str, (self->alloc = new_alloc));
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}
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static void
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str_append_data (struct str *self, const void *data, size_t n)
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{
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str_ensure_space (self, n);
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memcpy (self->str + self->len, data, n);
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self->str[self->len += n] = '\0';
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}
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static void
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str_append_c (struct str *self, char c)
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{
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str_append_data (self, &c, 1);
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}
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// --- Application -------------------------------------------------------------
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struct str data; ///< Data tape
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volatile size_t dataptr; ///< Current location on the tape
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FILE *input; ///< User input
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enum command { RIGHT, LEFT, INC, DEC, SET, IN, OUT, BEGIN, END };
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bool grouped[] = { 1, 1, 1, 1, 1, 0, 0, 0, 0 };
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struct instruction { enum command cmd; size_t arg; };
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// - - Callbacks - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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// Some things I just really don't want to write in assembly even though it
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// is effectively a big performance hit, eliminating the advantage of JIT
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static void
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right (size_t arg)
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{
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assert (SIZE_MAX - dataptr > arg);
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dataptr += arg;
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while (dataptr >= data.len)
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str_append_c (&data, 0);
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}
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static void
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left (size_t arg)
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{
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assert (dataptr >= arg);
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dataptr -= arg;
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}
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static int
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cin (void)
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{
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int c = fgetc (input);
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assert (c != EOF);
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return c;
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}
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// - - Main - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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int
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main (int argc, char *argv[])
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{
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(void) argc;
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(void) argv;
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struct str program;
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str_init (&program);
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int c;
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while ((c = fgetc (stdin)) != EOF)
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str_append_c (&program, c);
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if (ferror (stdin))
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exit_fatal ("can't read program\n");
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if (!(input = fopen ("/dev/tty", "rb")))
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exit_fatal ("can't open terminal for reading\n");
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// - - Decode and group - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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struct instruction *parsed = xcalloc (sizeof *parsed, program.len);
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size_t parsed_len = 0;
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for (size_t i = 0; i < program.len; i++)
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{
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enum command cmd;
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switch (program.str[i])
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{
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case '>': cmd = RIGHT; break;
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case '<': cmd = LEFT; break;
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case '+': cmd = INC; break;
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case '-': cmd = DEC; break;
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case '.': cmd = OUT; break;
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case ',': cmd = IN; break;
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case '[': cmd = BEGIN; break;
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case ']': cmd = END; break;
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default: continue;
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}
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if (!parsed_len || !grouped[cmd] || parsed[parsed_len - 1].cmd != cmd)
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parsed_len++;
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parsed[parsed_len - 1].cmd = cmd;
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parsed[parsed_len - 1].arg++;
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}
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// - - Simple optimization pass - - - - - - - - - - - - - - - - - - - - - - - -
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size_t in = 0, out = 0;
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for (; in < parsed_len; in++, out++)
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{
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if (in + 2 < parsed_len
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&& parsed[in ].cmd == BEGIN
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&& parsed[in + 1].cmd == DEC && parsed[in + 1].arg == 1
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&& parsed[in + 2].cmd == END)
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{
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parsed[out].cmd = SET;
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parsed[out].arg = 0;
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in += 2;
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}
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else if (out && parsed[out - 1].cmd == SET && parsed[in].cmd == INC)
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parsed[--out].arg += parsed[in].arg;
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else if (out != in)
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parsed[out] = parsed[in];
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}
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parsed_len = out;
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// - - Loop pairing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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size_t nesting = 0;
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size_t *stack = xcalloc (sizeof *stack, parsed_len);
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for (size_t i = 0; i < parsed_len; i++)
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{
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switch (parsed[i].cmd)
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{
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case BEGIN:
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stack[nesting++] = i;
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break;
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case END:
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assert (nesting > 0);
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--nesting;
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parsed[stack[nesting]].arg = i + 1;
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parsed[i].arg = stack[nesting] + 1;
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default:
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break;
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}
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}
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free (stack);
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assert (nesting == 0);
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// - - JIT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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// Functions preserve the registers rbx, rsp, rbp, r12, r13, r14, and r15;
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// while rax, rdi, rsi, rdx, rcx, r8, r9, r10, r11 are scratch registers.
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str_init (&program);
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size_t *offsets = xcalloc (sizeof *offsets, parsed_len + 1);
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#define CODE(x) { char t[] = x; str_append_data (&program, t, sizeof t - 1); }
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#define WORD(x) { size_t t = (size_t)(x); str_append_data (&program, &t, 8); }
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CODE ("\x49\xBD") WORD (&dataptr) // mov r13, qword "&dataptr"
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CODE ("\x49\xBF") WORD (&data.str) // mov r15, qword "&data.str"
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CODE ("\x4D\x8B\x37") // mov r14, qword [r15]
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CODE ("\x30\xDB") // xor bl, bl
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for (size_t i = 0; i < parsed_len; i++)
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{
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offsets[i] = program.len;
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size_t arg = parsed[i].arg;
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switch (parsed[i].cmd)
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{
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case RIGHT:
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CODE ("\x41\x88\x1E") // mov [r14], bl
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CODE ("\x48\xBF") WORD (arg) // mov rdi, "arg"
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CODE ("\x48\xB8") WORD (right) // mov rax, "right"
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CODE ("\xFF\xD0") // call rax
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// The data could get reallocated, so reload the address
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CODE ("\x4D\x8B\x37") // mov r14, qword [r15]
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CODE ("\x4D\x03\x75\x00") // add r14, [r13]
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CODE ("\x41\x8A\x1E") // mov bl, [r14]
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break;
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case LEFT:
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CODE ("\x41\x88\x1E") // mov [r14], bl
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CODE ("\x48\xBF") WORD (arg) // mov rdi, "arg"
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CODE ("\x49\x29\xFE") // sub r14, rdi -- optimistic
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CODE ("\x48\xB8") WORD (left) // mov rax, "left"
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CODE ("\xFF\xD0") // call rax
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CODE ("\x41\x8A\x1E") // mov bl, [r14]
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break;
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case INC:
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CODE ("\x80\xC3") // add bl, "arg"
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str_append_c (&program, arg);
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break;
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case DEC:
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CODE ("\x80\xEB") // sub bl, "arg"
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str_append_c (&program, arg);
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break;
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case SET:
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CODE ("\xB3") // mov bl, "arg"
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str_append_c (&program, arg);
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break;
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case OUT:
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CODE ("\x48\x0F\xB6\xFB") // movzx rdi, bl
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CODE ("\x48\xBE") WORD (stdout) // mov rsi, "stdout"
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CODE ("\x48\xB8") WORD (fputc) // mov rax, "fputc"
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CODE ("\xFF\xD0") // call rax
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break;
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case IN:
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CODE ("\x48\xB8") WORD (cin) // mov rax, "cin"
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CODE ("\xFF\xD0") // call rax
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CODE ("\x88\xC3") // mov bl, al
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break;
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case BEGIN:
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CODE ("\x84\xDB") // test bl, bl
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CODE ("\x0F\x84\x00\x00\x00\x00") // jz "offsets[i]"
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break;
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case END:
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CODE ("\x84\xDB") // test bl, bl
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CODE ("\x0F\x85\x00\x00\x00\x00") // jnz "offsets[i]"
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break;
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}
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}
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// When there is a loop at the end we need to be able to jump past it
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offsets[parsed_len] = program.len;
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str_append_c (&program, '\xC3'); // ret
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// Now that we know where each instruction is, fill in relative jumps
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for (size_t i = 0; i < parsed_len; i++)
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{
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if (parsed[i].cmd != BEGIN && parsed[i].cmd != END)
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continue;
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size_t fixup = offsets[i] + 4;
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*(int32_t *)(program.str + fixup) =
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((intptr_t)(offsets[parsed[i].arg]) - (intptr_t)(fixup + 4));
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}
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free (offsets);
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// - - Runtime - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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// Some systems may have W^X
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void *executable = mmap (NULL, program.len, PROT_READ | PROT_WRITE,
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MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (!executable)
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exit_fatal ("mmap: %s\n", strerror (errno));
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memcpy (executable, program.str, program.len);
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if (mprotect (executable, program.len, PROT_READ | PROT_EXEC))
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exit_fatal ("mprotect: %s\n", strerror (errno));
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str_init (&data);
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str_append_c (&data, 0);
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((void (*) (void)) executable)();
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return 0;
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}
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