w6a: DATAW directive for writable .data section
First step toward top-level mutable `let`. Adds a sibling directive to DATA whose bytes land in a separate writable .data PROGBITS section (SHF_ALLOC|SHF_WRITE, STT_OBJECT) instead of .text. The section is emitted only when DATAW was used, so inputs without it produce a byte-identical .o — tests 991 (selfhost .o diff) and 995 (self-rebuild) keep passing unchanged. w6l still treats data-resident syms as undefined; that's the next step.
This commit is contained in:
284
test/wcc/510_dataw.c
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284
test/wcc/510_dataw.c
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/*
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* 510_dataw — DATAW directive smoke. Assemble a tiny .s that uses
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* DATAW and verify the resulting .o has a writable .data section
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* containing the right bytes, with a symbol that points to it.
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*
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* Also confirms the no-DATAW path stays byte-identical to the
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* pre-DATAW format (6 sections, no .data); the selfhost .o diff in
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* 991 depends on that invariant.
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*/
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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 <unistd.h>
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#define SHT_PROGBITS 1
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#define SHT_SYMTAB 2
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#define SHF_WRITE 0x1
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#define SHF_ALLOC 0x2
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#define SHF_EXECINSTR 0x4
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#pragma pack(push, 1)
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typedef struct {
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uint8_t e_ident[16];
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uint16_t e_type, e_machine;
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uint32_t e_version;
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uint64_t e_entry, e_phoff, e_shoff;
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uint32_t e_flags;
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uint16_t e_ehsize, e_phentsize, e_phnum, e_shentsize, e_shnum, e_shstrndx;
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} Ehdr;
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typedef struct {
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uint32_t sh_name, sh_type;
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uint64_t sh_flags, sh_addr, sh_offset, sh_size;
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uint32_t sh_link, sh_info;
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uint64_t sh_addralign, sh_entsize;
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} Shdr;
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typedef struct {
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uint32_t st_name;
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uint8_t st_info, st_other;
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uint16_t st_shndx;
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uint64_t st_value, st_size;
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} Sym64;
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#pragma pack(pop)
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static int
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write_file(const char *path, const char *body)
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{
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FILE *f = fopen(path, "wb");
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if (!f) return -1;
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fputs(body, f);
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fclose(f);
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return 0;
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}
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static int
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slurp(const char *path, uint8_t **out, size_t *outn)
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{
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FILE *f = fopen(path, "rb");
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if (!f) return -1;
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fseek(f, 0, SEEK_END);
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long n = ftell(f);
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fseek(f, 0, SEEK_SET);
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uint8_t *b = malloc((size_t)n);
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if (fread(b, 1, (size_t)n, f) != (size_t)n) {
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free(b);
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fclose(f);
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return -1;
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}
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fclose(f);
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*out = b;
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*outn = (size_t)n;
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return 0;
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}
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/* Find the section with the given name. Returns index, or -1. */
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static int
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find_section(const uint8_t *buf, const char *name)
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{
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const Ehdr *eh = (const Ehdr *)buf;
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const Shdr *sh = (const Shdr *)(buf + eh->e_shoff);
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const char *shstr = (const char *)(buf + sh[eh->e_shstrndx].sh_offset);
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for (uint16_t i = 0; i < eh->e_shnum; i++) {
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if (strcmp(shstr + sh[i].sh_name, name) == 0)
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return (int)i;
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}
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return -1;
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}
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/* Find a symbol by name in the .symtab. Returns pointer, or NULL. */
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static const Sym64 *
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find_symbol(const uint8_t *buf, const char *name)
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{
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const Ehdr *eh = (const Ehdr *)buf;
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const Shdr *sh = (const Shdr *)(buf + eh->e_shoff);
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int idx_symtab = -1;
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for (uint16_t i = 0; i < eh->e_shnum; i++)
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if (sh[i].sh_type == SHT_SYMTAB) { idx_symtab = i; break; }
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if (idx_symtab < 0) return NULL;
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int idx_strtab = (int)sh[idx_symtab].sh_link;
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const Sym64 *syms = (const Sym64 *)(buf + sh[idx_symtab].sh_offset);
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uint64_t nsyms = sh[idx_symtab].sh_size / sizeof(Sym64);
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const char *str = (const char *)(buf + sh[idx_strtab].sh_offset);
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for (uint64_t i = 1; i < nsyms; i++) {
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if (strcmp(str + syms[i].st_name, name) == 0)
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return &syms[i];
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}
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return NULL;
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}
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static int
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test_dataw_emits_writable_section(const char *bin)
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{
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char src[64], obj[64];
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snprintf(src, sizeof src, "/tmp/wwt_dataw_%d.s", getpid());
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snprintf(obj, sizeof obj, "/tmp/wwt_dataw_%d.o", getpid());
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/* Hand-crafted .s: one writable data symbol holding 8 bytes (the
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* little-endian encoding of the i64 42) plus a trivial TEXT so
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* the assembler has something in .text to anchor. */
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const char *body =
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"TEXT _start(SB),$0\n"
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"\tMOVQ\t$0, AX\n"
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"\tRET\n"
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"DATAW counter(SB),\"\\x2a\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n";
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if (write_file(src, body) < 0) {
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fprintf(stderr, "dataw: cannot write %s\n", src);
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return -1;
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}
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char cmd[512];
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snprintf(cmd, sizeof cmd, "%s/w6a -o %s %s", bin, obj, src);
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if (system(cmd) != 0) {
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fprintf(stderr, "dataw: w6a failed\n");
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unlink(src);
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return -1;
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}
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uint8_t *buf = NULL;
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size_t n = 0;
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if (slurp(obj, &buf, &n) < 0) {
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fprintf(stderr, "dataw: cannot read .o\n");
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unlink(src); unlink(obj);
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return -1;
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}
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const Ehdr *eh = (const Ehdr *)buf;
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int rc = 0;
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/* Expect 7 sections: NULL, .text, .rela.text, .data, .symtab, .strtab, .shstrtab. */
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if (eh->e_shnum != 7) {
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fprintf(stderr, "dataw: e_shnum=%u, want 7\n", eh->e_shnum);
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rc = -1;
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}
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int idx_data = find_section(buf, ".data");
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if (idx_data < 0) {
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fprintf(stderr, "dataw: .data section not found\n");
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rc = -1;
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goto out;
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}
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const Shdr *sh = (const Shdr *)(buf + eh->e_shoff);
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const Shdr *sd = &sh[idx_data];
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if (sd->sh_type != SHT_PROGBITS) {
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fprintf(stderr, "dataw: .data sh_type=%u, want PROGBITS\n", sd->sh_type);
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rc = -1;
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}
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if ((sd->sh_flags & (SHF_ALLOC | SHF_WRITE)) != (SHF_ALLOC | SHF_WRITE)) {
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fprintf(stderr, "dataw: .data flags=0x%lx, want ALLOC|WRITE\n",
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(unsigned long)sd->sh_flags);
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rc = -1;
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}
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if ((sd->sh_flags & SHF_EXECINSTR) != 0) {
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fprintf(stderr, "dataw: .data is executable, want non-X\n");
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rc = -1;
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}
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if (sd->sh_size != 8) {
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fprintf(stderr, "dataw: .data size=%lu, want 8\n",
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(unsigned long)sd->sh_size);
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rc = -1;
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}
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/* Verify the bytes themselves match the LE i64 42 we wrote. */
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const uint8_t *db = buf + sd->sh_offset;
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uint8_t want[8] = { 0x2a, 0, 0, 0, 0, 0, 0, 0 };
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if (memcmp(db, want, 8) != 0) {
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fprintf(stderr, "dataw: .data contents mismatch\n");
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rc = -1;
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}
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const Sym64 *s = find_symbol(buf, "counter");
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if (s == NULL) {
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fprintf(stderr, "dataw: symbol 'counter' not in .symtab\n");
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rc = -1;
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goto out;
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}
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if ((int)s->st_shndx != idx_data) {
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fprintf(stderr, "dataw: 'counter'.st_shndx=%u, want %d (.data)\n",
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s->st_shndx, idx_data);
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rc = -1;
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}
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if (s->st_value != 0) {
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fprintf(stderr, "dataw: 'counter'.st_value=%lu, want 0\n",
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(unsigned long)s->st_value);
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rc = -1;
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}
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out:
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free(buf);
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unlink(src);
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unlink(obj);
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return rc;
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}
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static int
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test_no_dataw_keeps_legacy_layout(const char *bin)
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{
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char src[64], obj[64];
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snprintf(src, sizeof src, "/tmp/wwt_nodataw_%d.s", getpid());
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snprintf(obj, sizeof obj, "/tmp/wwt_nodataw_%d.o", getpid());
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/* A .s without any DATAW must still produce the legacy 6-section
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* layout. Test 991 (selfhost .o byte-diff) relies on this. */
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const char *body =
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"TEXT _start(SB),$0\n"
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"\tMOVQ\t$0, AX\n"
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"\tRET\n";
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if (write_file(src, body) < 0) {
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fprintf(stderr, "nodataw: cannot write %s\n", src);
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return -1;
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}
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char cmd[512];
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snprintf(cmd, sizeof cmd, "%s/w6a -o %s %s", bin, obj, src);
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if (system(cmd) != 0) {
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fprintf(stderr, "nodataw: w6a failed\n");
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unlink(src);
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return -1;
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}
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uint8_t *buf = NULL;
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size_t n = 0;
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if (slurp(obj, &buf, &n) < 0) {
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fprintf(stderr, "nodataw: cannot read .o\n");
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unlink(src); unlink(obj);
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return -1;
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}
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const Ehdr *eh = (const Ehdr *)buf;
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int rc = 0;
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if (eh->e_shnum != 6) {
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fprintf(stderr, "nodataw: e_shnum=%u, want 6 (legacy)\n",
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eh->e_shnum);
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rc = -1;
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}
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if (find_section(buf, ".data") >= 0) {
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fprintf(stderr, "nodataw: .data section present, want absent\n");
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rc = -1;
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}
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free(buf);
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unlink(src);
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unlink(obj);
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return rc;
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}
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int
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main(void)
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{
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const char *bin = getenv("BIN");
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if (!bin) bin = "out/bin";
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int fail = 0;
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if (test_dataw_emits_writable_section(bin) != 0) fail++;
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if (test_no_dataw_keeps_legacy_layout(bin) != 0) fail++;
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if (fail) {
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fprintf(stderr, "dataw: %d/2 subtests failed\n", fail);
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return 1;
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}
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printf("dataw: 2/2 ok\n");
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return 0;
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}
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