Hojun-Cho
2480f4c272
Scan the consolidated .data buffer (post-relocation) for trailing zero bytes; set the R+W PT_LOAD's p_filesz to exclude them while p_memsz covers the full region. The loader zero-fills the gap, so behaviour is unchanged. Saves up to a page per binary on programs whose globals are zero-init. Mirrored in selfhost/cmd/w6l/out.ww so test 992's byte-identity diff still holds. Dynamic-link path is untouched — it still errors on any mutable global; that's the next feature.
338 lines
8.9 KiB
C
338 lines
8.9 KiB
C
/*
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* 620_data_link — end-to-end w6l support for writable globals.
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* Assemble a small .s using DATAW, link it with w6l, run the binary,
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* and verify both that the read returns the global's value and that
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* a store updates it. Also confirms the binary has two PT_LOADs with
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* the right R+X / R+W flags.
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*
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* Inputs without DATAW must still produce the single-PT_LOAD layout
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* — 992 (selfhost w6l .o diff) 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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#include <sys/wait.h>
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#define PT_LOAD 1
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#define PF_X 1
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#define PF_W 2
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#define PF_R 4
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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 p_type, p_flags;
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uint64_t p_offset, p_vaddr, p_paddr;
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uint64_t p_filesz, p_memsz, p_align;
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} Phdr;
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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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static int
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build(const char *bin, const char *body, const char *exe)
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{
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char src[64], obj[64], cmd[1024];
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snprintf(src, sizeof src, "/tmp/wwt_dl_%d.s", getpid());
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snprintf(obj, sizeof obj, "/tmp/wwt_dl_%d.o", getpid());
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if (write_file(src, body) < 0) return -1;
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snprintf(cmd, sizeof cmd, "%s/w6a -o %s %s", bin, obj, src);
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if (system(cmd) != 0) { unlink(src); return -1; }
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snprintf(cmd, sizeof cmd, "%s/w6l -o %s %s", bin, exe, obj);
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int rc = system(cmd);
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unlink(src); unlink(obj);
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return rc;
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}
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static int
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run_exit(const char *exe)
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{
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int rc = system(exe);
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if (rc == -1) return -1;
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if (WIFEXITED(rc)) return WEXITSTATUS(rc);
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return -1;
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}
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/* Test 1: read a writable global. _start exits with the value stored
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* in `counter` (0x2a == 42). */
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static int
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test_read(const char *bin)
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{
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char exe[64];
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snprintf(exe, sizeof exe, "/tmp/wwt_dl_%d.x1", getpid());
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const char *body =
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"TEXT _start,$0\n"
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"\tMOVQ\tcounter(SB), DI\n"
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"\tMOVQ\t$60, AX\n"
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"\tSYSCALL\n"
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"DATAW counter(SB),\"\\x2a\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n";
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if (build(bin, body, exe) != 0) {
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fprintf(stderr, "test_read: build failed\n");
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return -1;
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}
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int rc = run_exit(exe);
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unlink(exe);
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if (rc != 42) {
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fprintf(stderr, "test_read: exit=%d, want 42\n", rc);
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return -1;
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}
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return 0;
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}
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/* Test 2: store to a writable global, read it back, exit with the new
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* value. Verifies the R+W mapping really is writable. */
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static int
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test_write(const char *bin)
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{
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char exe[64];
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snprintf(exe, sizeof exe, "/tmp/wwt_dl_%d.x2", getpid());
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const char *body =
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"TEXT _start,$0\n"
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"\tMOVQ\t$99, AX\n"
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"\tMOVQ\tAX, counter(SB)\n"
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"\tMOVQ\tcounter(SB), DI\n"
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"\tMOVQ\t$60, AX\n"
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"\tSYSCALL\n"
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"DATAW counter(SB),\"\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n";
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if (build(bin, body, exe) != 0) {
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fprintf(stderr, "test_write: build failed\n");
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return -1;
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}
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int rc = run_exit(exe);
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unlink(exe);
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if (rc != 99) {
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fprintf(stderr, "test_write: exit=%d, want 99\n", rc);
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return -1;
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}
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return 0;
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}
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/* Test 3: structurally inspect the linked ELF — two PT_LOADs, the
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* first R+X and the second R+W. Catches regressions where the layout
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* is right but the flags or count are off. */
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static int
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test_two_loads(const char *bin)
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{
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char exe[64];
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snprintf(exe, sizeof exe, "/tmp/wwt_dl_%d.x3", getpid());
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const char *body =
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"TEXT _start,$0\n"
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"\tMOVQ\tcounter(SB), AX\n"
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"\tMOVQ\t$60, AX\n"
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"\tMOVQ\t$0, DI\n"
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"\tSYSCALL\n"
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"DATAW counter(SB),\"\\x01\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n";
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if (build(bin, body, exe) != 0) {
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fprintf(stderr, "test_two_loads: build failed\n");
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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(exe, &buf, &n) < 0) {
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fprintf(stderr, "test_two_loads: cannot read exe\n");
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unlink(exe);
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return -1;
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}
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unlink(exe);
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const Ehdr *eh = (const Ehdr *)buf;
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int rc = 0;
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if (eh->e_phnum != 2) {
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fprintf(stderr, "test_two_loads: e_phnum=%u, want 2\n", eh->e_phnum);
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rc = -1;
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goto out;
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}
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const Phdr *ph = (const Phdr *)(buf + eh->e_phoff);
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int saw_rx = 0, saw_rw = 0;
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for (int i = 0; i < 2; i++) {
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if (ph[i].p_type != PT_LOAD) {
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fprintf(stderr, "test_two_loads: ph[%d] not PT_LOAD\n", i);
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rc = -1;
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continue;
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}
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if (ph[i].p_flags == (PF_R | PF_X)) saw_rx = 1;
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else if (ph[i].p_flags == (PF_R | PF_W)) saw_rw = 1;
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else {
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fprintf(stderr, "test_two_loads: ph[%d] flags=0x%x\n",
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i, ph[i].p_flags);
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rc = -1;
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}
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}
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if (!saw_rx) { fprintf(stderr, "test_two_loads: missing R+X\n"); rc = -1; }
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if (!saw_rw) { fprintf(stderr, "test_two_loads: missing R+W\n"); rc = -1; }
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out:
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free(buf);
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return rc;
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}
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/* Test 4: an input without DATAW still produces a single PT_LOAD.
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* 992 (selfhost w6l .o diff) depends on this byte-level invariant. */
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static int
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test_no_data_single_load(const char *bin)
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{
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char exe[64];
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snprintf(exe, sizeof exe, "/tmp/wwt_dl_%d.x4", getpid());
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const char *body =
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"TEXT _start,$0\n"
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"\tMOVQ\t$60, AX\n"
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"\tMOVQ\t$0, DI\n"
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"\tSYSCALL\n";
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if (build(bin, body, exe) != 0) {
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fprintf(stderr, "test_no_data_single_load: build failed\n");
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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(exe, &buf, &n) < 0) {
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fprintf(stderr, "test_no_data_single_load: cannot read exe\n");
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unlink(exe);
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return -1;
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}
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unlink(exe);
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int rc = 0;
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const Ehdr *eh = (const Ehdr *)buf;
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if (eh->e_phnum != 1) {
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fprintf(stderr, "test_no_data_single_load: e_phnum=%u, want 1\n",
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eh->e_phnum);
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rc = -1;
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}
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free(buf);
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return rc;
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}
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/* Test 5: BSS optimisation — trailing zero bytes in .data are dropped
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* from the file (p_filesz < p_memsz) and the loader zero-fills the gap.
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* Asserts that a trailing zero-init slot doesn't bloat the binary. */
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static int
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test_bss_filesz(const char *bin)
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{
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char exe[64];
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snprintf(exe, sizeof exe, "/tmp/wwt_dl_%d.x5", getpid());
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/* Two DATAW slots: a 1-byte non-zero followed by a 31-byte zero
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* run. Memsz must cover all 32B; filesz should stop after the 1B
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* non-zero (so file_data == 1, memsz_data == 32). */
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const char *body =
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"TEXT _start,$0\n"
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"\tMOVQ\tnz(SB), DI\n"
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"\tMOVQ\t$60, AX\n"
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"\tSYSCALL\n"
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"DATAW nz(SB),\"\\x07\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n"
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"DATAW zlong(SB),\"\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00"
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"\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00"
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"\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n";
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if (build(bin, body, exe) != 0) {
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fprintf(stderr, "test_bss_filesz: build failed\n");
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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(exe, &buf, &n) < 0) {
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fprintf(stderr, "test_bss_filesz: cannot read exe\n");
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unlink(exe);
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return -1;
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}
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int rc = 0;
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const Ehdr *eh = (const Ehdr *)buf;
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const Phdr *ph = (const Phdr *)(buf + eh->e_phoff);
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int saw_rw = 0;
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for (int i = 0; i < eh->e_phnum; i++) {
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if (ph[i].p_type != PT_LOAD) continue;
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if (ph[i].p_flags != (PF_R | PF_W)) continue;
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saw_rw = 1;
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if (ph[i].p_filesz >= ph[i].p_memsz) {
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fprintf(stderr, "test_bss_filesz: filesz=%lu, "
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"memsz=%lu (want filesz<memsz)\n",
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(unsigned long)ph[i].p_filesz,
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(unsigned long)ph[i].p_memsz);
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rc = -1;
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}
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/* The scan trims every trailing zero — it doesn't know
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* symbol boundaries. nz is \x07 then 7 zero bytes, so
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* the file ends at byte 1 (the 0x07). Memsz still covers
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* all 32B and the loader zero-fills. */
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if (ph[i].p_filesz != 1) {
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fprintf(stderr, "test_bss_filesz: filesz=%lu, "
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"want 1\n", (unsigned long)ph[i].p_filesz);
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rc = -1;
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}
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if (ph[i].p_memsz != 32) {
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fprintf(stderr, "test_bss_filesz: memsz=%lu, "
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"want 32\n", (unsigned long)ph[i].p_memsz);
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rc = -1;
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}
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}
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if (!saw_rw) {
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fprintf(stderr, "test_bss_filesz: no R+W PT_LOAD found\n");
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rc = -1;
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}
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free(buf);
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if (rc != 0) { unlink(exe); return rc; }
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/* Behaviour check: the zero-init slot must still read as zero
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* at runtime — the loader has to zero-fill the BSS gap. */
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int er = run_exit(exe);
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unlink(exe);
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if (er != 7) {
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fprintf(stderr, "test_bss_filesz: exit=%d, want 7\n", er);
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return -1;
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}
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return 0;
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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_read(bin) != 0) fail++;
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if (test_write(bin) != 0) fail++;
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if (test_two_loads(bin) != 0) fail++;
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if (test_no_data_single_load(bin) != 0) fail++;
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if (test_bss_filesz(bin) != 0) fail++;
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if (fail) {
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fprintf(stderr, "data_link: %d/5 subtests failed\n", fail);
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return 1;
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}
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printf("data_link: 5/5 ok\n");
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return 0;
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}
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