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osx: fix the chained-fixups reader so Unity 6.3 games hook #117

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Merged
ManlyMarco merged 1 commit into from
Sep 24, 2026
Merged

osx: fix the chained-fixups reader so Unity 6.3 games hook #117

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31 changes: 29 additions & 2 deletions src/nix/plthook/plthook_osx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,7 @@ typedef struct {
struct segment_command_64 *segments[MAX_SEGMENTS];
struct linkedit_data_command *chained_fixups;
size_t got_addr;
size_t got_size;
} data_t;

static int plthook_open_real(plthook_t **plthook_out, uint32_t image_idx, const struct mach_header *mh, const char *image_name);
Expand Down Expand Up @@ -397,6 +398,7 @@ static int plthook_open_real(plthook_t **plthook_out, uint32_t image_idx, const
sec->reserved3);
if (strcmp(sec->segname, "__DATA_CONST") == 0 && strcmp(sec->sectname, "__got") == 0) {
data.got_addr = sec->addr + data.slide;
data.got_size = sec->size;
}
sec++;
}
Expand Down Expand Up @@ -613,9 +615,34 @@ static void set_bind_addr(data_t *data, unsigned int *idx, const char *sym_name,
(*idx)++;
}


/* Chained fixups bind every slot before the image runs, so a slot can be
identified by what it holds. The import list order is not the __got layout
order, so index arithmetic picks the wrong slot. */
static void **chained_slot_for(data_t *d, const char *name, uint32_t index)
{
size_t nslots = d->got_size / sizeof(void *);
const char *sym = (name[0] == '_') ? name + 1 : name;
size_t i;

for (i = 0; i < nslots; i++) {
void **slot = (void **)(d->got_addr + i * sizeof(void *));
Dl_info info;
if (dladdr(*slot, &info) && info.dli_sname != NULL
&& strcmp(info.dli_sname, sym) == 0) {
return slot;
}
}
/* Not bound to a named symbol; fall back to the old arithmetic. */
return (void **)(d->got_addr + index * sizeof(void *));
}

static int read_chained_fixups(data_t *d, const struct mach_header *mh, const char *image_name)
{
const uint8_t *ptr = (const uint8_t *)mh + d->chained_fixups->dataoff;
const struct segment_command_64 *linkedit = d->segments[d->linkedit_segment_idx];
/* dataoff is a file offset; linkedit is mapped at a different delta */
const uint8_t *ptr = (const uint8_t *)(linkedit->vmaddr - linkedit->fileoff
+ d->slide + d->chained_fixups->dataoff);
const uint8_t *end = ptr + d->chained_fixups->datasize;
const struct dyld_chained_fixups_header *header = (const struct dyld_chained_fixups_header *)ptr;
const struct dyld_chained_import *import = (const struct dyld_chained_import *)(ptr + header->imports_offset);
Expand Down Expand Up @@ -712,7 +739,7 @@ static int read_chained_fixups(data_t *d, const struct mach_header *mh, const ch
DEBUG_FIXUPS(" lib_ordinal %u, weak_import %u, name_offset %u (%s), addend %llu\n",
imp.lib_ordinal, imp.weak_import, imp.name_offset, name, imp.addend);
d->plthook->entries[i].name = name;
d->plthook->entries[i].addr = (void**)(d->got_addr + i * sizeof(void*));
d->plthook->entries[i].addr = chained_slot_for(d, name, i);
}

#ifdef PLTHOOK_DEBUG_FIXUPS
Expand Down
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