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FIX(overlay): Implement library search list for dlsym(), add "libc.so…
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….6" to it

glibc 2.34 moved all functionality of various libraries into the main one.
As a result, dlsym() is now exported by libc instead of libdl.

This commit also makes the related code more robust.
We now iterate through a common library name/path list, regardless of the OS.
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@davidebeatrici
davidebeatrici committed Nov 6, 2022
1 parent bf4ad2b commit 84535d8
Showing 1 changed file with 112 additions and 100 deletions.
212 changes: 112 additions & 100 deletions overlay_gl/init_unix.c
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Original file line number Diff line number Diff line change
Expand Up @@ -162,125 +162,137 @@ __attribute__((visibility("default"))) void *dlsym(void *handle, const char *nam
}

static int find_odlsym() {
#if defined(__linux__)
void *dl = dlopen("libdl.so.2", RTLD_LAZY);
if (!dl) {
ods("Failed to open libdl.so.2!");
return -1;
}
// clang-format off
const char *libs[] = {
"libc.so.6",
"libdl.so.2",
"/libexec/ld-elf.so.1"
};
// clang-format on

for (uint8_t libIdx = 0; libIdx < sizeof(libs) / sizeof(libs[0]); ++libIdx) {
const char *lib = libs[libIdx];
ods("Searching for dlsym() in \"%s\"...", lib);
#ifdef RTLD_SELF
struct link_map *lm = NULL;
if (dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &lm) == -1) {
ods("Unable to acquire link_map: %s", dlerror());
return -1;
}

struct link_map *lm = dl;
#elif defined(__FreeBSD__)
struct link_map *lm = NULL;
if (dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &lm) == -1) {
ods("Unable to acquire link_map: %s", dlerror());
return -1;
}
while (lm) {
if (strcmp(lm->l_name, lib) == 0) {
break;
}

while (lm) {
if (strcmp(lm->l_name, "/libexec/ld-elf.so.1") == 0) {
break;
lm = lm->l_next;
}

lm = lm->l_next;
}
if (!lm) {
ods("Failed to find \"%s\"!", lib);
continue;
}
#else
void *dl = dlopen(lib, RTLD_LAZY);
if (!dl) {
ods("dlopen() failed: %s", dlerror());
continue;
}

if (!lm) {
ods("Failed to find ld-elf.so.1!");
return -1;
}
const struct link_map *lm = dl;
#endif
bool hashTableGNU = false;
uintptr_t hashTable = 0;
const char *strTable = NULL;
Elf_Sym *symTable = NULL;
bool hashTableGNU = false;
uintptr_t hashTable = 0;
const char *strTable = NULL;
Elf_Sym *symTable = NULL;
#if defined(__GLIBC__)
const uintptr_t base = 0;
const uintptr_t base = 0;
#else
const uintptr_t base = (uintptr_t) lm->l_addr;
const uintptr_t base = (uintptr_t) lm->l_addr;
#endif
for (const Elf_Dyn *dyn = lm->l_ld; dyn; ++dyn) {
switch (dyn->d_tag) {
case DT_GNU_HASH:
if (!hashTable) {
hashTable = base + dyn->d_un.d_ptr;
hashTableGNU = true;
}
break;
case DT_HASH:
if (!hashTable) {
hashTable = base + dyn->d_un.d_ptr;
}
break;
case DT_STRTAB:
strTable = (const char *) (base + dyn->d_un.d_ptr);
break;
case DT_SYMTAB:
symTable = (Elf_Sym *) (base + dyn->d_un.d_ptr);
for (const Elf_Dyn *dyn = lm->l_ld; dyn; ++dyn) {
switch (dyn->d_tag) {
case DT_GNU_HASH:
if (!hashTable) {
hashTable = base + dyn->d_un.d_ptr;
hashTableGNU = true;
}
break;
case DT_HASH:
if (!hashTable) {
hashTable = base + dyn->d_un.d_ptr;
}
break;
case DT_STRTAB:
strTable = (const char *) (base + dyn->d_un.d_ptr);
break;
case DT_SYMTAB:
symTable = (Elf_Sym *) (base + dyn->d_un.d_ptr);
break;
}

if (hashTable && strTable && symTable) {
break;
}
}

if (hashTable && strTable && symTable) {
break;
}
}
ods("hashTable: 0x%" PRIxPTR ", strTable: %p, symTable: %p", hashTable, strTable, symTable);

ods("hashTable: 0x%" PRIxPTR ", strTable: %p, symTable: %p", hashTable, strTable, symTable);
if (!hashTable || !strTable || !symTable) {
continue;
}

if (!hashTable || !strTable || !symTable) {
return -1;
}
if (!hashTableGNU) {
ods("Using DT_HASH");
// Hash table pseudo-struct:
// uint32_t nBucket;
// uint32_t nChain;
// uint32_t bucket[nBucket];
// uint32_t chain[nChain];
const uint32_t nChain = ((uint32_t *) hashTable)[1];

for (uint32_t i = 0; i < nChain; ++i) {
if (ELF_ST_TYPE(symTable[i].st_info) != STT_FUNC) {
continue;
}

if (!hashTableGNU) {
ods("Using DT_HASH");
// Hash table pseudo-struct:
// uint32_t nBucket;
// uint32_t nChain;
// uint32_t bucket[nBucket];
// uint32_t chain[nChain];
const uint32_t nChain = ((uint32_t *) hashTable)[1];

for (uint32_t i = 0; i < nChain; ++i) {
if (ELF_ST_TYPE(symTable[i].st_info) != STT_FUNC) {
continue;
if (strcmp(strTable + symTable[i].st_name, "dlsym") == 0) {
odlsym = (void *) lm->l_addr + symTable[i].st_value;
break;
}
}
} else {
ods("Using DT_GNU_HASH");
// Hash table pseudo-struct:
// uint32_t nBucket;
// uint32_t symOffset;
// uint32_t nBloom;
// uint32_t bloomShift;
// uintptr_t blooms[nBloom];
// uint32_t buckets[nBucket];
// uint32_t chain[];
uint32_t *hashStruct = (uint32_t *) hashTable;

const uint32_t nBucket = hashStruct[0];
const uint32_t symOffset = hashStruct[1];
const uint32_t nBloom = hashStruct[2];
const uintptr_t *bloom = (uintptr_t *) &hashStruct[4];
const uint32_t *buckets = (uint32_t *) &bloom[nBloom];
const uint32_t *chain = &buckets[nBucket];

for (uint32_t i = 0; i < nBucket; ++i) {
uint32_t symIndex = buckets[i];
if (symIndex < symOffset) {
continue;
}

if (strcmp(strTable + symTable[i].st_name, "dlsym") == 0) {
odlsym = (void *) lm->l_addr + symTable[i].st_value;
break;
do {
if (strcmp(strTable + symTable[symIndex].st_name, "dlsym") == 0) {
odlsym = (void *) lm->l_addr + symTable[symIndex].st_value;
}
} while (!odlsym && !(chain[symIndex++ - symOffset] & 1));
}
}
} else {
ods("Using DT_GNU_HASH");
// Hash table pseudo-struct:
// uint32_t nBucket;
// uint32_t symOffset;
// uint32_t nBloom;
// uint32_t bloomShift;
// uintptr_t blooms[nBloom];
// uint32_t buckets[nBucket];
// uint32_t chain[];
uint32_t *hashStruct = (uint32_t *) hashTable;

const uint32_t nBucket = hashStruct[0];
const uint32_t symOffset = hashStruct[1];
const uint32_t nBloom = hashStruct[2];
const uintptr_t *bloom = (uintptr_t *) &hashStruct[4];
const uint32_t *buckets = (uint32_t *) &bloom[nBloom];
const uint32_t *chain = &buckets[nBucket];

for (uint32_t i = 0; i < nBucket; ++i) {
uint32_t symIndex = buckets[i];
if (symIndex < symOffset) {
continue;
}

do {
if (strcmp(strTable + symTable[symIndex].st_name, "dlsym") == 0) {
odlsym = (void *) lm->l_addr + symTable[symIndex].st_value;
}
} while (!odlsym && !(chain[symIndex++ - symOffset] & 1));
}
}

if (!odlsym) {
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