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android: fallback to .dynsym when .gnu_debugdata fails

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This commit is contained in:
Kavish Devar
2026-04-23 18:43:54 +05:30
parent d82e4e2427
commit 113ee0a966
1 changed files with 105 additions and 46 deletions
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151
android/app/src/xposed/cpp/l2c_fcr_hook.cpp
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@@ -192,6 +192,65 @@ static uintptr_t getModuleBase(const char* name) {
return base;
}
static uint64_t findSymbolOffsetDynsym(
const std::vector<uint8_t>& elf,
const char* symbol_substring) {
LOGI("findSymbolOffsetDynsym called with %s", symbol_substring);
auto* eh = reinterpret_cast<const Elf64_Ehdr*>(elf.data());
auto* shdr = reinterpret_cast<const Elf64_Shdr*>(
elf.data() + eh->e_shoff);
const char* shstr =
reinterpret_cast<const char*>(
elf.data() + shdr[eh->e_shstrndx].sh_offset);
const Elf64_Shdr* dynsym = nullptr;
const Elf64_Shdr* dynstr = nullptr;
for (int i = 0; i < eh->e_shnum; ++i) {
const char* secname = shstr + shdr[i].sh_name;
if (!strcmp(secname, ".dynsym"))
dynsym = &shdr[i];
if (!strcmp(secname, ".dynstr"))
dynstr = &shdr[i];
}
if (!dynsym || !dynstr) {
LOGE("findSymbolOffsetDynsym: dynsym or dynstr not found");
return 0;
}
auto* symbols = reinterpret_cast<const Elf64_Sym*>(
elf.data() + dynsym->sh_offset);
const char* strings =
reinterpret_cast<const char*>(
elf.data() + dynstr->sh_offset);
size_t count = dynsym->sh_size / sizeof(Elf64_Sym);
LOGI("findSymbolOffsetDynsym: scanning %zu symbols", count);
for (size_t i = 0; i < count; ++i) {
const char* name = strings + symbols[i].st_name;
if (strstr(name, symbol_substring) &&
ELF64_ST_TYPE(symbols[i].st_info) == STT_FUNC) {
LOGI("findSymbolOffsetDynsym: matched %s @ 0x%lx",
name, (unsigned long)symbols[i].st_value);
return symbols[i].st_value;
}
}
LOGI("findSymbolOffsetDynsym: no match for %s", symbol_substring);
return 0;
}
static uint64_t findSymbolOffset(
const std::vector<uint8_t>& elf,
const char* symbol_substring) {
@@ -291,9 +350,10 @@ static bool hookLibrary(const char* libname) {
reinterpret_cast<const char*>(
file.data() + shdr[eh->e_shstrndx].sh_offset);
LOGI("hookLibrary: parsing ELF header and sections");
for (int i = 0; i < eh->e_shnum; ++i) {
uint64_t chk_offset = 0;
uint64_t sdp_offset = 0;
for (int i = 0; i < eh->e_shnum; ++i) {
if (!strcmp(shstr + shdr[i].sh_name, ".gnu_debugdata")) {
LOGI("hookLibrary: found .gnu_debugdata section");
@@ -303,60 +363,59 @@ static bool hookLibrary(const char* libname) {
std::vector<uint8_t> decompressed;
if (!decompressXZ(
if (decompressXZ(
compressed.data(),
compressed.size(),
decompressed)) {
LOGE("hookLibrary: decompressXZ failed");
return false;
}
LOGI("hookLibrary: decompressed debug data, size: %zu", decompressed.size());
uintptr_t base = getModuleBase(libname);
if (!base) {
LOGE("hookLibrary: getModuleBase failed");
return false;
}
LOGI("hookLibrary: module base: 0x%lx", base);
chk_offset = findSymbolOffset(decompressed,
"l2c_fcr_chk_chan_modes");
uint64_t chk_offset =
findSymbolOffset(decompressed,
"l2c_fcr_chk_chan_modes");
uint64_t sdp_offset =
findSymbolOffset(decompressed,
"BTA_DmSetLocalDiRecord");
LOGI("hookLibrary: chk_offset: 0x%lx, sdp_offset: 0x%lx", chk_offset, sdp_offset);
if (chk_offset) {
void* target =
reinterpret_cast<void*>(base + chk_offset);
hook_func(target,
(void*)fake_l2c_fcr_chk_chan_modes,
(void**)&original_l2c_fcr_chk_chan_modes);
LOGI("hookLibrary: hooked l2c_fcr_chk_chan_modes");
sdp_offset = findSymbolOffset(decompressed,
"BTA_DmSetLocalDiRecord");
} else {
LOGE("debugdata decompress failed");
}
if (sdp_offset) {
void* target =
reinterpret_cast<void*>(base + sdp_offset);
hook_func(target,
(void*)fake_BTA_DmSetLocalDiRecord,
(void**)&original_BTA_DmSetLocalDiRecord);
LOGI("hookLibrary: hooked BTA_DmSetLocalDiRecord");
}
return true;
break;
}
}
LOGI("hookLibrary: failed for %s", libname);
return false;
if (!chk_offset) {
LOGI("fallback dynsym chk");
chk_offset = findSymbolOffsetDynsym(file,
"l2c_fcr_chk_chan_modes");
}
if (!sdp_offset) {
LOGI("fallback dynsym sdp");
sdp_offset = findSymbolOffsetDynsym(file,
"BTA_DmSetLocalDiRecord");
}
uintptr_t base = getModuleBase(libname);
if (!base) {
LOGE("hookLibrary: getModuleBase failed");
return false;
}
if (chk_offset) {
void* target = reinterpret_cast<void*>(base + chk_offset);
hook_func(target,
(void*)fake_l2c_fcr_chk_chan_modes,
(void**)&original_l2c_fcr_chk_chan_modes);
LOGI("hooked chk");
}
if (sdp_offset) {
void* target = reinterpret_cast<void*>(base + sdp_offset);
hook_func(target,
(void*)fake_BTA_DmSetLocalDiRecord,
(void**)&original_BTA_DmSetLocalDiRecord);
LOGI("hooked sdp");
}
return chk_offset || sdp_offset;
}
static void on_library_loaded(const char* name, void*) {