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Some comments regarding dlfcn logistics and comment cleanup

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Jeremy 2024-05-25 00:40:08 -05:00
parent eb5417baae
commit dad3bd1843
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2 changed files with 8 additions and 7 deletions
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12
src/binary/object.cpp
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@ -39,6 +39,9 @@ namespace detail {
}
}
#endif
// dladdr queries are needed to get pre-ASLR addresses and targets to run symbol resolution on
// _dl_find_object is preferred if at all possible as it is much faster (added in glibc 2.35)
// dladdr1 is preferred if possible because it allows for a more accurate object path to be resolved (glibc 2.3.3)
#ifdef CPPTRACE_HAS_DL_FIND_OBJECT // we don't even check for this on apple
object_frame get_frame_object_info(frame_ptr address) {
// Use _dl_find_object when we can, it's orders of magnitude faster
@ -53,9 +56,7 @@ namespace detail {
return frame;
}
#elif defined(HAS_DLADDR1)
// dladdr queries are needed to get pre-ASLR addresses and targets to run addr2line on
object_frame get_frame_object_info(frame_ptr address) {
// reference: https://github.com/bminor/glibc/blob/master/debug/backtracesyms.c
// https://github.com/bminor/glibc/blob/91695ee4598b39d181ab8df579b888a8863c4cab/elf/dl-addr.c#L26
Dl_info info;
link_map* link_map_info;
@ -79,9 +80,9 @@ namespace detail {
return frame;
}
#else
// TODO: Try to verify this is correct in the context of bad argv[0]
// macos doesn't have dladdr1 but it seems its dli_fname behaves more sensibly?
// dladdr queries are needed to get pre-ASLR addresses and targets to run addr2line on
// glibc dladdr may not return an accurate dli_fname as it uses argv[0] for addresses in the main executable
// https://github.com/bminor/glibc/blob/caed1f5c0b2e31b5f4e0f21fea4b2c9ecd3b5b30/elf/dl-addr.c#L33-L36
// macos doesn't have dladdr1 but its dli_fname behaves more sensibly, same with some other libc's like musl
object_frame get_frame_object_info(frame_ptr address) {
// reference: https://github.com/bminor/glibc/blob/master/debug/backtracesyms.c
Dl_info info;
@ -111,7 +112,6 @@ namespace detail {
if(it == cache.end()) {
char path[MAX_PATH];
if(GetModuleFileNameA(handle, path, sizeof(path))) {
///std::fprintf(stderr, "path: %s base: %p\n", path, handle);
cache.insert(it, {handle, path});
return path;
} else {

3
src/binary/safe_dl.cpp
View File

@ -23,7 +23,7 @@ namespace detail {
void get_safe_object_frame(frame_ptr address, safe_object_frame* out) {
out->raw_address = address;
dl_find_object result;
if(_dl_find_object(reinterpret_cast<void*>(address), &result) == 0) {
if(_dl_find_object(reinterpret_cast<void*>(address), &result) == 0) { // thread-safe, signal-safe
out->address_relative_to_object_start = address - to_frame_ptr(result.dlfo_link_map->l_addr);
if(result.dlfo_link_map->l_name != nullptr && result.dlfo_link_map->l_name[0] != 0) {
std::size_t path_length = std::strlen(result.dlfo_link_map->l_name);
@ -35,6 +35,7 @@ namespace detail {
} else {
// empty l_name, this means it's the currently running executable
memset(out->object_path, 0, CPPTRACE_PATH_MAX + 1);
// signal-safe
auto res = readlink("/proc/self/exe", out->object_path, CPPTRACE_PATH_MAX);
if(res == -1) {
// error handling?