NekoCWD/libcamera
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libcamera: base: backtrace: Fallback to libunwind for symbolic names

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libunwind has an API to provide symbolic names for functions. It's less
optimal than using backtrace_symbols() or libdw, as it doesn't allow
deferring the symbolic names lookup, but it can be usefull as a fallback
if no other option is available.

A sample backtrace when falling back to libunwind looks like

libcamera::VimcCameraData::init()+0xbd
libcamera::PipelineHandlerVimc::match(libcamera::DeviceEnumerator*)+0x3e0
libcamera::CameraManager::Private::createPipelineHandlers()+0x1a7
libcamera::CameraManager::Private::init()+0x98
libcamera::CameraManager::Private::run()+0x9f
libcamera::Thread::startThread()+0xee
decltype(*(std::__1::forward<libcamera::Thread*>(fp0)).*fp()) std::__1::__invoke<void (libcamera::Thread::*)(), libcamera::Thread*, void>(void (libcamera::Thread::*&&)(), libcamera::Thread*&&)+0x77
void std::__1::__thread_execute<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (libcamera::Thread::*)(), libcamera::Thread*, 2ul>(std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (libcamera::Thread::*)(), libcamera::Thread*>&, std::__1::__tuple_indices<2ul>)+0x3e
void* std::__1::__thread_proxy<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, void (libcamera::Thread::*)(), libcamera::Thread*> >(void*)+0x62
start_thread+0xde
???

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
Laurent Pinchart 2021-09-24 05:05:51 +03:00
parent a7c7f58d59
commit 90a1720926
2 changed files with 37 additions and 1 deletions
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1
include/libcamera/base/backtrace.h
View file

@ -30,6 +30,7 @@ private:
bool unwindTrace();
std::vector<void *> backtrace_;
std::vector<std::string> backtraceText_;
};
} /* namespace libcamera */

37
src/libcamera/base/backtrace.cpp
View file

@ -202,6 +202,12 @@ bool Backtrace::unwindTrace()
return false;
do {
#if HAVE_BACKTRACE || HAVE_DW
/*
* If backtrace() or libdw is available, they will be used in
* toString() to provide symbol information for the stack
* frames using the IP register value.
*/
unw_word_t ip;
ret = unw_get_reg(&cursor, UNW_REG_IP, &ip);
if (ret) {
@ -210,6 +216,29 @@ bool Backtrace::unwindTrace()
}
backtrace_.push_back(reinterpret_cast<void *>(ip));
#else
/*
* Otherwise, use libunwind to get the symbol information. As
* the libunwind API uses cursors, we can't store the IP values
* and delay symbol lookup to toString().
*/
char symbol[256];
unw_word_t offset = 0;
ret = unw_get_proc_name(&cursor, symbol, sizeof(symbol), &offset);
if (ret) {
backtraceText_.emplace_back("???\n");
continue;
}
std::ostringstream entry;
char *name = abi::__cxa_demangle(symbol, nullptr, nullptr, nullptr);
entry << (name ? name : symbol);
free(name);
entry << "+0x" << std::hex << offset << "\n";
backtraceText_.emplace_back(entry.str());
#endif
} while (unw_step(&cursor) > 0);
return true;
@ -245,9 +274,15 @@ std::string Backtrace::toString(unsigned int skipLevels) const
*/
skipLevels += 2;
if (backtrace_.size() <= skipLevels)
if (backtrace_.size() <= skipLevels &&
backtraceText_.size() <= skipLevels)
return std::string();
if (!backtraceText_.empty()) {
Span<const std::string> trace{ backtraceText_ };
return utils::join(trace.subspan(skipLevels), "");
}
#if HAVE_DW
DwflParser dwfl;