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Temporarily disable libunwind's FrameHeaderCache, until there is a

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resolution for <https://bugs.llvm.org/show_bug.cgi?id=47181>.

The cache implementation depends on dl_iterate_phdr(3) ensuring that its
callbacks are not called simultaneously for multiple threads, but that
is only the case for the dl_iterate_phdr() implementation in rtld.

In a statically linked executable, libc's dl_iterate_phdr() is used,
which does no such locking. If multiple threads then call into the
unwinder at the same time, it is possible to trigger a segfault.

In particular, the statically linked lld which is built during the
cross-tools stage can segfault in this way, because it starts multiple
worker threads that can exit in parallel. Since our pthread_exit(3)
invokes the unwinder, it will therefore call into it in parallel too.
This commit is contained in:
Dimitry Andric 2020-08-15 22:58:07 +00:00
parent 1106035d5b
commit 9ff1cc58cd
1 changed files with 6 additions and 0 deletions
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6
contrib/llvm-project/libunwind/src/AddressSpace.hpp
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@ -452,10 +452,12 @@ struct _LIBUNWIND_HIDDEN dl_iterate_cb_data {
#error "_LIBUNWIND_SUPPORT_DWARF_UNWIND requires _LIBUNWIND_SUPPORT_DWARF_INDEX on this platform."
#endif
#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
#include "FrameHeaderCache.hpp"
// There should be just one of these per process.
static FrameHeaderCache ProcessFrameHeaderCache;
#endif // _LIBUNWIND_USE_FRAME_HEADER_CACHE
static bool checkAddrInSegment(const Elf_Phdr *phdr, size_t image_base,
dl_iterate_cb_data *cbdata) {
@ -476,8 +478,10 @@ int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo, size_t pinfo_size,
auto cbdata = static_cast<dl_iterate_cb_data *>(data);
if (pinfo->dlpi_phnum == 0 || cbdata->targetAddr < pinfo->dlpi_addr)
return 0;
#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
if (ProcessFrameHeaderCache.find(pinfo, pinfo_size, data))
return 1;
#endif // _LIBUNWIND_USE_FRAME_HEADER_CACHE
Elf_Addr image_base = calculateImageBase(pinfo);
bool found_obj = false;
@ -505,7 +509,9 @@ int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo, size_t pinfo_size,
found_obj = checkAddrInSegment(phdr, image_base, cbdata);
}
if (found_obj && found_hdr) {
#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
ProcessFrameHeaderCache.add(cbdata->sects);
#endif // _LIBUNWIND_USE_FRAME_HEADER_CACHE
return 1;
}
}