mstorsjo created this revision.
Herald added a subscriber: aprantl.
If the linker chose to store the full section name instead of truncating it,
this field doesn't contain a truncated name, but an offset into the string
table of the binary. The string table isn't loaded/mapped into memory during
runtime though, so it's not possible to read the full section name, unless we
try to locate the DLL/EXE on disk that the HMODULE corresponds to and load that
manually.
This also has the practical consequence that with the current LLD, we must not
enable debug info (i.e. must link with -s with the mingw frontend). If debug
info is enabled, the full ".eh_frame" name is written into the string table and
the the section name itself is just an offset, e.g. "/4".
Alternatives to fixing this consequence are:
- Making LLD always output a truncated ".eh_fram" (maybe only when -lldmingw is
specified?), even if debug info is enabled. (GNU ld doesn't do this, so this
approach in libunwind won't work with binaries built with that.)
- Switch to statically registering the .eh_frame sections on startup, instead
of dynamically enumerating them when needed. This is what libgcc does. This
doesn't match what libunwind does on other platforms though. This only works as
long as libunwind is linked dynamically so that all involved DLLs register
their sections to the same instance of libunwind. (I haven't succeeded in
building a shared libcxx/libcxxabi/libunwind yet for mingw though.)
https://reviews.llvm.org/D39918
Files:
src/AddressSpace.hpp
Index: src/AddressSpace.hpp
===================================================================
--- src/AddressSpace.hpp
+++ src/AddressSpace.hpp
@@ -382,8 +382,6 @@
found_obj = true;
} else if (!strncmp((const char *)pish->Name, ".eh_frame",
IMAGE_SIZEOF_SHORT_NAME)) {
- // FIXME: This section name actually is truncated, ideally we
- // should locate and check the full long name instead.
info.dwarf_section = begin;
info.dwarf_section_length = pish->Misc.VirtualSize;
found_hdr = true;
Index: src/AddressSpace.hpp
===================================================================
--- src/AddressSpace.hpp
+++ src/AddressSpace.hpp
@@ -382,8 +382,6 @@
found_obj = true;
} else if (!strncmp((const char *)pish->Name, ".eh_frame",
IMAGE_SIZEOF_SHORT_NAME)) {
- // FIXME: This section name actually is truncated, ideally we
- // should locate and check the full long name instead.
info.dwarf_section = begin;
info.dwarf_section_length = pish->Misc.VirtualSize;
found_hdr = true;
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