diff options
author | whitequark <whitequark@whitequark.org> | 2017-12-25 17:05:07 +0000 |
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committer | whitequark <whitequark@whitequark.org> | 2017-12-25 17:05:07 +0000 |
commit | 0b964a1ed14cfc93e1c9487f7cf14af8c7bc26ec (patch) | |
tree | d0e4f65b7fbbed07d56f160e31b9f8b5d996a2a8 | |
parent | 5d8a75e3d7badab5f069ced85b35057c9c620991 (diff) |
[libunwind] Add proper support for DWARF unwind on bare metal.
Right now, ARM EHABI unwind on bare metal expects to find the symbols
__exidx_start and __exidx_end defined, and uses those to locate
the EH tables. However, DWARF unwind on bare metal expects to find
dl_iterate_phdr, which, although possible to provide, is inconvenient
and mildly absurd.
This commit provides feature parity with ARM EHABI unwind by looking
for symbols __eh_frame_start, __eh_frame_end, __eh_frame_hdr_start
and __eh_frame_hdr_end, denoting the start and end of the sections
with corresponding names. As far as I know, there is no de jure or
de facto ABI providing any such names, so I chose the obvious ones.
The .eh_frame_hdr support is optional for maximum flexibility and
possible space savings (e.g. if libunwind is only used to provide
backtraces when a device crashes, providing the .eh_frame_hdr, which
is an index for rapid access to EH tables, would be a waste.)
The support for .eh_frame_hdr/DWARF index in the first place is
conditional on defined(_LIBUNWIND_SUPPORT_DWARF_INDEX), although
right now config.h will always define this macro.
The support for DWARF unwind on bare metal has been validated within
the ARTIQ environment[1].
[1]: https://m-labs.hk/artiq/
git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@321445 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | src/AddressSpace.hpp | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/src/AddressSpace.hpp b/src/AddressSpace.hpp index 2be16af..c9312a4 100644 --- a/src/AddressSpace.hpp +++ b/src/AddressSpace.hpp @@ -83,6 +83,38 @@ namespace libunwind { } #endif +#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL) + +// When statically linked on bare-metal, the symbols for the EH table are looked +// up without going through the dynamic loader. + +// The following linker script may be used to produce the necessary sections and symbols. +// Unless the --eh-frame-hdr linker option is provided, the section is not generated +// and does not take space in the output file. +// +// .eh_frame : +// { +// __eh_frame_start = .; +// KEEP(*(.eh_frame)) +// __eh_frame_end = .; +// } +// +// .eh_frame_hdr : +// { +// KEEP(*(.eh_frame_hdr)) +// } +// +// __eh_frame_hdr_start = SIZEOF(.eh_frame_hdr) > 0 ? ADDR(.eh_frame_hdr) : 0; +// __eh_frame_hdr_end = SIZEOF(.eh_frame_hdr) > 0 ? . : 0; + +extern char __eh_frame_start; +extern char __eh_frame_end; + +#if defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) +extern char __eh_frame_hdr_start; +extern char __eh_frame_hdr_end; +#endif + #elif defined(_LIBUNWIND_ARM_EHABI) && defined(_LIBUNWIND_IS_BAREMETAL) // When statically linked on bare-metal, the symbols for the EH table are looked @@ -348,6 +380,20 @@ inline bool LocalAddressSpace::findUnwindSections(pint_t targetAddr, info.compact_unwind_section_length = dyldInfo.compact_unwind_section_length; return true; } +#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL) + // Bare metal is statically linked, so no need to ask the dynamic loader + info.dwarf_section_length = (uintptr_t)(&__eh_frame_end - &__eh_frame_start); + info.dwarf_section = (uintptr_t)(&__eh_frame_start); + _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: section %X length %x", + info.dwarf_section, info.dwarf_section_length); +#if defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) + info.dwarf_index_section = (uintptr_t)(&__eh_frame_hdr_start); + info.dwarf_index_section_length = (uintptr_t)(&__eh_frame_hdr_end - &__eh_frame_hdr_start); + _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: index section %X length %x", + info.dwarf_index_section, info.dwarf_index_section_length); +#endif + if (info.dwarf_section_length) + return true; #elif defined(_LIBUNWIND_ARM_EHABI) && defined(_LIBUNWIND_IS_BAREMETAL) // Bare metal is statically linked, so no need to ask the dynamic loader info.arm_section = (uintptr_t)(&__exidx_start); |