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[libunwind] Combine dl_iterate_phdr codepaths for DWARF and EHABI 

dl_iterate_phdr is used to search for unwind info provided by either
PT_GNU_EH_FRAME or PT_ARM_EXIDX. Most of the code between the two is
the same, so combine them, and factor out what's different into
checkForUnwindInfoSegment.

Details:
 - The FrameHeaderCache can now be enabled for ARM EHABI.
 - findUnwindSectionsByPhdr now finds the last PT_ARM_EXIDX rather than
   the first. There should only be one segment.
 - The dso_base and text_segment_length fields of UnwindInfoSections
   are now needed for dl_iterate_phdr when using EHABI, to hold the
   low and high PC values for a cache entry.

Reviewed By: compnerd, danielkiss, #libunwind, saugustine

Differential Revision: https://reviews.llvm.org/D87880
This commit is contained in:
Ryan Prichard 2020-09-23 14:25:13 -07:00
parent 38de1c33a8
commit b16d6653c0
2 changed files with 47 additions and 68 deletions
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114
libunwind/src/AddressSpace.hpp
View File

@ -114,13 +114,13 @@ namespace libunwind {
/// Used by findUnwindSections() to return info about needed sections.
struct UnwindInfoSections {
#if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) || defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) || \
defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
// No dso_base for SEH or ARM EHABI.
#if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) || \
defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND) || \
defined(_LIBUNWIND_USE_DL_ITERATE_PHDR)
// No dso_base for SEH.
uintptr_t dso_base;
#endif
#if defined(_LIBUNWIND_USE_DL_ITERATE_PHDR) && \
defined(_LIBUNWIND_SUPPORT_DWARF_INDEX)
#if defined(_LIBUNWIND_USE_DL_ITERATE_PHDR)
uintptr_t text_segment_length;
#endif
#if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
@ -394,11 +394,6 @@ struct _LIBUNWIND_HIDDEN dl_iterate_cb_data {
uintptr_t targetAddr;
};
#if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
#if !defined(_LIBUNWIND_SUPPORT_DWARF_INDEX)
#error "_LIBUNWIND_SUPPORT_DWARF_UNWIND requires _LIBUNWIND_SUPPORT_DWARF_INDEX on this platform."
#endif
#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
#include "FrameHeaderCache.hpp"
@ -421,6 +416,38 @@ static bool checkAddrInSegment(const Elf_Phdr *phdr, size_t image_base,
return false;
}
static bool checkForUnwindInfoSegment(const Elf_Phdr *phdr, size_t image_base,
dl_iterate_cb_data *cbdata) {
#if defined(_LIBUNWIND_SUPPORT_DWARF_INDEX)
if (phdr->p_type == PT_GNU_EH_FRAME) {
EHHeaderParser<LocalAddressSpace>::EHHeaderInfo hdrInfo;
uintptr_t eh_frame_hdr_start = image_base + phdr->p_vaddr;
cbdata->sects->dwarf_index_section = eh_frame_hdr_start;
cbdata->sects->dwarf_index_section_length = phdr->p_memsz;
if (EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
*cbdata->addressSpace, eh_frame_hdr_start, phdr->p_memsz,
hdrInfo)) {
// .eh_frame_hdr records the start of .eh_frame, but not its size.
// Rely on a zero terminator to find the end of the section.
cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
cbdata->sects->dwarf_section_length = UINTPTR_MAX;
return true;
}
}
return false;
#elif defined(_LIBUNWIND_ARM_EHABI)
if (phdr->p_type == PT_ARM_EXIDX) {
uintptr_t exidx_start = image_base + phdr->p_vaddr;
cbdata->sects->arm_section = exidx_start;
cbdata->sects->arm_section_length = phdr->p_memsz;
return true;
}
return false;
#else
#error Need one of _LIBUNWIND_SUPPORT_DWARF_INDEX or _LIBUNWIND_ARM_EHABI
#endif
}
static int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo,
size_t pinfo_size, void *data) {
auto cbdata = static_cast<dl_iterate_cb_data *>(data);
@ -435,35 +462,22 @@ static int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo,
#endif
Elf_Addr image_base = calculateImageBase(pinfo);
bool found_obj = false;
bool found_hdr = false;
bool found_text = false;
bool found_unwind = false;
// Third phdr is usually the executable phdr.
if (pinfo->dlpi_phnum > 2)
found_obj = checkAddrInSegment(&pinfo->dlpi_phdr[2], image_base, cbdata);
found_text = checkAddrInSegment(&pinfo->dlpi_phdr[2], image_base, cbdata);
// PT_GNU_EH_FRAME is usually near the end. Iterate backward. We already know
// that there is one or more phdrs.
// PT_GNU_EH_FRAME and PT_ARM_EXIDX are usually near the end. Iterate
// backward. We already know that there is one or more phdrs.
for (Elf_Half i = pinfo->dlpi_phnum; i > 0; i--) {
const Elf_Phdr *phdr = &pinfo->dlpi_phdr[i - 1];
if (!found_hdr && phdr->p_type == PT_GNU_EH_FRAME) {
EHHeaderParser<LocalAddressSpace>::EHHeaderInfo hdrInfo;
uintptr_t eh_frame_hdr_start = image_base + phdr->p_vaddr;
cbdata->sects->dwarf_index_section = eh_frame_hdr_start;
cbdata->sects->dwarf_index_section_length = phdr->p_memsz;
found_hdr = EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
*cbdata->addressSpace, eh_frame_hdr_start, phdr->p_memsz,
hdrInfo);
if (found_hdr) {
// .eh_frame_hdr records the start of .eh_frame, but not its size.
// Rely on a zero terminator to find the end of the section.
cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
cbdata->sects->dwarf_section_length = UINTPTR_MAX;
}
} else if (!found_obj) {
found_obj = checkAddrInSegment(phdr, image_base, cbdata);
}
if (found_obj && found_hdr) {
if (!found_unwind && checkForUnwindInfoSegment(phdr, image_base, cbdata))
found_unwind = true;
else if (!found_text && checkAddrInSegment(phdr, image_base, cbdata))
found_text = true;
if (found_text && found_unwind) {
#if defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
TheFrameHeaderCache.add(cbdata->sects);
#endif
@ -473,40 +487,6 @@ static int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo,
return 0;
}
#elif defined(_LIBUNWIND_ARM_EHABI)
static int findUnwindSectionsByPhdr(struct dl_phdr_info *pinfo, size_t,
void *data) {
auto *cbdata = static_cast<dl_iterate_cb_data *>(data);
bool found_obj = false;
bool found_hdr = false;
assert(cbdata);
assert(cbdata->sects);
if (cbdata->targetAddr < pinfo->dlpi_addr)
return 0;
Elf_Addr image_base = calculateImageBase(pinfo);
for (Elf_Half i = 0; i < pinfo->dlpi_phnum; i++) {
const Elf_Phdr *phdr = &pinfo->dlpi_phdr[i];
if (phdr->p_type == PT_LOAD) {
uintptr_t begin = image_base + phdr->p_vaddr;
uintptr_t end = begin + phdr->p_memsz;
if (cbdata->targetAddr >= begin && cbdata->targetAddr < end)
found_obj = true;
} else if (phdr->p_type == PT_ARM_EXIDX) {
uintptr_t exidx_start = image_base + phdr->p_vaddr;
cbdata->sects->arm_section = exidx_start;
cbdata->sects->arm_section_length = phdr->p_memsz;
found_hdr = true;
}
}
return found_obj && found_hdr;
}
#endif
#endif // defined(_LIBUNWIND_USE_DL_ITERATE_PHDR)

1
libunwind/test/frameheadercache_test.pass.cpp
View File

@ -5,7 +5,6 @@
// Only run this test under supported configurations.
#if defined(_LIBUNWIND_USE_DL_ITERATE_PHDR) && \
defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) && \
defined(_LIBUNWIND_USE_FRAME_HEADER_CACHE)
#include <link.h>