[libunwind] [libunwind] Consistently pass start+length to decodeEHHdr() (PR #68813)

[Alexander Richardson via cfe-commits]

https://github.com/arichardson updated https://github.com/llvm/llvm-project/pull/68813

>From ff360ee7f304424dd0d12d00b8c0ba6801241410 Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson at google.com>
Date: Wed, 11 Oct 2023 08:34:55 -0700
Subject: [PATCH] [libunwind] Fix wrong end argument passed to decodeEHHdr()

All but one callsite were actually passing start+length arguments.
This should not have any functional change since the end argument is
almost always ignored.
I noticed this while debugging some incorrect error messages being
printed while running the testsuite baremetal (using binaries that did
not have a valid eh_frame_hdr section): the tests print
`libunwind: unsupported .eh_frame_hdr version: 20 at 8000d308` because
libunwind is reading nonsense data for .eh_frame_hdr.
---
 libunwind/src/AddressSpace.hpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/libunwind/src/AddressSpace.hpp b/libunwind/src/AddressSpace.hpp
index 1abbc822546878d..5551c7d4bef1c56 100644
--- a/libunwind/src/AddressSpace.hpp
+++ b/libunwind/src/AddressSpace.hpp
@@ -414,8 +414,8 @@ static bool checkForUnwindInfoSegment(const Elf_Phdr *phdr, size_t image_base,
     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)) {
+            *cbdata->addressSpace, eh_frame_hdr_start,
+            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;
@@ -638,7 +638,8 @@ inline bool LocalAddressSpace::findUnwindSections(pint_t targetAddr,
     info.dwarf_index_section_length = SIZE_MAX;
     EHHeaderParser<LocalAddressSpace>::EHHeaderInfo hdrInfo;
     if (!EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
-            *this, info.dwarf_index_section, info.dwarf_index_section_length,
+            *this, info.dwarf_index_section,
+            info.dwarf_index_section + info.dwarf_index_section_length,
             hdrInfo)) {
       return false;
     }