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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libunwind

Author: Alexander Richardson (arichardson)

<details>
<summary>Changes</summary>

It previously took a start+end pint_t, but 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.

---
Full diff: https://github.com/llvm/llvm-project/pull/68813.diff


1 Files Affected:

- (modified) libunwind/src/EHHeaderParser.hpp (+4-3) 


``````````diff
diff --git a/libunwind/src/EHHeaderParser.hpp b/libunwind/src/EHHeaderParser.hpp
index ed4317c89055c9e..2162178e10bb2fb 100644
--- a/libunwind/src/EHHeaderParser.hpp
+++ b/libunwind/src/EHHeaderParser.hpp
@@ -35,7 +35,7 @@ template <typename A> class EHHeaderParser {
     uint8_t table_enc;
   };
 
-  static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
+  static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, size_t ehHdrSize,
                           EHHeaderInfo &ehHdrInfo);
   static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
                       uint32_t sectionLength,
@@ -53,8 +53,9 @@ template <typename A> class EHHeaderParser {
 
 template <typename A>
 bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
-                                    pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
+                                    size_t ehHdrSize, EHHeaderInfo &ehHdrInfo) {
   pint_t p = ehHdrStart;
+  pint_t ehHdrEnd = ehHdrStart + ehHdrSize;
   uint8_t version = addressSpace.get8(p++);
   if (version != 1) {
     _LIBUNWIND_LOG("unsupported .eh_frame_hdr version: %" PRIu8 " at %" PRIx64,
@@ -106,7 +107,7 @@ bool EHHeaderParser<A>::findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
   pint_t ehHdrEnd = ehHdrStart + sectionLength;
 
   EHHeaderParser<A>::EHHeaderInfo hdrInfo;
-  if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,
+  if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, sectionLength,
                                       hdrInfo))
     return false;
 

``````````

</details>


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