[libunwind] [libunwind] Add length info for dynamic .eh_frame registration (PR #77185)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libunwind

Author: None (SihangZhu)

<details>
<summary>Changes</summary>

Fix this issue [#<!-- -->76957](https://github.com/llvm/llvm-project/issues/76957)
Libgcc provides __register_frame  to register a dynamic .eh_frame section, while __unw_add_dynamic_eh_frame_section can be used to do the same in libunwind. However, the address after dynamic .eh_frame are padding with 0 value, it will be identified as 
legal CIE. And __unw_add_dynamic_eh_frame_section will continue to parse subsequent addresses until illegal memory or other sections are accessed.
This patch adds length formal parameter for dynamic registration.


---
Full diff: https://github.com/llvm/llvm-project/pull/77185.diff


2 Files Affected:

- (modified) libunwind/src/libunwind.cpp (+3-2) 
- (modified) libunwind/src/libunwind_ext.h (+1-1) 


``````````diff
diff --git a/libunwind/src/libunwind.cpp b/libunwind/src/libunwind.cpp
index cd610377b63de8..7d78d167b83434 100644
--- a/libunwind/src/libunwind.cpp
+++ b/libunwind/src/libunwind.cpp
@@ -318,13 +318,14 @@ void __unw_remove_dynamic_fde(unw_word_t fde) {
   DwarfFDECache<LocalAddressSpace>::removeAllIn((LocalAddressSpace::pint_t)fde);
 }
 
-void __unw_add_dynamic_eh_frame_section(unw_word_t eh_frame_start) {
+void __unw_add_dynamic_eh_frame_section(unw_word_t eh_frame_start, size_t length) {
   // The eh_frame section start serves as the mh_group
   unw_word_t mh_group = eh_frame_start;
   CFI_Parser<LocalAddressSpace>::CIE_Info cieInfo;
   CFI_Parser<LocalAddressSpace>::FDE_Info fdeInfo;
   auto p = (LocalAddressSpace::pint_t)eh_frame_start;
-  while (true) {
+  auto end = p + length;
+  while (p < end) {
     if (CFI_Parser<LocalAddressSpace>::decodeFDE(
             LocalAddressSpace::sThisAddressSpace, p, &fdeInfo, &cieInfo,
             true) == NULL) {
diff --git a/libunwind/src/libunwind_ext.h b/libunwind/src/libunwind_ext.h
index 28db43a4f6eef2..1bfb595c46130f 100644
--- a/libunwind/src/libunwind_ext.h
+++ b/libunwind/src/libunwind_ext.h
@@ -55,7 +55,7 @@ extern void __unw_iterate_dwarf_unwind_cache(void (*func)(
 extern void __unw_add_dynamic_fde(unw_word_t fde);
 extern void __unw_remove_dynamic_fde(unw_word_t fde);
 
-extern void __unw_add_dynamic_eh_frame_section(unw_word_t eh_frame_start);
+extern void __unw_add_dynamic_eh_frame_section(unw_word_t eh_frame_start, size_t length);
 extern void __unw_remove_dynamic_eh_frame_section(unw_word_t eh_frame_start);
 
 #ifdef __APPLE__

``````````

</details>


https://github.com/llvm/llvm-project/pull/77185