Let arm_section_length store the number of bytes.

[ed]

Summary

Exception section data that we extract for DWARF gets stored as the
offset and the number of bytes. For ARM exception info, we seem to
deviate from this by storing the number of entries. Attempt to make this
more consistent.

By storing the number of bytes, we can get rid of the EHTEntry structure
declared in AddressSpace.hpp. In UnwindCursor.hpp we already have
another structure declared for the same purpose.

[keith.walker.arm]

This change looks OK to me.

The only side-effect that I can see is that the size of the __exidx_start and __exidx_end symbols in the object file will change in size from 8 to 1, but I don't think that should cause a problem.

[ed]

In D30681#694312, @keith.walker.arm wrote:

This change looks OK to me.

Perfect! Thanks for the quick review!

The only side-effect that I can see is that the size of the __exidx_start and __exidx_end symbols in the object file will change in size from 8 to 1, but I don't think that should cause a problem.

Yeah, exactly. They also are also extern declarations, so they should have no meaningful size at the object level.

src/AddressSpace.hpp

 #endif
 
 #include "libunwind.h"
 #include "config.h"
 #include "dwarf2.h"
 #include "Registers.hpp"
 
 #if _LIBUNWIND_ARM_EHABI
-struct EHTEntry {
-  uint32_t functionOffset;
-  uint32_t unwindOpcodes;
-};
 #if 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.
-extern EHTEntry __exidx_start;
-extern EHTEntry __exidx_end;
+extern char __exidx_start;
+extern char __exidx_end;
 #else
 #include <link.h>
 #endif // !defined(_LIBUNWIND_IS_BAREMETAL)
 #endif // _LIBUNWIND_ARM_EHABI
 
 #if defined(__CloudABI__) || defined(__FreeBSD__) || defined(__Fuchsia__) ||  \
     defined(__linux__) || defined(__NetBSD__)
 #if _LIBUNWIND_SUPPORT_DWARF_UNWIND && _LIBUNWIND_SUPPORT_DWARF_INDEX
#else // _LIBUNWIND_ARM_EHABI
           if (phdr->p_type == PT_LOAD) {
             uintptr_t begin = pinfo->dlpi_addr + 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 = pinfo->dlpi_addr + phdr->p_vaddr;
             cbdata->sects->arm_section = exidx_start;
-            cbdata->sects->arm_section_length = phdr->p_memsz /
-                                                sizeof(EHTEntry);
+            cbdata->sects->arm_section_length = phdr->p_memsz;
             found_hdr = true;
           }
         }
         return found_obj && found_hdr;
  #endif
       },
       &cb_data);
   return static_cast<bool>(found);

src/UnwindCursor.hpp

struct EHABISectionIterator {
   typedef typename A::pint_t& reference;
   typedef size_t size_type;
   typedef size_t difference_type;
 
   static _Self begin(A& addressSpace, const UnwindInfoSections& sects) {
     return _Self(addressSpace, sects, 0);
   }
   static _Self end(A& addressSpace, const UnwindInfoSections& sects) {
-    return _Self(addressSpace, sects, sects.arm_section_length);
+    return _Self(addressSpace, sects,
+                 sects.arm_section_length / sizeof(EHABIIndexEntry));
   }
 
   EHABISectionIterator(A& addressSpace, const UnwindInfoSections& sects, size_t i)
       : _i(i), _addressSpace(&addressSpace), _sects(&sects) {}
 
   _Self& operator++() { ++_i; return *this; }
   _Self& operator+=(size_t a) { _i += a; return *this; }
   _Self& operator--() { assert(_i > 0); --_i; return *this; }