[PATCH] [libcxxabi] Make _Unwind_Backtrace() work on ARM.

[Jonathan Roelofs]

Added comments. See attached.

On 9/9/14 11:35 AM, Jonathan Roelofs wrote:
>
>
> On 9/9/14 3:22 AM, Renato Golin wrote:
>> On 8 September 2014 18:36, Jonathan Roelofs <jonathan at codesourcery.com> wrote:
>>> Anddd, here's the patch.
>>
>> Hi Jon,
>>
>> Would be good to not need to duplicate the personality declaration
>> inside the function. Maybe include the eh header? Not sure...
> That function isn't exposed in any of the headers, and this is sort of a
> layering violation (Unwinder looking for libcxxabi symbols). I'm not sure which
> header it would belong in if I were to add it. Suggestions?
>>
>> Also, would be good to add a big comment on why we do that check and
>> what needs to be done to support other personality routines (ex.
>> __aeabi_unwind_cpp_pr0).
> The compact ones are already supported... so good point! :)
>
> Cheers,
> Jon
>>
>> cheers,
>> --renato
>>
>

-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded
-------------- next part --------------
Index: src/Unwind/Unwind-EHABI.cpp
===================================================================
--- src/Unwind/Unwind-EHABI.cpp	(revision 217387)
+++ src/Unwind/Unwind-EHABI.cpp	(working copy)
@@ -218,11 +218,25 @@
 decode_eht_entry(const uint32_t* data, size_t* off, size_t* len) {
   if ((*data & 0x80000000) == 0) {
     // 6.2: Generic Model
-    *off = 1; // First byte is size data.
-    *len = (((data[1] >> 24) & 0xff) + 1) * 4;
+    // EHT entry is a prel31 pointing to the PR, followed by data understood only
+    // by the personality routine. Since EHABI doesn't guarantee the location or
+    // availability of the unwind opcodes in the generic model, we have to check
+    // for them on a case-by-case basis:
+    _Unwind_Reason_Code __gxx_personality_v0(int version, _Unwind_Action actions,
+                                             uint64_t exceptionClass,
+                                             _Unwind_Exception* unwind_exception,
+                                             _Unwind_Context* context);
+    void *PR = (void*)signExtendPrel31(*data);
+    if (PR == &__gxx_personality_v0) {
+      *off = 1; // First byte is size data.
+      *len = (((data[1] >> 24) & 0xff) + 1) * 4;
+    } else
+      return nullptr;
     data++; // Skip the first word, which is the prel31 offset.
   } else {
     // 6.3: ARM Compact Model
+    // EHT entries here correspond to the __aeabi_unwind_cpp_pr[012] PRs indeded
+    // by format:
     Descriptor::Format format =
         static_cast<Descriptor::Format>((*data & 0x0f000000) >> 24);
     switch (format) {
@@ -241,7 +255,7 @@
   }
 
   return data;
-}
+}sdfasdf
 
 _Unwind_Reason_Code _Unwind_VRS_Interpret(
     _Unwind_Context* context,