[Lldb-commits] [PATCH] D34613: Add debug_frame section support

Pavel Labath via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Mon Jun 26 09:36:31 PDT 2017

labath added a comment.

In https://reviews.llvm.org/D34613#790745, @clayborg wrote:

> Glad this is happening. Does this mean we won't see the "bad eh frame" warnings anymore on linux? See inlined comments.

Unfortunately, I doubt it. This does nothing about eh_frame parsing, it just adds debug_frame support. So, you may start seeing more of those, as we will be parsing more stuff. :)

That said, I haven't seen that warning happen, at least not on x86. If you have a simple repro case, I could take a look.

Comment at: include/lldb/Symbol/DWARFCallFrameInfo.h:38
   DWARFCallFrameInfo(ObjectFile &objfile, lldb::SectionSP &section,
                      lldb::RegisterKind reg_kind, bool is_eh_frame);
clayborg wrote:
> Remove "reg_kind" and "is_eh_frame" and replace with DWARFCallFrameInfo::Type. See inlined comment below by the CFIVersion enum.
I think the enum could be used more prominently internally (I haven't checked that more closely yet). However, I think that using it here is wrong. The reason is that the decision which debug_frame version we are parsing does not happen at this level. This is a per-CIE property -- the same debug_frame section can contain CIE's with different version numbers (e.g. if they were compiled with different compilers or flags -- in fact, that's how I built my test module). At this level, all we need to know is whether we are parsing an eh_frame or debug_frame section, which is a still boolean value.

Theoretically, we could have a separate two-valued (eh, dwarf) enum here, and then, internally, when speaking about a specific CIE, use the 4-valued enum you proposed.

The register kind argument could probably be removed though.

Comment at: source/Symbol/FuncUnwinders.cpp:219-221
+  // Only supported on x86 architectures where we get debug_frame from the
+  // compiler that describes the prologue instructions perfectly, and sometimes
+  // the epilogue instructions too.
clayborg wrote:
> What compiler suddenly started including complete unwind info in .debug_frame? They are all supposed, but none ever have. MacOSX x86 and x86_64 has never done this right. I think this if statement is too inclusive. Can you narrow it down? I would love to see an example of this in action. I have never seen the x86 PIC bump code be properly described in any compiler. Are we trying to use this for unwinding frame zero? I would hope not unless we really and carefully know the exact compiler that produced the info. It would be preferable marked with an augmentation code that says "yes, I am really complete everywhere".
This is just copied from the equivalent eh_frame function, line 147 (which seems to have been added in r224689). I think what's that trying to say is that eh_frame/debug_frame augmentation is only supported on x86.


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