[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 §ion,
lldb::RegisterKind reg_kind, bool is_eh_frame);
> 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.
> 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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