[Lldb-commits] Possible UnwindAssembly-x86 Problem & Fix

[Tong Shen]

Hi jmolenda, lldb-commits,

While hacking around x86 assembly profiler, I found a problem about
non-volatile register information.

At UnwindAssembly-x86.cpp line 630 (ViewVC link
<http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Plugins/UnwindAssembly/x86/UnwindAssembly-x86.cpp?view=markup#l630>),
stack_offset is calculated but not used.
I think it should be used in line 636:
        regloc.SetAtCFAPlusOffset (-row->GetCFAOffset() + stack_offset);
instead of what's there now:
        regloc.SetAtCFAPlusOffset (-row->GetCFAOffset());

Also, in line 417 of the same file, when calculating stack_offset, why is
rbp_offset set to abs(offset)?

For testing, I wrote an assembly (test.S in attachment) to test if lldb can
recover non-volatile registers.
You can put a breakpoint after where asm_frame() overrides %rbx, then do "f
1" & "register read" to see if %rbx is correctly restored.
In my test, unmodified lldb gives wrong %rbx.
Attached patch solved this problem, and make lldb recover those registers
correctly.

Am I missing anything here? Is the original behavior intentional? Please
correct me if I'm wrong :-)

Thank you.

-- 
Best Regards, Tong Shen
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