https://bugs.llvm.org/show_bug.cgi?id=45114
Bug ID: 45114
Summary: PDB debug info CV_ALLREG_VFRAME issue in 32 bit
output, probably alignment problem
Product: new-bugs
Version: 10.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
First of all I am sorry I could not conjure a simple testcase, but the problem
depends on compiler emitting CV_ALLREG_VFRAME local variable records into the
database and those are hard to reproduce with small code.
I have downloaded toolchain here
https://github.com/mstorsjo/llvm-mingw/releases
Our small opensource project maintains ide environment that has native .pdb
debugging support (using dbghelp.dll) so I have started experimenting with llvm
pdb output.
C:\upp\bin/clang\bin\i686-w64-mingw32-c++.exe -c -mthreads -g2 -static
-fexceptions -D_DEBUG -O0 -g -gcodeview -fno-limit-debug-info
-fno-omit-frame-pointer -x c++ "C:\u\PdbTests\main.cpp" -o
"C:/out/PdbTests/main.o"
Soon I have found that address of some local variables is 4 bytes off. Further
investigation revealed that the problem was for local variable symbols with
PSYMBOL_INFO.Register == CV_ALLREG_VFRAME.
After some more digging, I believe the issue is related to this:
The start of function looks like
004018D0 push ebp
004018D1 mov ebp,esp <----
004018D3 push esi
004018D4 and esp,byte -0x8 <----
004018D7 sub esp,0xc80
So there is an alignment of esp, but the value in epb is still unaligned.
However the values emmitted to .pdb in PSYMBOL_INFO.Address seem to be relative
to ALIGNED value, which sometimes leads to offset being invalid by 4. (All
further addresses in the code are esp based).
I have tried following workaround in our debugger:
.....
if(pSym->Flags & IMAGEHLP_SYMBOL_INFO_REGRELATIVE) {
if(pSym->Register == CV_ALLREG_VFRAME) {
if(c.pdb->win64)
v.address += c.pdb->GetCpuRegister(*c.context,
CV_AMD64_RBP);
else
{
adr_t ebp =
(adr_t)c.pdb->GetCpuRegister(*c.context, CV_REG_EBP);
if(c.pdb->clang)
ebp &= ~(adr_t)7; // Workaround for
supposed clang/win32 issue
v.address += ebp;
}
}
else
v.address += (adr_t)c.pdb->GetCpuRegister(*c.context,
pSym->Register);
}
.....
and that seems to completely fix the issue, but I think this still counts like
a bug... also posting this here for future reference for other unfortunate
debugger developers...
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