What is this not happening on any other architecture? Is the "$" special for
MIPS and not for other architectures? We really don't want to remove the '$' as
we want the symbol to be unique. The '$' symbol is fine for all x86/x86_64/arm
and arm64 variants...
Greg
> On Oct 19, 2015, at 11:30 PM, Bhushan Attarde via lldb-dev
> <lldb-dev@lists.llvm.org> wrote:
>
> Hi,
>
> I am facing issue (llvm assertion) in evaluating expressions for MIPS on
> Linux.
>
> (lldb) p fooptr(a,b)
> lldb: /home/battarde/git/llvm/lib/MC/ELFObjectWriter.cpp:791: void
> {anonymous}::ELFObjectWriter::computeSymbolTable(llvm::MCAssembler&, const
> llvm::MCAsmLayout&, const SectionIndexMapTy&, const RevGroupMapTy&,
> {anonymous}::ELFObjectWriter::SectionOffsetsTy&): Assertion `Local ||
> !Symbol.isTemporary()' failed.
>
> I debugged it and found that, LLDB inserts calls to dynamic checker function
> for pointer validation at appropriate locations in expression’s IR.
>
> The issue is that this checker function’s name (hard-coded in LLDB in
> lldb\source\Expression\IRDynamicChecks.cpp) starts with “$” i.e
> “$__lldb_valid_pointer_check”.
> While creating a MCSymbol (MCContext::createSymbol() in
> llvm/lib/MC/MCContext.cpp) for this function llvm detects the name starts
> with “$” and marks that symbol as ‘temporary’ symbol (PrivateGlobalPrefix is
> '$' for MIPS)
> Further while computing a symbol table in
> ELFObjectWriter::computeSymbolTable() the assertion triggers because this
> symbol is 'temporary'.
>
> I tried couple of things that solves this issue for MIPS.
>
> 1. Remove '$' from the function name.
> 2. Remove "C Language linkage" from the dynamic pointer validation function
> i.e the below piece of code in lldb\source\Expression\IRDynamicChecks.cpp
> ---------------------------------------------------------------------
> static const char g_valid_pointer_check_text[] =
> "extern \"C\" void\n"
> "$__lldb_valid_pointer_check (unsigned char *$__lldb_arg_ptr)\n"
> "{\n"
> " unsigned char $__lldb_local_val = *$__lldb_arg_ptr;\n"
> "}";
> ----------------------------------------------------------------------
>
> becomes
>
> --------------------------------------------------------------------
> static const char g_valid_pointer_check_text[] =
> "void\n"
> "$__lldb_valid_pointer_check (unsigned char *$__lldb_arg_ptr)\n"
> "{\n"
> " unsigned char $__lldb_local_val = *$__lldb_arg_ptr;\n"
> "}";
> --------------------------------------------------------------------
>
> Removing C Language linkage will enable mangling and will mangle
> "$__lldb_valid_pointer_check" to something like
> "_Z27$__lldb_valid_pointer_checkPh".
> So the mangled name won't start with '$' and the symbol will not be marked as
> Temporary and hence assertion won't be triggered.
>
> Please let me know if there is any better solution to this issue.
>
> Regards,
> Bhushan
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