Hi Greg, I tried using "_$" and "lldb$" as our private prefix, both of these solves the issue and works fine for MIPS.
-Regards, Bhushan -----Original Message----- From: Greg Clayton [mailto:gclay...@apple.com] Sent: 23 October 2015 22:29 To: Bhushan Attarde Cc: lldb-dev@lists.llvm.org Subject: Re: [lldb-dev] llvm assertion while evaluating expressions for MIPS on Linux What happens if we go with "_$" as our private prefix? Or maybe "lldb$"? Would this avoid the issue and fix things for MIPS? I would rather us have a consistent private naming scheme across all architectures. Let me know if you can try that out and let us know if this works. Greg > On Oct 23, 2015, at 5:03 AM, Bhushan Attarde <bhushan.atta...@imgtec.com> > wrote: > > Hi Greg, > > Thanks for your reply. > > There are different temporary symbols for different architectures and file > formats. > As far as I could see, llvm::MCAsmInfo class has a member > "PrivateGlobalPrefix" which specifies this temporary symbol. > The default value for PrivateGlobalPrefix is 'L' (for ELF it is ".L"). > The subclasses of llvm::MCAsmInfo sets PrivateGlobalPrefix to whatever value > they want to use for temporary symbol. > MIPS sets this to "$". (and X86/ARM uses ".L") > > Since the function name "$__lldb_valid_pointer_check" starts with "$" it > matches with PrivateGlobalPrefix for MIPS and hence it is marked as temporary. > Its fine for all x86/x86_64/arm and arm64 variants because they all use > symbol other than "$" (i.e ".L") as their PrivateGlobalPrefix. > > As you mentioned we cannot remove "$" from function name because it > may conflict with symbols from system libraries or user binaries, so do you > think removing C Language linkage from function "$__lldb_valid_pointer_check" > can be a solution? or do you have a better solution to this issue? > > Regards, > Bhushan > > > -----Original Message----- > From: Greg Clayton [mailto:gclay...@apple.com] > Sent: 20 October 2015 23:56 > To: Greg Clayton > Cc: Bhushan Attarde; lldb-dev@lists.llvm.org > Subject: Re: [lldb-dev] llvm assertion while evaluating expressions > for MIPS on Linux > > My guess is that there is a different temporary symbol for differing > architectures and possibly depending on which file format (mach-o or ELF) you > are targeting. MIPS probably happens to use '$'. I know mach-o files use "L" > as the temporary symbol prefix, ELF tends to use '.'. Not sure where this > would be abstracted in LLVM or if it is just built into the assemblers > directly for each arch... If you can find out where this can be detected > within LLVM, we can make sure we don't use any temporary prefixes in symbol > names and work around this issue. We need to make sure that any functions we > generate and JIT up and insert into the program do not conflict with _any_ > symbol that could be in any system libraries or user binaries. This is why we > used '$' in the first place. > > Greg > >> On Oct 20, 2015, at 11:11 AM, Greg Clayton via lldb-dev >> <lldb-dev@lists.llvm.org> wrote: >> >> 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 >>> _______________________________________________ >>> lldb-dev mailing list >>> lldb-dev@lists.llvm.org >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev >> >> _______________________________________________ >> lldb-dev mailing list >> lldb-dev@lists.llvm.org >> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev > _______________________________________________ lldb-dev mailing list lldb-dev@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
