[PATCH][MC] Emit an error if cfi_startproc is used before a symbol is defined

[Eric Christopher]

Still coming out from under Euro backlog. It's on my list :)

-eric

On Mon, Apr 14, 2014 at 10:23 AM, Quentin Colombet <qcolombet at apple.com> wrote:
> Ping?
>
> Thanks,
> -Quentin
>
> On Apr 9, 2014, at 4:06 PM, Quentin Colombet <qcolombet at apple.com> wrote:
>
> Hi Eric and Jim,
>
> @Eric, I do not know if you are the right person to review this, but compact
> frame information looks related enough to dwarf emission that I assume you
> know :).
>
> The attached patch fixes an assertion failure[1] in the assembler when a
> .cfi_startproc is used before a function (or more generally a symbol) is
> defined.
>
> Thanks for your reviews/feedbacks.
>
> ** Context **
>
> Currently the assembler crashes when emitting the compact unwind information
> if the input assembly file starts with a .cfi_startproc directive before any
> symbol has been defined.
>
> I am not a CFI expert, but that does not look right to me to use a
> .cfi_startproc directive without having started the related function!
>
>
> ** Proposed Solution **
>
> Issue a backend fatal error if a frame is started whereas no symbol is
> defined. Although this diagnostic method is not pretty, this is how all cfi
> related errors are handled (e.g., looks for No open frame).
>
> The patch also modifies a few test cases to define a function before
> .cfi_startproc is used.
> I.e., test cases like this:
> .cfi_startproc
>
> Looks like this now:
> _proc:
> .cfi_startproc
>
> If that does not make sense, please let me know!
>
> <rdar://problem/15939159>
>
> [1]
> Assertion failed: (Symbol), function MCSymbolRefExpr, file
> include/llvm/MC/MCExpr.h, line 273.
> 0  llvm-mc                  0x0000000109d85e3e
> llvm::sys::PrintStackTrace(__sFILE*) + 46
> 1  llvm-mc                  0x0000000109d8614b
> PrintStackTraceSignalHandler(void*) + 27
> 2  llvm-mc                  0x0000000109d864c8 SignalHandler(int) + 408
> 3  libsystem_platform.dylib 0x00007fff8f8895aa _sigtramp + 26
> 4  libsystem_platform.dylib 0x00007f9452c05338 _sigtramp + 3275210152
> 5  llvm-mc                  0x0000000109d8617b raise + 27
> 6  llvm-mc                  0x0000000109d86232 abort + 18
> 7  llvm-mc                  0x0000000109d86211 __assert_rtn + 129
> 8  llvm-mc                  0x0000000109d019bf
> llvm::MCSymbolRefExpr::MCSymbolRefExpr(llvm::MCSymbol const*,
> llvm::MCSymbolRefExpr::VariantKind, llvm::MCAsmInfo const*) + 143
> 9  llvm-mc                  0x0000000109d0081b
> llvm::MCSymbolRefExpr::MCSymbolRefExpr(llvm::MCSymbol const*,
> llvm::MCSymbolRefExpr::VariantKind, llvm::MCAsmInfo const*) + 43
> 10 llvm-mc                  0x0000000109cfda56
> llvm::MCSymbolRefExpr::Create(llvm::MCSymbol const*,
> llvm::MCSymbolRefExpr::VariantKind, llvm::MCContext&) + 134
> 11 llvm-mc                  0x0000000109b79df4
> llvm::MCSymbolRefExpr::Create(llvm::MCSymbol const*, llvm::MCContext&) + 36
> 12 llvm-mc                  0x0000000109d16f85
> llvm::MCStreamer::EmitSymbolValue(llvm::MCSymbol const*, unsigned int) + 69
> 13 llvm-mc                  0x0000000109ceb7ca (anonymous
> namespace)::FrameEmitterImpl::EmitCompactUnwind(llvm::MCStreamer&,
> llvm::MCDwarfFrameInfo const&) + 314
> 14 llvm-mc                  0x0000000109ceb2d6
> llvm::MCDwarfFrameEmitter::Emit(llvm::MCStreamer&, llvm::MCAsmBackend*,
> bool, bool) + 470
> 15 llvm-mc                  0x0000000109d1b1cf
> llvm::MCStreamer::EmitFrames(llvm::MCAsmBackend*, bool) + 95
> 16 llvm-mc                  0x0000000109d04152 (anonymous
> namespace)::MCMachOStreamer::FinishImpl() + 66
> 17 llvm-mc                  0x0000000109d1b2df llvm::MCStreamer::Finish() +
> 159
> 18 llvm-mc                  0x0000000109c30582 (anonymous
> namespace)::AsmParser::Run(bool, bool) + 2546
> 19 llvm-mc                  0x000000010995457c AssembleInput(char const*,
> llvm::Target const*, llvm::SourceMgr&, llvm::MCContext&, llvm::MCStreamer&,
> llvm::MCAsmInfo&, llvm::MCSubtargetInfo&, llvm::MCInstrInfo&) + 940
> 20 llvm-mc                  0x0000000109952461 main + 9457
> 21 libdyld.dylib            0x00007fff959e65fd start + 1
>
> Cheers,
> -Quentin
> <cfi_startproc.patch>
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