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

[Quentin Colombet]

Thanks Eric!

-Quentin

On Apr 14, 2014, at 10:24 AM, Eric Christopher <echristo at gmail.com> wrote:

> 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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>> 
>> 

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