[PATCH] D67216: [cfi] Add flag to always generate .debug_frame

[David Candler via Phabricator via cfe-commits]

dcandler updated this revision to Diff 224581.
dcandler retitled this revision from "[cfi] Add flag to always generate call frame information" to "[cfi] Add flag to always generate .debug_frame".
dcandler edited the summary of this revision.
dcandler added reviewers: rengolin, joerg.
dcandler added a comment.
Herald added subscribers: jsji, MaskRay, kbarton, nemanjai.

I've modified the patch so that the new flag will ensure the cfi instructions are actually present to be emitted as well. I went ahead and renamed the flag -gdwarf-frame too, to better reflect that it's dealing with the debug information you'd otherwise get with -g, and is meant to specifically put the information in a .debug_frame section and not .eh_frame.

Currently, two things signal for need for cfi: exceptions (via the function's needsUnwindTableEntry()), and debug (via the machine module information's hasDebugInfo()). At frame lowering, both trigger the same thing. But when the assembly printer decides on which section to use, needsUnwindTableEntry() is checked first and triggers the need for .eh_frame, while hasDebugInfo() is checked afterwards for whether .debug_frame is needed. So .debug_frame is only present when any level of debug is requested, and no functions need unwinding for exceptions.

It wouldn't be appropriate to change either needsUnwindTableEntry() or hasDebugInfo(), so I've added a check for my flag alongside them. Because the same logic is used in multiple places, I've wrapped all three checks into one function to try and clean things up slightly. When deciding on which section to emit, the new flag means .debug_frame is produced instead of nothing. If .eh_frame would have been needed, rather than replace it, the new flag simply emits both .debug_frame and .eh_frame.

The end result is that -gdwarf-frame should only provide a .debug_frame section as additional information, without otherwise modifying anything. The existing -funwind-tables (and -fasynchronous-unwind-tables) flag can be used to provide similar information, but because it takes the exception angle, it alters function attributes and ultimately produces .eh_frame instead.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67216/new/

https://reviews.llvm.org/D67216

Files:
  clang/include/clang/Basic/CodeGenOptions.def
  clang/include/clang/Driver/Options.td
  clang/lib/CodeGen/BackendUtil.cpp
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/lib/Frontend/CompilerInvocation.cpp
  clang/test/Driver/gdwarf-frame.c
  llvm/include/llvm/CodeGen/CommandFlags.inc
  llvm/include/llvm/CodeGen/MachineFunction.h
  llvm/include/llvm/Target/TargetOptions.h
  llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
  llvm/lib/CodeGen/AsmPrinter/DwarfCFIException.cpp
  llvm/lib/CodeGen/CFIInstrInserter.cpp
  llvm/lib/CodeGen/MachineFunction.cpp
  llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
  llvm/lib/Target/ARC/ARCRegisterInfo.cpp
  llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp
  llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
  llvm/lib/Target/X86/X86FrameLowering.cpp
  llvm/lib/Target/X86/X86InstrInfo.cpp
  llvm/lib/Target/XCore/XCoreRegisterInfo.cpp
  llvm/test/CodeGen/ARM/dwarf-frame.ll

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