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feature, either build the JIT in debug mode to enable it by default or pass
-jit-emit-debug to lli.
Right now, the only debug information that this communicates to GDB is call
frame information, since it's already being generated to support exceptions in
the JIT. Eventually, when DWARF generation isn't tied so tightly to AsmPrinter,
it will be easy to push that information to GDB through this interface.
Here's a step-by-step breakdown of how the feature works:
- The JIT generates the machine code and DWARF call frame info
(.eh_frame/.debug_frame) for a function into memory.
- The JIT copies that info into an in-memory ELF file with a symbol for the
function.
- The JIT creates a code entry pointing to the ELF buffer and adds it to a
linked list hanging off of a global descriptor at a special symbol that GDB
knows about.
- The JIT calls a function marked noinline that GDB knows about and has put an
internal breakpoint in.
- GDB catches the breakpoint and reads the global descriptor to look for new
code.
- When sees there is new code, it reads the ELF from the inferior's memory and
adds it to itself as an object file.
- The JIT continues, and the next time we stop the program, we are able to
produce a proper backtrace.
Consider running the following program through the JIT:
#include <stdio.h>
void baz(short z) {
long w = z + 1;
printf("%d, %x\n", w, *((int*)NULL)); // SEGFAULT here
}
void bar(short y) {
int z = y + 1;
baz(z);
}
void foo(char x) {
short y = x + 1;
bar(y);
}
int main(int argc, char** argv) {
char x = 1;
foo(x);
}
Here is a backtrace before this patch:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x2aaaabdfbd10 (LWP 25476)]
0x00002aaaabe7d1a8 in ?? ()
(gdb) bt
#0 0x00002aaaabe7d1a8 in ?? ()
#1 0x0000000000000003 in ?? ()
#2 0x0000000000000004 in ?? ()
#3 0x00032aaaabe7cfd0 in ?? ()
#4 0x00002aaaabe7d12c in ?? ()
#5 0x00022aaa00000003 in ?? ()
#6 0x00002aaaabe7d0aa in ?? ()
#7 0x01000002abe7cff0 in ?? ()
#8 0x00002aaaabe7d02c in ?? ()
#9 0x0100000000000001 in ?? ()
#10 0x00000000014388e0 in ?? ()
#11 0x00007fff00000001 in ?? ()
#12 0x0000000000b870a2 in llvm::JIT::runFunction (this=0x1405b70,
F=0x14024e0, ArgValues=@0x7fffffffe050)
at /home/rnk/llvm-gdb/lib/ExecutionEngine/JIT/JIT.cpp:395
#13 0x0000000000baa4c5 in llvm::ExecutionEngine::runFunctionAsMain
(this=0x1405b70, Fn=0x14024e0, argv=@0x13f06f8, envp=0x7fffffffe3b0)
at /home/rnk/llvm-gdb/lib/ExecutionEngine/ExecutionEngine.cpp:377
#14 0x00000000007ebd52 in main (argc=2, argv=0x7fffffffe398,
envp=0x7fffffffe3b0) at /home/rnk/llvm-gdb/tools/lli/lli.cpp:208
And a backtrace after this patch:
Program received signal SIGSEGV, Segmentation fault.
0x00002aaaabe7d1a8 in baz ()
(gdb) bt
#0 0x00002aaaabe7d1a8 in baz ()
#1 0x00002aaaabe7d12c in bar ()
#2 0x00002aaaabe7d0aa in foo ()
#3 0x00002aaaabe7d02c in main ()
#4 0x0000000000b870a2 in llvm::JIT::runFunction (this=0x1405b70,
F=0x14024e0, ArgValues=...)
at /home/rnk/llvm-gdb/lib/ExecutionEngine/JIT/JIT.cpp:395
#5 0x0000000000baa4c5 in llvm::ExecutionEngine::runFunctionAsMain
(this=0x1405b70, Fn=0x14024e0, argv=..., envp=0x7fffffffe3c0)
at /home/rnk/llvm-gdb/lib/ExecutionEngine/ExecutionEngine.cpp:377
#6 0x00000000007ebd52 in main (argc=2, argv=0x7fffffffe3a8,
envp=0x7fffffffe3c0) at /home/rnk/llvm-gdb/tools/lli/lli.cpp:208
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82418 91177308-0d34-0410-b5e6-96231b3b80d8
147 lines
6.3 KiB
C++
147 lines
6.3 KiB
C++
//===-- llvm/Target/TargetOptions.h - Target Options ------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines command line option flags that are shared across various
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// targets.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TARGET_TARGETOPTIONS_H
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#define LLVM_TARGET_TARGETOPTIONS_H
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namespace llvm {
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// Possible float ABI settings. Used with FloatABIType in TargetOptions.h.
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namespace FloatABI {
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enum ABIType {
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Default, // Target-specific (either soft of hard depending on triple, etc).
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Soft, // Soft float.
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Hard // Hard float.
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};
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}
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/// PrintMachineCode - This flag is enabled when the -print-machineinstrs
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/// option is specified on the command line, and should enable debugging
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/// output from the code generator.
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extern bool PrintMachineCode;
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/// NoFramePointerElim - This flag is enabled when the -disable-fp-elim is
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/// specified on the command line. If the target supports the frame pointer
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/// elimination optimization, this option should disable it.
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extern bool NoFramePointerElim;
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/// LessPreciseFPMAD - This flag is enabled when the
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/// -enable-fp-mad is specified on the command line. When this flag is off
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/// (the default), the code generator is not allowed to generate mad
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/// (multiply add) if the result is "less precise" than doing those operations
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/// individually.
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extern bool LessPreciseFPMADOption;
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extern bool LessPreciseFPMAD();
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/// NoExcessFPPrecision - This flag is enabled when the
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/// -disable-excess-fp-precision flag is specified on the command line. When
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/// this flag is off (the default), the code generator is allowed to produce
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/// results that are "more precise" than IEEE allows. This includes use of
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/// FMA-like operations and use of the X86 FP registers without rounding all
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/// over the place.
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extern bool NoExcessFPPrecision;
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/// UnsafeFPMath - This flag is enabled when the
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/// -enable-unsafe-fp-math flag is specified on the command line. When
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/// this flag is off (the default), the code generator is not allowed to
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/// produce results that are "less precise" than IEEE allows. This includes
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/// use of X86 instructions like FSIN and FCOS instead of libcalls.
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/// UnsafeFPMath implies FiniteOnlyFPMath and LessPreciseFPMAD.
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extern bool UnsafeFPMath;
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/// FiniteOnlyFPMath - This returns true when the -enable-finite-only-fp-math
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/// option is specified on the command line. If this returns false (default),
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/// the code generator is not allowed to assume that FP arithmetic arguments
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/// and results are never NaNs or +-Infs.
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extern bool FiniteOnlyFPMathOption;
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extern bool FiniteOnlyFPMath();
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/// HonorSignDependentRoundingFPMath - This returns true when the
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/// -enable-sign-dependent-rounding-fp-math is specified. If this returns
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/// false (the default), the code generator is allowed to assume that the
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/// rounding behavior is the default (round-to-zero for all floating point to
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/// integer conversions, and round-to-nearest for all other arithmetic
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/// truncations). If this is enabled (set to true), the code generator must
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/// assume that the rounding mode may dynamically change.
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extern bool HonorSignDependentRoundingFPMathOption;
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extern bool HonorSignDependentRoundingFPMath();
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/// UseSoftFloat - This flag is enabled when the -soft-float flag is specified
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/// on the command line. When this flag is on, the code generator will
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/// generate libcalls to the software floating point library instead of
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/// target FP instructions.
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extern bool UseSoftFloat;
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/// FloatABIType - This setting is set by -float-abi=xxx option is specfied
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/// on the command line. This setting may either be Default, Soft, or Hard.
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/// Default selects the target's default behavior. Soft selects the ABI for
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/// UseSoftFloat, but does not inidcate that FP hardware may not be used.
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/// Such a combination is unfortunately popular (e.g. arm-apple-darwin).
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/// Hard presumes that the normal FP ABI is used.
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extern FloatABI::ABIType FloatABIType;
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/// NoZerosInBSS - By default some codegens place zero-initialized data to
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/// .bss section. This flag disables such behaviour (necessary, e.g. for
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/// crt*.o compiling).
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extern bool NoZerosInBSS;
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/// DwarfExceptionHandling - This flag indicates that Dwarf exception
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/// information should be emitted.
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extern bool DwarfExceptionHandling;
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/// SjLjExceptionHandling - This flag indicates that SJLJ exception
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/// information should be emitted.
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extern bool SjLjExceptionHandling;
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/// JITEmitDebugInfo - This flag indicates that the JIT should try to emit
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/// debug information and notify a debugger about it.
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extern bool JITEmitDebugInfo;
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/// JITEmitDebugInfoToDisk - This flag indicates that the JIT should write
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/// the object files generated by the JITEmitDebugInfo flag to disk. This
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/// flag is hidden and is only for debugging the debug info.
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extern bool JITEmitDebugInfoToDisk;
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/// UnwindTablesMandatory - This flag indicates that unwind tables should
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/// be emitted for all functions.
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extern bool UnwindTablesMandatory;
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/// PerformTailCallOpt - This flag is enabled when -tailcallopt is specified
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/// on the commandline. When the flag is on, the target will perform tail call
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/// optimization (pop the caller's stack) providing it supports it.
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extern bool PerformTailCallOpt;
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/// StackAlignment - Override default stack alignment for target.
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extern unsigned StackAlignment;
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/// RealignStack - This flag indicates, whether stack should be automatically
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/// realigned, if needed.
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extern bool RealignStack;
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/// DisableJumpTables - This flag indicates jump tables should not be
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/// generated.
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extern bool DisableJumpTables;
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/// EnableFastISel - This flag enables fast-path instruction selection
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/// which trades away generated code quality in favor of reducing
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/// compile time.
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extern bool EnableFastISel;
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/// StrongPHIElim - This flag enables more aggressive PHI elimination
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/// wth earlier copy coalescing.
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extern bool StrongPHIElim;
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} // End llvm namespace
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#endif
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