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
llvm-svn: 82418
Eliminate the PersonalityPrefix/Suffix & NeedsIndirectEncoding
fields from MAI: they aren't part of the asm syntax, they are
related to the structure of the object file.
To replace their functionality, add a new
TLOF::getSymbolForDwarfGlobalReference method which asks targets
to decide how to reference a global from EH in a pc-relative way.
The default implementation just returns the symbol. The default
darwin implementation references the symbol through an indirect
$non_lazy_ptr stub. The bizarro x86-64 darwin specialization
handles the weird "foo@GOTPCREL+4" hack.
DwarfException.cpp now uses this to emit the reference to the
symbol in the right way, and this also eliminates another
horrible hack from DwarfException.cpp:
- if (strcmp(MAI->getPersonalitySuffix(), "+4@GOTPCREL"))
- O << "-" << MAI->getPCSymbol();
llvm-svn: 81991
full AsmPrinter, and change TargetRegistry to keep track
of registered MCInstPrinters.
llvm-mc is still linking in the entire
target foo to get the code emitter stuff, but this is an
important step in the right direction.
llvm-svn: 81754
that things like .word can be parsed as target specific. Moved parsing .word
out of AsmParser.cpp into X86AsmParser.cpp as it is 2 bytes on X86 and 4 bytes
for other targets that support the .word directive.
llvm-svn: 81461
all disassemblers.
Modified the MemoryObject to support 64-bit address
spaces, regardless of the LLVM process's address
width.
Modified the Target class to allow extraction of a
MCDisassembler.
llvm-svn: 81392
avoid reloads by reusing clobbered registers.
This was causing issues in 256.bzip2 when compiled with PIC for
a while (starting at r78217), though the problem has since been masked.
llvm-svn: 80872
encodings.
- Make some of the values emitted by the FDEs dependent upon the pointer
size. This is in line with how GCC does things. And it has the benefit of
working for Darwin in 64-bit mode now.
llvm-svn: 80428
support unaligned mem access only for certain types. (Should it be size
instead?)
ARM v7 supports unaligned access for i16 and i32, some v6 variants support it
as well.
llvm-svn: 79127
libcall. Take advantage of this in the ARM backend to rectify broken
choice of CC when hard float is in effect. PIC16 may want to see if
it could be of use in MakePIC16Libcall, which works unchanged.
Patch by Sandeep!
llvm-svn: 79033
TargetAsmInfo. This eliminates a dependency on TargetMachine.h from
TargetRegistry.h, which technically was a layering violation.
- Clients probably can only sensibly pass in the same TargetAsmInfo as the
TargetMachine has, but there are only limited clients of this API.
llvm-svn: 78928
x86_64-apple-darwin10.
--- Reverse-merging r78895 into '.':
U test/CodeGen/PowerPC/2008-12-12-EH.ll
U lib/Target/DarwinTargetAsmInfo.cpp
--- Reverse-merging r78892 into '.':
U include/llvm/Target/DarwinTargetAsmInfo.h
U lib/Target/X86/X86TargetAsmInfo.cpp
U lib/Target/X86/X86TargetAsmInfo.h
U lib/Target/ARM/ARMTargetAsmInfo.h
U lib/Target/ARM/ARMTargetMachine.cpp
U lib/Target/ARM/ARMTargetAsmInfo.cpp
U lib/Target/PowerPC/PPCTargetAsmInfo.cpp
U lib/Target/PowerPC/PPCTargetAsmInfo.h
U lib/Target/PowerPC/PPCTargetMachine.cpp
G lib/Target/DarwinTargetAsmInfo.cpp
llvm-svn: 78919
