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diff --git a/docs/DebuggingJITedCode.html b/docs/DebuggingJITedCode.html deleted file mode 100644 index 92570f454c..0000000000 --- a/docs/DebuggingJITedCode.html +++ /dev/null @@ -1,171 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> -<html> -<head> - <title>Debugging JITed Code With GDB</title> - <link rel="stylesheet" href="llvm.css" type="text/css"> -</head> -<body> - -<div class="doc_title">Debugging JITed Code With GDB</div> -<ol> - <li><a href="#introduction">Introduction</a></li> - <li><a href="#quickstart">Quickstart</a></li> - <li><a href="#example">Example with clang and lli</a></li> -</ol> -<div class="doc_author">Written by Reid Kleckner</div> - -<!--=========================================================================--> -<div class="doc_section"><a name="introduction">Introduction</a></div> -<!--=========================================================================--> -<div class="doc_text"> - -<p>Without special runtime support, debugging dynamically generated code with -GDB (as well as most debuggers) can be quite painful. Debuggers generally read -debug information from the object file of the code, but for JITed code, there is -no such file to look for. -</p> - -<p>Depending on the architecture, this can impact the debugging experience in -different ways. For example, on most 32-bit x86 architectures, you can simply -compile with -fno-omit-framepointer for GCC and -fdisable-fp-elim for LLVM. -When GDB creates a backtrace, it can properly unwind the stack, but the stack -frames owned by JITed code have ??'s instead of the appropriate symbol name. -However, on Linux x86_64 in particular, GDB relies on the DWARF CFA debug -information to unwind the stack, so even if you compile your program to leave -the frame pointer untouched, GDB will usually be unable to unwind the stack past -any JITed code stack frames. -</p> - -<p>In order to communicate the necessary debug info to GDB, an interface for -registering JITed code with debuggers has been designed and implemented for -GDB and LLVM. At a high level, whenever LLVM generates new machine code, it -also generates an object file in memory containing the debug information. LLVM -then adds the object file to the global list of object files and calls a special -function (__jit_debug_register_code) marked noinline that GDB knows about. When -GDB attaches to a process, it puts a breakpoint in this function and loads all -of the object files in the global list. When LLVM calls the registration -function, GDB catches the breakpoint signal, loads the new object file from -LLVM's memory, and resumes the execution. In this way, GDB can get the -necessary debug information. -</p> - -<p>At the time of this writing, LLVM only supports architectures that use ELF -object files and it only generates symbols and DWARF CFA information. However, -it would be easy to add more information to the object file, so we don't need to -coordinate with GDB to get better debug information. -</p> -</div> - -<!--=========================================================================--> -<div class="doc_section"><a name="quickstart">Quickstart</a></div> -<!--=========================================================================--> -<div class="doc_text"> - -<p>In order to debug code JITed by LLVM, you need to install a recent version -of GDB. The interface was added on 2009-08-19, so you need a snapshot of GDB -more recent than that. Either download a snapshot of GDB or checkout CVS as -instructed <a href="http://www.gnu.org/software/gdb/current/">here</a>. Here -are the commands for doing a checkout and building the code: -</p> - -<pre class="doc_code"> -$ cvs -z 3 -d :pserver:anoncvs@sourceware.org:/cvs/src co gdb -$ mv src gdb # You probably don't want this checkout called "src". -$ cd gdb -$ ./configure --prefix="$GDB_INSTALL" -$ make -$ make install -</pre> - -<p>You can then use -jit-emit-debug in the LLVM command line arguments to enable -the interface. -</p> -</div> - -<!--=========================================================================--> -<div class="doc_section"><a name="example">Example with clang and lli</a></div> -<!--=========================================================================--> -<div class="doc_text"> - -<p>For example, consider debugging running lli on the following C code in -foo.c: -</p> - -<pre class="doc_code"> -#include <stdio.h> - -void foo() { - printf("%d\n", *(int*)NULL); // Crash here -} - -void bar() { - foo(); -} - -void baz() { - bar(); -} - -int main(int argc, char **argv) { - baz(); -} -</pre> - -<p>Here are the commands to run that application under GDB and print the stack -trace at the crash: -</p> - -<pre class="doc_code"> -# Compile foo.c to bitcode. You can use either clang or llvm-gcc with this -# command line. Both require -fexceptions, or the calls are all marked -# 'nounwind' which disables DWARF CFA info. -$ clang foo.c -fexceptions -emit-llvm -c -o foo.bc - -# Run foo.bc under lli with -jit-emit-debug. If you built lli in debug mode, -# -jit-emit-debug defaults to true. -$ $GDB_INSTALL/gdb --args lli -jit-emit-debug foo.bc -... - -# Run the code. -(gdb) run -Starting program: /tmp/gdb/lli -jit-emit-debug foo.bc -[Thread debugging using libthread_db enabled] - -Program received signal SIGSEGV, Segmentation fault. -0x00007ffff7f55164 in foo () - -# Print the backtrace, this time with symbols instead of ??. -(gdb) bt -#0 0x00007ffff7f55164 in foo () -#1 0x00007ffff7f550f9 in bar () -#2 0x00007ffff7f55099 in baz () -#3 0x00007ffff7f5502a in main () -#4 0x00000000007c0225 in llvm::JIT::runFunction(llvm::Function*, - std::vector<llvm::GenericValue, - std::allocator<llvm::GenericValue> > const&) () -#5 0x00000000007d6d98 in - llvm::ExecutionEngine::runFunctionAsMain(llvm::Function*, - std::vector<std::string, - std::allocator<std::string> > const&, char const* const*) () -#6 0x00000000004dab76 in main () -</pre> -</div> - -<p>As you can see, GDB can correctly unwind the stack and has the appropriate -function names. -</p> - -<!-- *********************************************************************** --> -<hr> -<address> - <a href="http://jigsaw.w3.org/css-validator/check/referer"><img - src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> - <a href="http://validator.w3.org/check/referer"><img - src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> - <a href="mailto:reid.kleckner@gmail.com">Reid Kleckner</a><br> - <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> - Last modified: $Date: 2009-01-01 23:10:51 -0800 (Thu, 01 Jan 2009) $ -</address> -</body> -</html> |