You've already forked linux-packaging-mono
Imported Upstream version 5.18.0.207
Former-commit-id: 3b152f462918d427ce18620a2cbe4f8b79650449
This commit is contained in:
Xamarin Public Jenkins (auto-signing)
parent
8e12397d70
commit
eb85e2fc17
143
external/llvm/docs/DebuggingJITedCode.rst
vendored
143
external/llvm/docs/DebuggingJITedCode.rst
vendored
@ -1,143 +0,0 @@
|
||||
==============================
|
||||
Debugging JIT-ed Code With GDB
|
||||
==============================
|
||||
|
||||
Background
|
||||
==========
|
||||
|
||||
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.
|
||||
|
||||
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 MCJIT. At a high level, whenever MCJIT generates new machine code,
|
||||
it does so in an in-memory object file that contains the debug information in
|
||||
DWARF format. MCJIT then adds this in-memory object file to a global list of
|
||||
dynamically generated 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 MCJIT calls the registration
|
||||
function, GDB catches the breakpoint signal, loads the new object file from
|
||||
the inferior's memory, and resumes the execution. In this way, GDB can get the
|
||||
necessary debug information.
|
||||
|
||||
GDB Version
|
||||
===========
|
||||
|
||||
In order to debug code JIT-ed by LLVM, you need GDB 7.0 or newer, which is
|
||||
available on most modern distributions of Linux. The version of GDB that
|
||||
Apple ships with Xcode has been frozen at 6.3 for a while. LLDB may be a
|
||||
better option for debugging JIT-ed code on Mac OS X.
|
||||
|
||||
|
||||
Debugging MCJIT-ed code
|
||||
=======================
|
||||
|
||||
The emerging MCJIT component of LLVM allows full debugging of JIT-ed code with
|
||||
GDB. This is due to MCJIT's ability to use the MC emitter to provide full
|
||||
DWARF debugging information to GDB.
|
||||
|
||||
Note that lli has to be passed the ``-use-mcjit`` flag to JIT the code with
|
||||
MCJIT instead of the old JIT.
|
||||
|
||||
Example
|
||||
-------
|
||||
|
||||
Consider the following C code (with line numbers added to make the example
|
||||
easier to follow):
|
||||
|
||||
..
|
||||
FIXME:
|
||||
Sphinx has the ability to automatically number these lines by adding
|
||||
:linenos: on the line immediately following the `.. code-block:: c`, but
|
||||
it looks like garbage; the line numbers don't even line up with the
|
||||
lines. Is this a Sphinx bug, or is it a CSS problem?
|
||||
|
||||
.. code-block:: c
|
||||
|
||||
1 int compute_factorial(int n)
|
||||
2 {
|
||||
3 if (n <= 1)
|
||||
4 return 1;
|
||||
5
|
||||
6 int f = n;
|
||||
7 while (--n > 1)
|
||||
8 f *= n;
|
||||
9 return f;
|
||||
10 }
|
||||
11
|
||||
12
|
||||
13 int main(int argc, char** argv)
|
||||
14 {
|
||||
15 if (argc < 2)
|
||||
16 return -1;
|
||||
17 char firstletter = argv[1][0];
|
||||
18 int result = compute_factorial(firstletter - '0');
|
||||
19
|
||||
20 // Returned result is clipped at 255...
|
||||
21 return result;
|
||||
22 }
|
||||
|
||||
Here is a sample command line session that shows how to build and run this
|
||||
code via ``lli`` inside GDB:
|
||||
|
||||
.. code-block:: bash
|
||||
|
||||
$ $BINPATH/clang -cc1 -O0 -g -emit-llvm showdebug.c
|
||||
$ gdb --quiet --args $BINPATH/lli -use-mcjit showdebug.ll 5
|
||||
Reading symbols from $BINPATH/lli...done.
|
||||
(gdb) b showdebug.c:6
|
||||
No source file named showdebug.c.
|
||||
Make breakpoint pending on future shared library load? (y or [n]) y
|
||||
Breakpoint 1 (showdebug.c:6) pending.
|
||||
(gdb) r
|
||||
Starting program: $BINPATH/lli -use-mcjit showdebug.ll 5
|
||||
[Thread debugging using libthread_db enabled]
|
||||
|
||||
Breakpoint 1, compute_factorial (n=5) at showdebug.c:6
|
||||
6 int f = n;
|
||||
(gdb) p n
|
||||
$1 = 5
|
||||
(gdb) p f
|
||||
$2 = 0
|
||||
(gdb) n
|
||||
7 while (--n > 1)
|
||||
(gdb) p f
|
||||
$3 = 5
|
||||
(gdb) b showdebug.c:9
|
||||
Breakpoint 2 at 0x7ffff7ed404c: file showdebug.c, line 9.
|
||||
(gdb) c
|
||||
Continuing.
|
||||
|
||||
Breakpoint 2, compute_factorial (n=1) at showdebug.c:9
|
||||
9 return f;
|
||||
(gdb) p f
|
||||
$4 = 120
|
||||
(gdb) bt
|
||||
#0 compute_factorial (n=1) at showdebug.c:9
|
||||
#1 0x00007ffff7ed40a9 in main (argc=2, argv=0x16677e0) at showdebug.c:18
|
||||
#2 0x3500000001652748 in ?? ()
|
||||
#3 0x00000000016677e0 in ?? ()
|
||||
#4 0x0000000000000002 in ?? ()
|
||||
#5 0x0000000000d953b3 in llvm::MCJIT::runFunction (this=0x16151f0, F=0x1603020, ArgValues=...) at /home/ebenders_test/llvm_svn_rw/lib/ExecutionEngine/MCJIT/MCJIT.cpp:161
|
||||
#6 0x0000000000dc8872 in llvm::ExecutionEngine::runFunctionAsMain (this=0x16151f0, Fn=0x1603020, argv=..., envp=0x7fffffffe040)
|
||||
at /home/ebenders_test/llvm_svn_rw/lib/ExecutionEngine/ExecutionEngine.cpp:397
|
||||
#7 0x000000000059c583 in main (argc=4, argv=0x7fffffffe018, envp=0x7fffffffe040) at /home/ebenders_test/llvm_svn_rw/tools/lli/lli.cpp:324
|
||||
(gdb) finish
|
||||
Run till exit from #0 compute_factorial (n=1) at showdebug.c:9
|
||||
0x00007ffff7ed40a9 in main (argc=2, argv=0x16677e0) at showdebug.c:18
|
||||
18 int result = compute_factorial(firstletter - '0');
|
||||
Value returned is $5 = 120
|
||||
(gdb) p result
|
||||
$6 = 23406408
|
||||
(gdb) n
|
||||
21 return result;
|
||||
(gdb) p result
|
||||
$7 = 120
|
||||
(gdb) c
|
||||
Continuing.
|
||||
|
||||
Program exited with code 0170.
|
||||
(gdb)
|
||||
Reference in New Issue
Block a user