Debug info broken for ASan-instrumented binaries

Hi,

I noticed that debugging of AddressSanitizer-instrumented debug binaries
is basically impossible since all the symbols are optimized out. It looks like
there is something wrong with debug info. I'm getting the same behavior
on 3.4 and trunk. Interestingly it works for -fsanitize=undefined. Is this a known
issue? There are several related bugs but they are fixed already, e.g.
http://llvm.org/bugs/show_bug.cgi?id=11818

# cat UnitAsanStackOOB.cpp
int main()
{
    const int len = 10;
    char buffer[len];
    char *p = &buffer[0];
    p[len] = 1;
    return 0;
}

# clang++ -g -o oob_trunk_add -fsanitize=address UnitAsanStackOOB.cpp
# gdb oob_trunk_add
GNU gdb (GDB) 7.5.1
Reading symbols from /local/build/git5/sys/src/clang/AddressSanitizer/test/oob_trunk_add...done.
(gdb) b main
Breakpoint 1 at 0x495a4a: file UnitAsanStackOOB.cpp, line 3.
(gdb) run
Starting program: /local/build/git5/sys/src/clang/AddressSanitizer/test/oob_trunk_add
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Breakpoint 1, main () at UnitAsanStackOOB.cpp:3
3 const int len = 10;
(gdb) n
5 char *p = &buffer[0];
(gdb) n
6 p[len] = 1;
(gdb) p p
$1 = <optimized out>
(gdb) p len
$2 = <optimized out>

# clang++ -g -o oob_trunk_und -fsanitize=undefined UnitAsanStackOOB.cpp
# gdb oob_trunk_und
GNU gdb (GDB) 7.5.1
(gdb) b main
Breakpoint 1 at 0x426280: file UnitAsanStackOOB.cpp, line 2.
(gdb) run
Starting program: /local/build/git5/sys/src/clang/AddressSanitizer/test/oob_trunk_und
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Breakpoint 1, main () at UnitAsanStackOOB.cpp:2
2 {
(gdb) n
3 const int len = 10;
(gdb) n
5 char *p = &buffer[0];
(gdb) n
6 p[len] = 1;
(gdb) p p
$1 = 0x7fffffff975e ""
(gdb) p len
$2 = 10

# clang++ -v
clang version 3.5.0 (trunk 204863)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib64/gcc/x86_64-suse-linux/4.3
Selected GCC installation: /usr/lib64/gcc/x86_64-suse-linux/4.3
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

Best regards,
Martin

+samsonov@

Hi Martin,

Sorry for the late response.
This is tracked in https://code.google.com/p/address-sanitizer/issues/detail?id=235
In short - there is a bug in LLVM DWARF generation, that fires rarely on a regular C++ code (especially with -O0),
but breaks debug info if we instrument the code with ASan. I’ve looked at this issue and had some ideas
about how this should be fixed, but didn’t finish the work yet.

Hi Martin,

Sorry for the late response.
This is tracked in
https://code.google.com/p/address-sanitizer/issues/detail?id=235
In short - there is a bug in LLVM DWARF generation, that fires rarely on a
regular C++ code (especially with -O0),
but breaks debug info if we instrument the code with ASan. I've looked at
this issue and had some ideas
about how this should be fixed, but didn't finish the work yet.

Yeah, let's pick this back up. Can you ping the original thread where
you started looking into this?

-eric