[llvm-bugs] [Bug 50936] New: lldb step over glibc dlopen fails (__GI__dl_catch_exception or runs away)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50936

            Bug ID: 50936
           Summary: lldb step over glibc dlopen fails
                    (__GI__dl_catch_exception or runs away)
           Product: lldb
           Version: 12.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: lldb-dev at lists.llvm.org
          Reporter: rprichard at google.com
                CC: jdevlieghere at apple.com, llvm-bugs at lists.llvm.org

Using glibc (specifically gLinux aka Debian), LLDB is unable to step over
certain dlopen calls.

In one situation, the library was part of the initial set of needed DSOs, and
LLDB fails with a __GI__dl_catch_exception error. In another situation, the
library isn't loaded already, and when dlopen loads it, LLDB fails to stop
after the dlopen call (and runs to process exit).

Both problems reproduce with either LLVM 12.0.0
(clang+llvm-12.0.0-x86_64-linux-gnu-ubuntu-20.04) or with an upstream Clang and
LLDB that I built today from origin/main.

Test case:

$ cat >test.c <<EOF
#include <dlfcn.h>
int main(void) {
  void* ptr;
  dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
  dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
  dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
  dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
  dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
  dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
  return 0;
}
EOF

## Situation 1: __GI__dl_catch_exception (link with -lm)

$ /x/clang12/bin/clang -g test.c -ldl -lm
$ /x/clang12/bin/lldb a.out
(lldb) target create "a.out"
Current executable set to '/x/mess/a.out' (x86_64).
(lldb) b main
Breakpoint 1: where = a.out`main + 15 at test.c:4:3, address =
0x000000000040113f
(lldb) run
Process 282393 launched: '/x/mess/a.out' (x86_64)
Process 282393 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x000000000040113f a.out`main at test.c:4:3
   1    #include <dlfcn.h>
   2    int main(void) {
   3      void* ptr;
-> 4      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   5      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   6      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   7      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
(lldb) n
Process 282393 stopped
* thread #1, name = 'a.out', stop reason = step over
    frame #0: 0x00007ffff7dca260
libc.so.6`__GI__dl_catch_exception(exception=0x00007fffffffda40,
operate=0x00007ffff7fe5ca0, args=0x00007fffffffda60) at
dl-error-skeleton.c:209:18

## Situation 2: process runs away when dlopen loads libm.so.6 (don't link with
-lm)

$ /x/clang12/bin/clang -g test.c -ldl
$ /x/clang12/bin/lldb a.out
(lldb) target create "a.out"
Current executable set to '/x/mess/a.out' (x86_64).
(lldb) b test.c:5
Breakpoint 1: where = a.out`main + 35 at test.c:5:3, address =
0x0000000000401153
(lldb) run
Process 283170 launched: '/x/mess/a.out' (x86_64)
Process 283170 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000401153 a.out`main at test.c:5:3
   2    int main(void) {
   3      void* ptr;
   4      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
-> 5      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   6      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   7      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
   8      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
(lldb) n
Process 283170 stopped
* thread #1, name = 'a.out', stop reason = step over
    frame #0: 0x0000000000401167 a.out`main at test.c:6:3
   3      void* ptr;
   4      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   5      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
-> 6      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   7      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
   8      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
   9      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
(lldb) n
Process 283170 stopped
* thread #1, name = 'a.out', stop reason = step over
    frame #0: 0x000000000040117b a.out`main at test.c:7:3
   4      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   5      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
   6      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL | RTLD_NOLOAD);
-> 7      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
   8      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
   9      dlopen("libm.so.6", RTLD_NOW | RTLD_LOCAL);
   10     return 0;
(lldb) n
Process 283170 exited with status = 0 (0x00000000)

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