Re: [PATCH][gdb/testsuite] Work around skip_prologue problems in gdb.threads/process-dies-while-detaching.exp

[Tom de Vries <tdevries@suse.de>]

On 10/29/21 9:24 PM, Tom de Vries via Gdb-patches wrote:
> Hi,
> 
> On powerpc64le-linux, I run into:
> ...
> [Inferior 1 (process 5156) exited normally]^M
> (gdb) FAIL: gdb.threads/process-dies-while-detaching.exp: single-process: \
>   detach: detach: continue to breakpoint: _exit (the program exited)
> ...
> 
> What happens is the following:
> - a breakpoint is set on _exit,
> - a continue is issued
> - the continue is supposed to hit the breakpoint, but instead
>   the program exits.
> 
> I traced this down to the breakpoint on _exit being set too far from function
> entry.  This is caused by the skip_prologue function (in rs6000-tdep.c)
> optimistically ignoring insns it doesn't recognize.  In particular, it walks
> past the system call instruction "sc" which initiates the actual exit.
> 
> While this needs fixing,

Filed here: https://sourceware.org/bugzilla/show_bug.cgi?id=28527 .

Submitted patch here:
https://sourceware.org/pipermail/gdb-patches/2021-November/183016.html .

Thanks,
- Tom

> we don't want to be testing this behaviour in this
> test-case.
> 
> [ Initially I tried to fix it by setting a breakpoint on "*_exit" instead, but
> that one only sets one location.  The breakpoint on "_exit" sets two
> locations, one in /lib64/libc.so.6 and one in /lib64/ld64.so.2.  I tried on
> x86_64 and there the breakpoint on "*_exit" mapped to the /lib64/libc.so.6
> location, and the test-case passed.  But on powerpc it mapped to the
> /lib64/ld64.so.2 location and I still got the same failures. ]
> 
> Fix this by setting two breakpoints on the calls to _exit and exit instead.
> 
> Tested on x86_64-linux and powerpc64le-linux.
> 
> Any comments?
> 
> Thanks,
> - Tom
> 
> [gdb/testsuite] Work around skip_prologue problems in gdb.threads/process-dies-while-detaching.exp
> 
> ---
>  gdb/testsuite/gdb.threads/process-dies-while-detaching.c   | 4 ++--
>  gdb/testsuite/gdb.threads/process-dies-while-detaching.exp | 8 ++++++--
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.threads/process-dies-while-detaching.c b/gdb/testsuite/gdb.threads/process-dies-while-detaching.c
> index 502b4622614..c4c0b0a648b 100644
> --- a/gdb/testsuite/gdb.threads/process-dies-while-detaching.c
> +++ b/gdb/testsuite/gdb.threads/process-dies-while-detaching.c
> @@ -46,7 +46,7 @@ void *
>  thread_function (void *arg)
>  {
>    pthread_barrier_wait (&start_threads_barrier);
> -  _exit (0);
> +  _exit (0); /* Exit in thread.  */
>  }
>  
>  /* The fork child's entry point.  */
> @@ -63,7 +63,7 @@ child_function (void)
>      pthread_create (&threads[i], NULL, thread_function, NULL);
>    pthread_barrier_wait (&start_threads_barrier);
>  
> -  exit (0);
> +  exit (0); /* Exit in child.  */
>  }
>  
>  /* This is defined by the .exp file if testing the multi-process
> diff --git a/gdb/testsuite/gdb.threads/process-dies-while-detaching.exp b/gdb/testsuite/gdb.threads/process-dies-while-detaching.exp
> index cabbc4faacc..bbf1e0e6740 100644
> --- a/gdb/testsuite/gdb.threads/process-dies-while-detaching.exp
> +++ b/gdb/testsuite/gdb.threads/process-dies-while-detaching.exp
> @@ -126,8 +126,12 @@ proc detach_and_expect_exit {inf_output_re test} {
>  # Run to _exit in the child.
>  
>  proc continue_to_exit_bp {} {
> -    gdb_breakpoint "_exit" temporary
> -    gdb_continue_to_breakpoint "_exit" ".*_exit.*"
> +    set line [gdb_get_line_number "Exit in child"]
> +    gdb_breakpoint $line temporary
> +    set line [gdb_get_line_number "Exit in thread"]
> +    gdb_breakpoint $line temporary
> +    gdb_continue_to_breakpoint "exit" ".*exit.*"
> +    delete_breakpoints
>  }
>  
>  # If testing single-process, simply detach from the process.
>