Re: [PATCH 4/7] Step over fork/vfork syscall insn in gdbserver

[Luis Machado <lgustavo@codesourcery.com>]

On 02/26/2016 11:03 AM, Yao Qi wrote:
> We can also extend disp-step-syscall.exp to test GDBserver step over
> breakpoint on syscall instruction.  That is, we set a breakpoint
> with a false condition on syscall instruction, so that GDBserver will
> step over it.
>
> This test triggers a GDBserver internal error, which can be fixed by
> this series.
>
> (gdb) PASS: gdb.base/disp-step-syscall.exp: fork: break cond on target: break on syscall insns
> continue^M
> Continuing.^M
> Remote connection closed^M
> (gdb) FAIL: gdb.base/disp-step-syscall.exp: fork: break cond on target: continue to fork again
>
> In GDBserver, there is an internal error,
>
> /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:1922: A problem internal to GDBserver has been detected.
> unsuspend LWP 25554, suspended=-1
>
> the simplified reproducer is like,
>
> $ ./gdb ./testsuite/outputs/gdb.base/disp-step-syscall/disp-step-fork
> (gdb) b main
> (gdb) c
> (gdb) disassemble fork // in order to find the address of insn 'syscall'
> ....
>     0x00007ffff7ad6023 <+179>:	syscall
> (gdb) b *0x00007ffff7ad6023 if main == 0
> (gdb) c
>
> gdb/testsuite:
>
> 2016-02-26  Yao Qi  <yao.qi@linaro.org>
>
> 	* gdb.base/disp-step-syscall.exp (break_cond_on_syscall): New.
> 	If target supports condition evaluation on target, invoke
> 	break_cond_on_syscall for fork and vfork.
> ---
>   gdb/testsuite/gdb.base/disp-step-syscall.exp | 57 ++++++++++++++++++++++++++++
>   1 file changed, 57 insertions(+)
>
> diff --git a/gdb/testsuite/gdb.base/disp-step-syscall.exp b/gdb/testsuite/gdb.base/disp-step-syscall.exp
> index 3cf436d..9ecf2a5 100644
> --- a/gdb/testsuite/gdb.base/disp-step-syscall.exp
> +++ b/gdb/testsuite/gdb.base/disp-step-syscall.exp
> @@ -168,5 +168,62 @@ proc disp_step_cross_syscall { syscall } {
>       }
>   }
>
> +# Set a breakpoint with a condition that evals false on syscall
> +# instruction.  In fact, it tests GDBserver steps over syscall
> +# instruction.
> +
> +proc break_cond_on_syscall { syscall } {
> +    with_test_prefix "break cond on target : $syscall" {
> +	set testfile "disp-step-$syscall"
> +
> +	set ret [setup $syscall]
> +
> +	set syscall_insn_addr [lindex $ret 0]
> +	set syscall_insn_next_addr [lindex $ret 1]
> +	if { $syscall_insn_addr == -1 } {
> +	    return -1
> +	}
> +
> +	gdb_test "continue" "Continuing\\..*Breakpoint \[0-9\]+, (.* in |__libc_|)$syscall \\(\\).*" \
> +	    "continue to $syscall"
> +	# Delete breakpoint syscall insns to avoid interference to other syscalls.
> +	delete_breakpoints

"... interference with ..."