Re: [PATCH] Fix build with latest GCC 9.0 tree

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2018-12-17 14:30, Dimitar Dimitrov wrote:
> A recent patch [1] to fix a GCC PR [2] actually broke the GDB build.
> To fix, remove the stack pointer clobber. GCC will ignore the clobber
> marker, and will not save or restore the stack pointer.
>
> I ran "make check-gdb" on x86_64 to ensure there are no regressions.
>
> gdb/ChangeLog:
>
> 2018-12-17  Dimitar Dimitrov  <dimitar@dinux.eu>
>
> 	* nat/linux-ptrace.c (linux_ptrace_test_ret_to_nx): Remove sp 
> clobbers.
>
> [1] https://gcc.gnu.org/ml/gcc-patches/2018-12/msg00532.html
> [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52813
>
> Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>
> ---
>  gdb/nat/linux-ptrace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/nat/linux-ptrace.c b/gdb/nat/linux-ptrace.c
> index 1f21ef03a3..58aed199bf 100644
> --- a/gdb/nat/linux-ptrace.c
> +++ b/gdb/nat/linux-ptrace.c
> @@ -128,14 +128,14 @@ linux_ptrace_test_ret_to_nx (void)
>  			".globl linux_ptrace_test_ret_to_nx_instr;"
>  			"linux_ptrace_test_ret_to_nx_instr:"
>  			"ret"
> -			: : "r" (return_address) : "%esp", "memory");
> +			: : "r" (return_address) : "memory");
>  #elif defined __x86_64__
>  	  asm volatile ("pushq %0;"
>  			".globl linux_ptrace_test_ret_to_nx_instr;"
>  			"linux_ptrace_test_ret_to_nx_instr:"
>  			"ret"
>  			: : "r" ((uint64_t) (uintptr_t) return_address)
> -			: "%rsp", "memory");
> +			: "memory");
>  #else
>  # error "!__i386__ && !__x86_64__"
>  #endif

LGTM:

1. We push a return address and ret, so in the end the stack point has 
not changed.
2. This is executed in a child process, which immediately stops on a 
breakpoint and never continues, even if the stack pointer was messed up, 
we wouldn't notice.

Do you have push access, or would you like me to push the patch for you?

Simon