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

[Dimitar Dimitrov <dimitar@dinux.eu>]

On понеделник, 17 декември 2018 г. 22:05:11 EET Simon Marchi wrote:
> 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?
I do not have push access for GDB. Please push it for me.

Please note that discussion on GCC mailing list is still ongoing. I still 
think that this GDB patch should be merged, though.

https://gcc.gnu.org/ml/gcc-patches/2018-12/msg01250.html
https://gcc.gnu.org/ml/gcc-patches/2018-12/msg01308.html

Thanks,
Dimitar