Re: [patch] sigaltstack fixes for hppa-linux

[Andrew Cagney <cagney@gnu.org>]

>>> well, only because the hppa sigtramp unwinder is slightly broken :-) for
>>> the sigtramp frame it current uses the sp stored in the sigcontext as
>>> the frame base. instead it should probably use the handler's stack.
> 
> 
> here's a fixed version. No frame.c modifications needed :)
> 
> one question related to this: i noticed that some of the tests are
> failing when:
> - a breakpoint is placed in the signal trampoline (e.g. "finish" from 
>   the signal handler)
> - we try to unwind from the signal trampoline frame
> 
> they fail because breakpoints are not yet disabled when the unwinding
> starts (get_frame_id() is called early on in handle_inferior_event, 
> which runs through the unwinders)
> 
> Are the unwinders that do code matching supposed to deal with the case
> where there are breakpoints inserted in the code stream? or does this
> point to something else that is broken?

Yes, use frame*memory* and it will work (see tramp-frame.c: 
tramp_frame_start()) (and yes, having those memory routines possibly 
include breakpoints is just weird).

Feel free to fix any other HP unwinders with a follow-on commit.

Some suggested tweaks before committing follow:

> 2004-05-06  Randolph Chung  <tausq@debian.org>
> 
> 	* hppa-linux-tdep.c (hppa_linux_sigtramp_find_sigcontext): Pass in pc
> 	instead of sp, handle sigaltstack case.
> 	(hppa_linux_sigtramp_frame_unwind_cache): Adjust calls to 
> 	hppa_linux_sigtramp_find_sigcontext, and set base to the frame of the
> 	signal handler and not that of the caller.
> 	(hppa_linux_sigtramp_unwind_sniffer): Adjust calls to
> 	hppa_linux_sigtramp_find_sigcontext.
> 
> Index: hppa-linux-tdep.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/hppa-linux-tdep.c,v
> retrieving revision 1.2
> diff -u -p -r1.2 hppa-linux-tdep.c
> --- hppa-linux-tdep.c	7 May 2004 05:48:49 -0000	1.2
> +++ hppa-linux-tdep.c	7 May 2004 06:24:07 -0000
> @@ -282,7 +284,7 @@ hppa_linux_skip_trampoline_code (CORE_AD
>     Note that with a 2.4 64-bit kernel, the signal context is not properly
>     passed back to userspace so the unwind will not work correctly.  */
>  static CORE_ADDR
> -hppa_linux_sigtramp_find_sigcontext (CORE_ADDR sp)
> +hppa_linux_sigtramp_find_sigcontext (CORE_ADDR pc)
>  {
>    unsigned int dummy[HPPA_MAX_INSN_PATTERN_LEN];
>    int offs = 0;
> @@ -291,6 +293,12 @@ hppa_linux_sigtramp_find_sigcontext (COR
>    static int pcoffs[] = { 0, 4*4, 5*4 };
>    /* offsets to the rt_sigframe structure */
>    static int sfoffs[] = { 4*4, 10*4, 10*4 };
> +  CORE_ADDR sp;
> +
> +  /* Most of the time, this will be correct.  The one case when this will
> +     fail is if the user defined an alternate stack, in which case the
> +     beginning of the stack will not be pc & 63.  */
> +  sp = (pc & ~63);

Use align_down() (I never trust C's sign extension rules).

Andrew