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Re: [PATCH 1/2] Fix PR gdb/19676: Disable displaced stepping if /proc not mounted
- From: Simon Marchi <simon dot marchi at ericsson dot com>
- To: Pedro Alves <palves at redhat dot com>, <gdb-patches at sourceware dot org>
- Date: Tue, 1 Mar 2016 12:00:42 -0500
- Subject: Re: [PATCH 1/2] Fix PR gdb/19676: Disable displaced stepping if /proc not mounted
- Authentication-results: sourceware.org; auth=none
- References: <1456850713-5745-1-git-send-email-palves at redhat dot com> <1456850713-5745-2-git-send-email-palves at redhat dot com>
On 16-03-01 11:45 AM, Pedro Alves wrote:
> On GNU/Linux archs that support displaced stepping, if /proc is not
> mounted, GDB gets stuck not able to step past breakpoints:
>
> (gdb) c
> Continuing.
> dl_main (phdr=<optimized out>, phnum=<optimized out>, user_entry=<optimized out>, auxv=<optimized out>) at rtld.c:2163
> 2163 LIBC_PROBE (init_complete, 2, LM_ID_BASE, r);
> Cannot find AT_ENTRY auxiliary vector entry.
> (gdb) c
> Continuing.
> dl_main (phdr=<optimized out>, phnum=<optimized out>, user_entry=<optimized out>, auxv=<optimized out>) at rtld.c:2163
> 2163 LIBC_PROBE (init_complete, 2, LM_ID_BASE, r);
> Cannot find AT_ENTRY auxiliary vector entry.
> (gdb)
>
> That's because GDB can't figure out where the scratch pad is.
>
> This is a regression introduced by the earlier changes to make the
> Linux native target always work in non-stop mode.
>
> This commit makes GDB detect the case and fallback to stepping over
> breakpoints in-line.
>
> gdb/ChangeLog:
> 2016-03-01 Pedro Alves <pedro@cascais.lan>
>
> PR gdb/19676
> * infrun.c (displaced_step_prepare): Also disable displaced
> stepping on NOT_SUPPORTED_ERROR.
> * linux-tdep.c (linux_displaced_step_location): If reading auxv
> fails, throw NOT_SUPPORTED_ERROR instead of generic error.
> ---
> gdb/infrun.c | 3 ++-
> gdb/linux-tdep.c | 3 ++-
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 3e8c9e0..696105d 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -1894,7 +1894,8 @@ displaced_step_prepare (ptid_t ptid)
> {
> struct displaced_step_inferior_state *displaced_state;
>
> - if (ex.error != MEMORY_ERROR)
> + if (ex.error != MEMORY_ERROR
> + && ex.error != NOT_SUPPORTED_ERROR)
> throw_exception (ex);
>
> if (debug_infrun)
> diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
> index 555c302..f197aa7 100644
> --- a/gdb/linux-tdep.c
> +++ b/gdb/linux-tdep.c
> @@ -2426,7 +2426,8 @@ linux_displaced_step_location (struct gdbarch *gdbarch)
> location. The auxiliary vector gets us the PowerPC-side entry
> point address instead. */
> if (target_auxv_search (¤t_target, AT_ENTRY, &addr) <= 0)
> - error (_("Cannot find AT_ENTRY auxiliary vector entry."));
> + throw_error (NOT_SUPPORTED_ERROR,
> + _("Cannot find AT_ENTRY auxiliary vector entry."));
>
> /* Make certain that the address points at real code, and not a
> function descriptor. */
>
Whoa, I didn't even know you could run without proc.
You would probably have seen it anyway, but the email address in your
ChangeLog entries has a local host name.
Simon