Re: [PATCH v3 16/24] AArch64: Report tag violation error information

[David Spickett via Gdb-patches <gdb-patches@sourceware.org>]

> +aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
> +                                 struct ui_out *uiout,
> +                                 enum gdb_signal siggnal)

siggnal -> signal

Also a nit about the formatting.

Copying from 20/24 of v3:
> +Memory tag violation while accessing address 0x0000fffff7ff8000
> +Allocation tag 0x0000000000000001.

(I'm guessing the code to print the "Allocation tag" line lives here
in some part)

Would it make more sense to either not align the tag value to
anything, or to align it to the size of the architecture's tag? Which
would be 4 bits in this case so the same either way.

On Mon, 9 Nov 2020 at 17:05, Luis Machado <luis.machado@linaro.org> wrote:
>
> Whenever a memory tag violation occurs, we get a SIGSEGV. Additional
> information can be obtained through the siginfo data structure.
>
> For AArch64 the Linux kernel may expose the fault address and tag
> information, if we have a synchronous event. Otherwise there is
> no fault address available.
>
> gdb/ChangeLog:
>
> YYYY-MM-DD  Luis Machado  <luis.machado@linaro.org>
>
>         * aarch64-linux-tdep.c
>         (aarch64_linux_report_signal_info): New function.
>         (aarch64_linux_init_abi): Register
>         aarch64_linux_report_signal_info as the report_signal_info hook.
>         * arch/aarch64-linux.h (SEGV_MTEAERR): Define.
>         (SEGV_MTESERR): Define.
> ---
>  gdb/aarch64-linux-tdep.c     | 64 ++++++++++++++++++++++++++++++++++++
>  gdb/arch/aarch64-mte-linux.h |  6 ++++
>  2 files changed, 70 insertions(+)
>
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index 39b1790263..70e180e1cb 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -1626,6 +1626,67 @@ aarch64_linux_memtag_to_string (struct gdbarch *gdbarch,
>    return string_printf ("0x%s", phex_nz (tag, sizeof (tag)));
>  }
>
> +/* AArch64 Linux implementation of the report_signal_info gdbarch
> +   hook.  Displays information about possible memory tag violations.  */
> +
> +static void
> +aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
> +                                 struct ui_out *uiout,
> +                                 enum gdb_signal siggnal)
> +{
> +  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
> +
> +  if (!tdep->has_mte () || siggnal != GDB_SIGNAL_SEGV)
> +    return;
> +
> +  CORE_ADDR fault_addr = 0;
> +  long si_code = 0;
> +
> +  try
> +    {
> +      /* Sigcode tells us if the segfault is actually a memory tag
> +        violation.  */
> +      si_code = parse_and_eval_long ("$_siginfo.si_code\n");
> +
> +      fault_addr
> +       = parse_and_eval_long ("$_siginfo._sifields._sigfault.si_addr");
> +    }
> +  catch (const gdb_exception &exception)
> +    {
> +      return;
> +    }
> +
> +  /* If this is not a memory tag violation, just return.  */
> +  if (si_code != SEGV_MTEAERR && si_code != SEGV_MTESERR)
> +    return;
> +
> +  uiout->text ("\n");
> +
> +  uiout->field_string ("sigcode-meaning", _("Memory tag violation"));
> +
> +  /* For synchronous faults, show additional information.  */
> +  if (si_code == SEGV_MTESERR)
> +    {
> +      uiout->text (_(" while accessing address "));
> +      uiout->field_core_addr ("fault-addr", gdbarch, fault_addr);
> +      uiout->text ("\n");
> +
> +      CORE_ADDR atag;
> +      if (aarch64_linux_get_atag (fault_addr, &atag) != 0)
> +       uiout->text (_("Allocation tag unavailable"));
> +      else
> +       {
> +         uiout->text (_("Allocation tag "));
> +         uiout->field_core_addr ("allocation-tag", gdbarch, atag);
> +       }
> +    }
> +  else
> +    {
> +      uiout->text ("\n");
> +      uiout->text (_("Fault address unavailable"));
> +    }
> +}
> +
>  static void
>  aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>  {
> @@ -1706,6 +1767,9 @@ aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>
>        /* Register a hook for converting a memory tag to a string.  */
>        set_gdbarch_memtag_to_string (gdbarch, aarch64_linux_memtag_to_string);
> +
> +      set_gdbarch_report_signal_info (gdbarch,
> +                                     aarch64_linux_report_signal_info);
>      }
>
>    /* Initialize the aarch64_linux_record_tdep.  */
> diff --git a/gdb/arch/aarch64-mte-linux.h b/gdb/arch/aarch64-mte-linux.h
> index 5c5783f28b..a5a980ed49 100644
> --- a/gdb/arch/aarch64-mte-linux.h
> +++ b/gdb/arch/aarch64-mte-linux.h
> @@ -35,6 +35,12 @@
>  #define MTE_LOGICAL_TAG_START_BIT   56
>  #define MTE_LOGICAL_MAX_VALUE      0xf
>
> +/* Memory tagging definitions.  */
> +#ifndef SEGV_MTEAERR
> +# define SEGV_MTEAERR 8
> +# define SEGV_MTESERR 9
> +#endif
> +
>  /* Return the number of tag granules in the memory range
>     [ADDR, ADDR + LEN) given GRANULE_SIZE.  */
>  extern size_t get_tag_granules (CORE_ADDR addr, size_t len,
> --
> 2.17.1
>