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

[Luis Machado via Gdb-patches <gdb-patches@sourceware.org>]

On 11/16/20 12:43 PM, David Spickett wrote:
>> +aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>> +                                 struct ui_out *uiout,
>> +                                 enum gdb_signal siggnal)
> 
> siggnal -> signal
> 

This is a GDB-ism. The hook itself is named like that. I don't like the 
name, but I thought I'd leave it the same just to keep it standard.

> 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.

We could print it without leading zeroes. That may make things a bit 
more compact. Would that work?

> 
> 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
>>