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

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

On 12/26/20 7:23 PM, Simon Marchi wrote:
> 
> 
> On 2020-11-09 12:04 p.m., Luis Machado via Gdb-patches 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.
> 
> Can you give an example of the end result message?
> 

I've attached it to the commit message.

The synchronous event looks like this:

--
(gdb) continue
Continuing.

Program received signal SIGSEGV, Segmentation fault
Memory tag violation while accessing address 0x0000fffff7ff8000
Allocation tag 0x1.
--

The asynchronous event looks like this:

--
(gdb) continue
Continuing.

Program received signal SIGSEGV, Segmentation fault
Memory tag violation
Fault address unavailable.
--

>>
>> 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");
> 
> Is the \n necessary?
> 

No. Fixed now.

>> +
>> +      fault_addr
>> +	= parse_and_eval_long ("$_siginfo._sifields._sigfault.si_addr");
>> +    }
>> +  catch (const gdb_exception &exception)
>> +    {
>> +      return;
>> +    }
> 
> I think it's better to catch gdb_exception_error, to avoid catching ^C
> (gdb_exception_quit).
> 
> And if there's an error doing the evaluation... do we want to print
> a warning of some sort?
> 

I went with printing the exception with...

exception_print (gdb_stderr, exception);


> Simon
>