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

Luis Machado via Gdb-patches
2020-11-16T16:46:08Z

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
>>