Re: [PATCH v1 09/10] gdb/linux-tdep: parse ProtectionKey in /proc/PID/smaps

[Matthieu Longo <matthieu.longo@arm.com>]

On 09/07/2026 07:42, Thiago Jung Bauermann wrote:
> Matthieu Longo <matthieu.longo@arm.com> writes:
> 
>> Memory Protection Keys provide a mechanism for enforcing page-based
>> protections without requiring modification of the page tables
>> when an application changes protection domains. [1]
>>
>> The "ProtectionKey" field may be present in /proc/PID/smaps x86_64
>> and AArch64 systems since Linux 4.9, when the kernel is built with
>> Memory Protection Keys support.
> 
> /me from a previous life would feel the need to point out that it may
> also be present on POWER systems. :)
> 

Added PowerPC to the list.

  The "ProtectionKey" field may be present in /proc/PID/smaps x86_64,
  PowerPC, and AArch64 systems since Linux 4.9, when the kernel is
  built with Memory Protection Keys support.

>> Add a new 'pkey' field to `struct smaps_data', and populate it when
>> the "ProtectionKey" field is present.
>>
>> This prepares for displaying the protection key in 'info proc mappings'.
>>
>> [1]: https://docs.kernel.org/core-api/protection-keys.html,
>>      https://lkml.iu.edu/1512.0/03058.html
> 
> I suggest linking to the commit that went upstream instead of the
> mailing list patch:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c1192f842841
> 

Fixed.

>> ---
>>  gdb/linux-tdep.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
>> index dbc69a5a7fc..d89c5ae8504 100644
>> --- a/gdb/linux-tdep.c
>> +++ b/gdb/linux-tdep.c
>> @@ -124,6 +124,7 @@ struct smaps_data
>>  
>>    ULONGEST rss;
>>    ULONGEST swap;
>> +  std::optional<int> pkey;
> 
> There's nothing in this patch series that uses the parsed pkey, so IMHO
> (other maintainers may disagree) it makes more sense if this patch is
> committed together with a patch that makes use of the field.
> 

Nothing uses it yet because it is still unclear how to expose it to the users.
I assume that "info proc mappings" is a good place to do it.

As a reminder those are the existing columns:
Start Addr         End Addr           Size               Offset             Perms File

Should we add a new column "Protection Key" or "PKey" between "Offset" and "Perms" ?
What do you think ?

>>  };
>>  
>>  /* Whether to take the /proc/PID/coredump_filter into account when
>> @@ -1553,6 +1554,7 @@ parse_smaps_data (const file_reader_t<char> &freader)
>>        int mapping_file_p;
>>        ULONGEST rss = -1;
>>        ULONGEST swap = -1;
>> +      int pkey = -1;
>>  
>>        memset (&v, 0, sizeof (v));
>>        struct mapping m = read_mapping (line);
>> @@ -1653,6 +1655,16 @@ parse_smaps_data (const file_reader_t<char> &freader)
>>  		  mapping_anon_p = 1;
>>  		}
>>  	    }
>> +
>> +	  if (streq (keyword, "ProtectionKey:"))
>> +	    {
>> +	      if (sscanf (line, "%*s%d", &pkey) != 1)
>> +		{
>> +		  warning (_("Error parsing %s's value in {s,}maps file '%s'"),
>> +			   keyword, freader.c_filepath ());
>> +		  break;
>> +		}
>> +	    }
>>  	}
>>        /* Save the smaps entry to the vector.  */
>>  	struct smaps_data map;
>> @@ -1672,6 +1684,7 @@ parse_smaps_data (const file_reader_t<char> &freader)
>>  	map.inode = m.inode;
>>  	map.rss = rss;
>>  	map.swap = swap;
>> +	map.pkey.emplace (pkey);
> 
> Shouldn't map.pkey be set only if pkey != -1?
> 

Agree. Fixed.

>>  
>>  	smaps.emplace_back (map);
>>      }
> 

Matthieu