Re: [Minios-devel] [UNIKRAFT PATCH 4/8] lib/ukdebug: key-value static storage for tracing

[Costin Lupu <costin.lup@xxxxxxxxx>]

And another thing I forgot, please see inline.

On 5/29/19 8:27 AM, Costin Lupu wrote:
> Hi Yuri,
> 
> It's not obvious why we need this key-value thing. Can you please extend
> the commit message or the comment or both with some use cases where this
> would be useful?
> 
> Thanks,
> Costin
> 
> On 5/10/19 9:29 PM, Yuri Volchkov wrote:
>> One more 'special' stripable section. Will contain strings in format
>> key = value. Currently only tracebuffer format version is stored there.
>>
>> Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
>> ---
>>  lib/ukdebug/extra.ld |  3 +++
>>  lib/ukdebug/trace.c  | 18 ++++++++++++++++++
>>  2 files changed, 21 insertions(+)
>>
>> diff --git a/lib/ukdebug/extra.ld b/lib/ukdebug/extra.ld
>> index 43154f9d..bb0b36b8 100644
>> --- a/lib/ukdebug/extra.ld
>> +++ b/lib/ukdebug/extra.ld
>> @@ -5,6 +5,9 @@ SECTIONS
>>              KEEP (*(.uk_tracepoints_list));
>>              uk_tracepoints_end = .;
>>      }
>> +    .uk_trace_keyvals : {
>> +            KEEP (*(.uk_trace_keyvals));
>> +    }
>>  }
>>  
>>  /* We do not want these section to be in the final image, they are
>> diff --git a/lib/ukdebug/trace.c b/lib/ukdebug/trace.c
>> index f3318557..91cc2387 100644
>> --- a/lib/ukdebug/trace.c
>> +++ b/lib/ukdebug/trace.c
>> @@ -43,3 +43,21 @@ char uk_trace_buffer[UK_TRACE_BUFFER_SIZE];
>>  
>>  size_t uk_trace_buffer_free = UK_TRACE_BUFFER_SIZE;
>>  char *uk_trace_buffer_writep = uk_trace_buffer;
>> +
>> +
>> +/* Store a string in format "key = value" in the section
>> + * .uk_trace_keyvals. This can be anything what you want trace.py
>> + * script to know about, and what you do not want to consume any space
>> + * in runtime memory.
>> + *
>> + * This section will be stripped at the final states of building, but
>> + * the key-value data can be easily extracted by:
>> + *
>> + *     $ readelf -p .uk_trace_keyvals <your_image.gdb>

In my case it's not in 'image.gdb', it's in 'image'. Maybe because
'build: always produce 2 images: w/ and w/o debug syms' wasn't upstreamed?

>> + */
>> +#define TRACE_DEFINE_KEY(key, val)                  \
>> +    __attribute((__section__(".uk_trace_keyvals"))) \
>> +    static const char key[] __used =                \
>> +            #key " = " #val
>> +
>> +TRACE_DEFINE_KEY(format_version, 1);
>>
> 
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