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

[Costin Lupu <costin.lup@xxxxxxxxx>]

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>
> + */
> +#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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