Re: [PATCH] gcov-tool: Allow merging of empty profile lists

["Martin Liška" <mliska@suse.cz>]

On 3/28/22 18:23, Sebastian Huber wrote:
> On 24/03/2022 13:03, Martin Liška wrote:
>> On 3/24/22 11:51, Sebastian Huber wrote:
>>> Maybe we could add the file path into the gcov information stream using a new tag:
>>>
>>> #define GCOV_TAG_GCDA_FILE_NAME  ((gcov_unsigned_t)0xa5000000)
>>>
>>> Then the complete gcov information can be dumped using a single base64 encoded stream. We could add some support to the gcov-tool to read this stream and merge it into gcda files.
>>
>> I would support such patch!
> 
> Ok, good. I work currently on a prototype implementation. My use case would be like this.
> 

Great, the suggested scheme works for me.

> Run a test executable which dumps all gcov info objects in a serial data stream. It could be encoded as base64. It could be also compressed. On the host you unpack the encoded data stream and feed it into gcov-tool using the new "merge-stream" subcommand:
> 
> gcov-tool --help
> Usage: gcov-tool [OPTION]... SUB_COMMAND [OPTION]...
> 
> Offline tool to handle gcda counts
> 
>    -h, --help                            Print this help, then exit
>    -v, --version                         Print version number, then exit
>    merge-stream [options] [stream-file]  Merge coverage stream file (or stdin)
>                                          and coverage file contents
>      -v, --verbose                       Verbose mode
>      -w, --weight <w1,w2>                Set weights (float point values)
> 
> Example:
> 
> base64 -d log.txt | gcov-tool merge-stream
> 
> The gcov-tool uses a new tag which contains the filename of the associated gcov info file:
> 
> gcov-dump b-xilinx_zynq_a9_qemu/init.gcda
> b-xilinx_zynq_a9_qemu/init.gcda:data:magic `gcda':version `B20 '
> b-xilinx_zynq_a9_qemu/init.gcda:stamp 3496756572
> b-xilinx_zynq_a9_qemu/init.gcda:checksum 137326246
> b-xilinx_zynq_a9_qemu/init.gcda:  a5000000:  62:FILENAME `/home/EB/sebastian_h/src/lwip/b-xilinx_zynq_a9_qemu/init.gcda'
> b-xilinx_zynq_a9_qemu/init.gcda:  a1000000:   8:OBJECT_SUMMARY runs=0, sum_max=0
> b-xilinx_zynq_a9_qemu/init.gcda:  01000000:  12:FUNCTION ident=1016818396, lineno_checksum=0xd31791e7, cfg_checksum=0x4529789a
> b-xilinx_zynq_a9_qemu/init.gcda:    01a10000: 232:COUNTERS arcs 29 counts
> 
> Should I generate this filename tag to all configurations or just in case inhibit_libc is defined?

I would emit it unconditionally. Btw. why do you need the tag?

Cheers,
Martin

> 
> Advantage:
> 
> * No dependency on the GCC configuration
> 
> Disadvantages:
> 
> * Bigger files
> * Actual filename and the filename of the tag differ if file is moved
> * Potential information leak
> 
> In any case, I would add the support for the (optional) filename tag to all readers.
>