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

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

On 30/03/2022 15:30, Sebastian Huber wrote:
> On 30/03/2022 13:56, Martin Liška wrote:
>>> 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?
> 
> The tag was the easiest way to add the filename to the gcov information.
> 
> We need some gcov defined way to get the filename associated with a gcov 
> information, so that the gcov-tool can generate the gcov files from the 
> gcov information itself. In a hosted environment, it is not necessary to 
> include the filename in the gcov information, since the instrumented 
> executable already creates the gcov files. In a freestanding 
> environment, the gcov information is not automatically stored to files 
> since no file system may be available. Here, we can dump the gcov 
> information through __gcov_info_to_gcda(). This dump is basically a 
> concatenation of several gcov files.
> 
> An alternative to a tag inside the gcov data would be a header which is 
> dumped before the gcov data and understood by the gcov-tool:
> 
> header : int32:filename-magic int32:version string
> 
> #define GCOV_FILENAME_MAGIC ((gcov_unsigned_t)0x6763666e) /* "gcfn" */

Thanks for asking the question. The alternative with the header is much 
less intrusive. I will work on this approach now.

Another question, I would like to add an option to gcov-tool to 
transform the filenames using regular expressions (for example, remove 
or add a prefix). Can I use the C++ <regex> for this?

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