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

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

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" */

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