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

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

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.

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?

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.

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