[OE-core] [PATCH] perf: workaround the error cased by maybe-uninitialized warning

[Randy MacLeod]

On 4/5/19 5:55 PM, Khem Raj wrote:
> On Thu, Apr 4, 2019 at 2:03 AM Dengke Du <dengke.du at windriver.com> wrote:
>>
>> When enable DEBUG_BUILD, the perf build failed by the following error:
>>      libbpf.c:727:36: error: 'data' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>> This is ok until Khem commit a patch in oe-core:
>>      16643b03227466e2c80a24c2d079fe36e89553c1
>> This commit import "-Og" option to "DEBUG_OPTIMIZATION", result in this error.
>>
>> Actually, the warning was misinformation. We explore the code in libbpf.c:
>>      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/bpf/libbpf.c#n640
>> --------------------------------------------------------------------------
>>          if (scn)
>>                  data = elf_getdata(scn, NULL);
>>          if (!scn || !data) {
>>                  pr_warning("failed to get Elf_Data from map section %d\n",
>>                             obj->efile.maps_shndx);
>>                  return -EINVAL;
>>          }
>>          ......
>>          using data...
>>          ......
>> --------------------------------------------------------------------------
>> If the 'scn' was not null, the data will be initialized. if the data was null,
>> the function will return -EINVAL, so the data must be not null, but compiler
>> can't see it in 'if' code block, so treat it as 'maybe-uninitialized'.
>>
>> Signed-off-by: Dengke Du <dengke.du at windriver.com>
>> ---
>>   meta/recipes-kernel/perf/perf.bb | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/meta/recipes-kernel/perf/perf.bb b/meta/recipes-kernel/perf/perf.bb
>> index 5acdcfb..546076f 100644
>> --- a/meta/recipes-kernel/perf/perf.bb
>> +++ b/meta/recipes-kernel/perf/perf.bb
>> @@ -271,3 +271,4 @@ FILES_${PN}-perl = "${libexecdir}/perf-core/scripts/perl"
>>
>>
>>   INHIBIT_PACKAGE_DEBUG_SPLIT="1"
>> +DEBUG_OPTIMIZATION_append = " -Wno-error=maybe-uninitialized"
> 
> I was thinking that this would be applied globally, but I think doing
> it on need bases is a better approach so this looks ok to me.

so this commit should be merged.

I don't see it in master[-next] yet so this is a reminder to the busy,
hard-working gatekeepers. :)

../Randy
> 


-- 
# Randy MacLeod
# Wind River Linux