[PATCH] bpf: use -Wno-error in certain tests when building with GCC

[PATCH] bpf: use -Wno-error in certain tests when building with GCC

[Jose E. Marchesi]

Certain BPF selftests contain code that, albeit being legal C, trigger
warnings in GCC that cannot be disabled.  This is the case for example
for the tests

  progs/btf_dump_test_case_bitfields.c
  progs/btf_dump_test_case_namespacing.c
  progs/btf_dump_test_case_packing.c
  progs/btf_dump_test_case_padding.c
  progs/btf_dump_test_case_syntax.c

which contain struct type declarations inside function parameter
lists.  This is problematic, because:

- The BPF selftests are built with -Werror.

- The Clang and GCC compilers sometimes differ when it comes to handle
  warnings.  in the handling of warnings.  One compiler may emit
  warnings for code that the other compiles compiles silently, and one
  compiler may offer the possibility to disable certain warnings, while
  the other doesn't.

In order to overcome this problem, this patch modifies the
tools/testing/selftests/bpf/Makefile in order to:

1. Enable the possibility of specifing per-source-file extra CFLAGS.
   This is done by defining a make variable like:

   <source-filename>-CFLAGS := <whateverflags>

   And then modifying the proper Make rule in order to use these flags
   when compiling <source-filename>.

2. Use the mechanism above to add -Wno-error to CFLAGS for the
   following selftests:

   progs/btf_dump_test_case_bitfields.c
   progs/btf_dump_test_case_namespacing.c
   progs/btf_dump_test_case_packing.c
   progs/btf_dump_test_case_padding.c
   progs/btf_dump_test_case_syntax.c

   Note the corresponding -CFLAGS variables for these files are
   defined only if the selftests are being built with GCC.

Note that, while compiler pragmas can generally be used to disable
particular warnings per file, this 1) is only possible for warning
that actually can be disabled in the command line, i.e. that have
-Wno-FOO options, and 2) doesn't apply to -Wno-error.

Tested in bpf-next master branch.
No regressions.

Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
Cc: Yonghong Song <yhs@meta.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: david.faust@oracle.com
Cc: cupertino.miranda@oracle.com
---
 tools/testing/selftests/bpf/Makefile | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index fd15017ed3b1..8c4282766976 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -64,6 +64,15 @@ TEST_INST_SUBDIRS := no_alu32
 ifneq ($(BPF_GCC),)
 TEST_GEN_PROGS += test_progs-bpf_gcc
 TEST_INST_SUBDIRS += bpf_gcc
+
+# The following tests contain C code that, although technically legal,
+# triggers GCC warnings that cannot be disabled: declaration of
+# anonymous struct types in function parameter lists.
+progs/btf_dump_test_case_bitfields.c-CFLAGS := -Wno-error
+progs/btf_dump_test_case_namespacing.c-CFLAGS := -Wno-error
+progs/btf_dump_test_case_packing.c-CFLAGS := -Wno-error
+progs/btf_dump_test_case_padding.c-CFLAGS := -Wno-error
+progs/btf_dump_test_case_syntax.c-CFLAGS := -Wno-error
 endif
 
 ifneq ($(CLANG_CPUV4),)
@@ -504,7 +513,8 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.bpf.o:				\
 		     $(wildcard $(BPFDIR)/*.bpf.h)			\
 		     | $(TRUNNER_OUTPUT) $$(BPFOBJ)
 	$$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,			\
-					  $(TRUNNER_BPF_CFLAGS))
+					  $(TRUNNER_BPF_CFLAGS)         \
+					  $$(if $$($$<-CFLAGS),$$($$<-CFLAGS)))
 
 $(TRUNNER_BPF_SKELS): %.skel.h: %.bpf.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
 	$$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
-- 
2.30.2

Re: [PATCH] bpf: use -Wno-error in certain tests when building with GCC

[Andrii Nakryiko]

On Fri, Jan 26, 2024 at 10:51 AM Jose E. Marchesi
<jose.marchesi@oracle.com> wrote:
>
> Certain BPF selftests contain code that, albeit being legal C, trigger
> warnings in GCC that cannot be disabled.  This is the case for example
> for the tests
>
>   progs/btf_dump_test_case_bitfields.c
>   progs/btf_dump_test_case_namespacing.c
>   progs/btf_dump_test_case_packing.c
>   progs/btf_dump_test_case_padding.c
>   progs/btf_dump_test_case_syntax.c
>
> which contain struct type declarations inside function parameter
> lists.  This is problematic, because:
>
> - The BPF selftests are built with -Werror.
>
> - The Clang and GCC compilers sometimes differ when it comes to handle
>   warnings.  in the handling of warnings.  One compiler may emit
>   warnings for code that the other compiles compiles silently, and one
>   compiler may offer the possibility to disable certain warnings, while
>   the other doesn't.
>
> In order to overcome this problem, this patch modifies the
> tools/testing/selftests/bpf/Makefile in order to:
>
> 1. Enable the possibility of specifing per-source-file extra CFLAGS.
>    This is done by defining a make variable like:
>
>    <source-filename>-CFLAGS := <whateverflags>
>
>    And then modifying the proper Make rule in order to use these flags
>    when compiling <source-filename>.
>
> 2. Use the mechanism above to add -Wno-error to CFLAGS for the
>    following selftests:
>
>    progs/btf_dump_test_case_bitfields.c
>    progs/btf_dump_test_case_namespacing.c
>    progs/btf_dump_test_case_packing.c
>    progs/btf_dump_test_case_padding.c
>    progs/btf_dump_test_case_syntax.c
>
>    Note the corresponding -CFLAGS variables for these files are
>    defined only if the selftests are being built with GCC.
>
> Note that, while compiler pragmas can generally be used to disable
> particular warnings per file, this 1) is only possible for warning
> that actually can be disabled in the command line, i.e. that have
> -Wno-FOO options, and 2) doesn't apply to -Wno-error.
>
> Tested in bpf-next master branch.
> No regressions.
>
> Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
> Cc: Yonghong Song <yhs@meta.com>
> Cc: Eduard Zingerman <eddyz87@gmail.com>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Cc: david.faust@oracle.com
> Cc: cupertino.miranda@oracle.com
> ---
>  tools/testing/selftests/bpf/Makefile | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index fd15017ed3b1..8c4282766976 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -64,6 +64,15 @@ TEST_INST_SUBDIRS := no_alu32
>  ifneq ($(BPF_GCC),)
>  TEST_GEN_PROGS += test_progs-bpf_gcc
>  TEST_INST_SUBDIRS += bpf_gcc
> +
> +# The following tests contain C code that, although technically legal,
> +# triggers GCC warnings that cannot be disabled: declaration of
> +# anonymous struct types in function parameter lists.
> +progs/btf_dump_test_case_bitfields.c-CFLAGS := -Wno-error
> +progs/btf_dump_test_case_namespacing.c-CFLAGS := -Wno-error
> +progs/btf_dump_test_case_packing.c-CFLAGS := -Wno-error
> +progs/btf_dump_test_case_padding.c-CFLAGS := -Wno-error
> +progs/btf_dump_test_case_syntax.c-CFLAGS := -Wno-error
>  endif
>
>  ifneq ($(CLANG_CPUV4),)
> @@ -504,7 +513,8 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.bpf.o:                             \
>                      $(wildcard $(BPFDIR)/*.bpf.h)                      \
>                      | $(TRUNNER_OUTPUT) $$(BPFOBJ)
>         $$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,                      \
> -                                         $(TRUNNER_BPF_CFLAGS))
> +                                         $(TRUNNER_BPF_CFLAGS)         \
> +                                         $$(if $$($$<-CFLAGS),$$($$<-CFLAGS)))

minor nit, but do you even need the $$(if)? why not just
unconditionally use $$($$<-CFLAGS) which should result in an empty
string, right? Or is there some make weirdness that I'm forgetting?

>
>  $(TRUNNER_BPF_SKELS): %.skel.h: %.bpf.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
>         $$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
> --
> 2.30.2
>

Re: [PATCH] bpf: use -Wno-error in certain tests when building with GCC

[Jose E. Marchesi]

> On Fri, Jan 26, 2024 at 10:51 AM Jose E. Marchesi
> <jose.marchesi@oracle.com> wrote:
>>
>> Certain BPF selftests contain code that, albeit being legal C, trigger
>> warnings in GCC that cannot be disabled.  This is the case for example
>> for the tests
>>
>>   progs/btf_dump_test_case_bitfields.c
>>   progs/btf_dump_test_case_namespacing.c
>>   progs/btf_dump_test_case_packing.c
>>   progs/btf_dump_test_case_padding.c
>>   progs/btf_dump_test_case_syntax.c
>>
>> which contain struct type declarations inside function parameter
>> lists.  This is problematic, because:
>>
>> - The BPF selftests are built with -Werror.
>>
>> - The Clang and GCC compilers sometimes differ when it comes to handle
>>   warnings.  in the handling of warnings.  One compiler may emit
>>   warnings for code that the other compiles compiles silently, and one
>>   compiler may offer the possibility to disable certain warnings, while
>>   the other doesn't.
>>
>> In order to overcome this problem, this patch modifies the
>> tools/testing/selftests/bpf/Makefile in order to:
>>
>> 1. Enable the possibility of specifing per-source-file extra CFLAGS.
>>    This is done by defining a make variable like:
>>
>>    <source-filename>-CFLAGS := <whateverflags>
>>
>>    And then modifying the proper Make rule in order to use these flags
>>    when compiling <source-filename>.
>>
>> 2. Use the mechanism above to add -Wno-error to CFLAGS for the
>>    following selftests:
>>
>>    progs/btf_dump_test_case_bitfields.c
>>    progs/btf_dump_test_case_namespacing.c
>>    progs/btf_dump_test_case_packing.c
>>    progs/btf_dump_test_case_padding.c
>>    progs/btf_dump_test_case_syntax.c
>>
>>    Note the corresponding -CFLAGS variables for these files are
>>    defined only if the selftests are being built with GCC.
>>
>> Note that, while compiler pragmas can generally be used to disable
>> particular warnings per file, this 1) is only possible for warning
>> that actually can be disabled in the command line, i.e. that have
>> -Wno-FOO options, and 2) doesn't apply to -Wno-error.
>>
>> Tested in bpf-next master branch.
>> No regressions.
>>
>> Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
>> Cc: Yonghong Song <yhs@meta.com>
>> Cc: Eduard Zingerman <eddyz87@gmail.com>
>> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
>> Cc: david.faust@oracle.com
>> Cc: cupertino.miranda@oracle.com
>> ---
>>  tools/testing/selftests/bpf/Makefile | 12 +++++++++++-
>>  1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index fd15017ed3b1..8c4282766976 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -64,6 +64,15 @@ TEST_INST_SUBDIRS := no_alu32
>>  ifneq ($(BPF_GCC),)
>>  TEST_GEN_PROGS += test_progs-bpf_gcc
>>  TEST_INST_SUBDIRS += bpf_gcc
>> +
>> +# The following tests contain C code that, although technically legal,
>> +# triggers GCC warnings that cannot be disabled: declaration of
>> +# anonymous struct types in function parameter lists.
>> +progs/btf_dump_test_case_bitfields.c-CFLAGS := -Wno-error
>> +progs/btf_dump_test_case_namespacing.c-CFLAGS := -Wno-error
>> +progs/btf_dump_test_case_packing.c-CFLAGS := -Wno-error
>> +progs/btf_dump_test_case_padding.c-CFLAGS := -Wno-error
>> +progs/btf_dump_test_case_syntax.c-CFLAGS := -Wno-error
>>  endif
>>
>>  ifneq ($(CLANG_CPUV4),)
>> @@ -504,7 +513,8 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.bpf.o:                             \
>>                      $(wildcard $(BPFDIR)/*.bpf.h)                      \
>>                      | $(TRUNNER_OUTPUT) $$(BPFOBJ)
>>         $$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,                      \
>> -                                         $(TRUNNER_BPF_CFLAGS))
>> +                                         $(TRUNNER_BPF_CFLAGS)         \
>> +                                         $$(if $$($$<-CFLAGS),$$($$<-CFLAGS)))
>
> minor nit, but do you even need the $$(if)? why not just
> unconditionally use $$($$<-CFLAGS) which should result in an empty
> string, right? Or is there some make weirdness that I'm forgetting?

Indeed.  Good catch.  The $(if ...) was a vestigious of some testing.
Just sent V2.

>>
>>  $(TRUNNER_BPF_SKELS): %.skel.h: %.bpf.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
>>         $$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
>> --
>> 2.30.2
>>