[PATCH bpf-next] tools/bpftool: turn off -Wnested-externs warning

[PATCH bpf-next] tools/bpftool: turn off -Wnested-externs warning

[Andrii Nakryiko]

Turn off -Wnested-externs to avoid annoying warnings in BUILD_BUG_ON macro when
compiling bpftool:

In file included from /data/users/andriin/linux/tools/include/linux/build_bug.h:5,
                 from /data/users/andriin/linux/tools/include/linux/kernel.h:8,
                 from /data/users/andriin/linux/kernel/bpf/disasm.h:10,
                 from /data/users/andriin/linux/kernel/bpf/disasm.c:8:
/data/users/andriin/linux/kernel/bpf/disasm.c: In function ‘__func_get_name’:
/data/users/andriin/linux/tools/include/linux/compiler.h:37:38: warning: nested extern declaration of ‘__compiletime_assert_0’ [-Wnested-externs]
  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
                                      ^~~~~~~~~~~~~~~~~~~~~
/data/users/andriin/linux/tools/include/linux/compiler.h:16:15: note: in definition of macro ‘__compiletime_assert’
   extern void prefix ## suffix(void) __compiletime_error(msg); \
               ^~~~~~
/data/users/andriin/linux/tools/include/linux/compiler.h:37:2: note: in expansion of macro ‘_compiletime_assert’
  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
  ^~~~~~~~~~~~~~~~~~~
/data/users/andriin/linux/tools/include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
/data/users/andriin/linux/tools/include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
  ^~~~~~~~~~~~~~~~
/data/users/andriin/linux/kernel/bpf/disasm.c:20:2: note: in expansion of macro ‘BUILD_BUG_ON’
  BUILD_BUG_ON(ARRAY_SIZE(func_id_str) != __BPF_FUNC_MAX_ID);
  ^~~~~~~~~~~~

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/bpf/bpftool/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index 273da1615503..51bd520ed437 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -40,7 +40,7 @@ bash_compdir ?= /usr/share/bash-completion/completions
 
 CFLAGS += -O2
 CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers
-CFLAGS += $(filter-out -Wswitch-enum,$(EXTRA_WARNINGS))
+CFLAGS += $(filter-out -Wswitch-enum -Wnested-externs,$(EXTRA_WARNINGS))
 CFLAGS += -DPACKAGE='"bpftool"' -D__EXPORTED_HEADERS__ \
 	-I$(if $(OUTPUT),$(OUTPUT),.) \
 	-I$(srctree)/kernel/bpf/ \
-- 
2.24.1

Re: [PATCH bpf-next] tools/bpftool: turn off -Wnested-externs warning

[Daniel Borkmann]

On 7/1/20 11:28 PM, Andrii Nakryiko wrote:
> Turn off -Wnested-externs to avoid annoying warnings in BUILD_BUG_ON macro when
> compiling bpftool:
> 
> In file included from /data/users/andriin/linux/tools/include/linux/build_bug.h:5,
>                   from /data/users/andriin/linux/tools/include/linux/kernel.h:8,
>                   from /data/users/andriin/linux/kernel/bpf/disasm.h:10,
>                   from /data/users/andriin/linux/kernel/bpf/disasm.c:8:
> /data/users/andriin/linux/kernel/bpf/disasm.c: In function ‘__func_get_name’:
> /data/users/andriin/linux/tools/include/linux/compiler.h:37:38: warning: nested extern declaration of ‘__compiletime_assert_0’ [-Wnested-externs]
>    _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>                                        ^~~~~~~~~~~~~~~~~~~~~
> /data/users/andriin/linux/tools/include/linux/compiler.h:16:15: note: in definition of macro ‘__compiletime_assert’
>     extern void prefix ## suffix(void) __compiletime_error(msg); \
>                 ^~~~~~
> /data/users/andriin/linux/tools/include/linux/compiler.h:37:2: note: in expansion of macro ‘_compiletime_assert’
>    _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>    ^~~~~~~~~~~~~~~~~~~
> /data/users/andriin/linux/tools/include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
>   #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                       ^~~~~~~~~~~~~~~~~~
> /data/users/andriin/linux/tools/include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
>    BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>    ^~~~~~~~~~~~~~~~
> /data/users/andriin/linux/kernel/bpf/disasm.c:20:2: note: in expansion of macro ‘BUILD_BUG_ON’
>    BUILD_BUG_ON(ARRAY_SIZE(func_id_str) != __BPF_FUNC_MAX_ID);
>    ^~~~~~~~~~~~
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Lgtm, thanks for fixing, applied!