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btrfs-progs: kerncompat: fix fallthrough definition for gcc 5.x and 6.x. 

Commit [1] 3a1d4aa089 "btrfs-progs: fix fallthrough cases with proper
attributes" introduced a macro "fallthrough" to better handle compiler
warnings of fallthrough situations.

This macro is defined using the "__has_attribute" built-in
function-like macro, which was introduced in GCC 5. See [2]. It then
test for the "__fallthrough__" attribute, which was introduced in
GCC 7. See [3].

When compiling with a gcc version which supports "__has_attribute" and
not the "__fallthrough__" attribute, compilation fails with error
message:

    common/format-output.c: In function 'print_escaped':
    common/format-output.c:78:4: error: 'fallthrough' undeclared (first use in this function)
        fallthrough;
        ^
btrfs-progs claim to support gcc at minimal version 4.8 in [4].

This commit fixes this issue by adding the missing definition.

The definition of the unsupported case is duplicated, because testing
for "__has_attribute" and an attribute at the same time is not
portable. See the cpp "__has_attribute" documentation [5].

Note: the issue was found with Buildroot Linux [6], while testing with
the command "utils/test-pkg -a -p btrfs-progs".

[1] 3a1d4aa089
[2] https://gcc.gnu.org/gcc-5/changes.html
[3] https://gcc.gnu.org/gcc-7/changes.html
[4] https://github.com/kdave/btrfs-progs/tree/v6.9.2#build-compatibility
[5] https://gcc.gnu.org/onlinedocs/cpp/_005f_005fhas_005fattribute.html
[6] https://buildroot.org/

Pull-request: #842
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Julien Olivain 2024-07-14 12:52:33 +02:00 committed by David Sterba
parent 2c697677e7
commit e1c5238ba2
1 changed files with 3 additions and 0 deletions
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3
include/kerncompat.h
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@ -305,6 +305,9 @@ static inline void up_read(struct rw_semaphore *sem)
#if defined __has_attribute
# if __has_attribute(__fallthrough__)
# define fallthrough __attribute__((__fallthrough__))
# else
/* Compatibility with gcc 5.x and 6.x that don't have the attribute. */
# define fallthrough do {} while (0) /* fallthrough */
# endif
#else
# define fallthrough do {} while (0) /* fallthrough */