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SubjectRe: [PATCH] linux/fs.h - Convert debug functions declared inline __attribute__((format (printf,x,y) to statement expression macros
On Tue, 26 Feb 2008, Joe Perches wrote:

> > Joe, what version of gcc are you using?
>
> $ gcc --version
> gcc (GCC) 4.2.2 20071128 (prerelease) (4.2.2-3.1mdv2008.0)
>
> It's definitely odd.
> The .o size changes are inconsistent.
> Some get bigger, some get smaller.
>
> The versioning ones I understand but I have no idea why
> changes in drivers/ or mm/ or net/ exist.
>

When I did the same comparisons on my x86_64 defconfig with gcc 4.1.3, I
only saw differences in drivers/ and fs/.

> I think it's gcc optimization changes, but dunno...
> Any good ideas?
>

What's interesting about this is that it doesn't appear to be related to
your change (static inline function to macro definition). It appears to
be simply removing the static inline function.

The only reference to __simple_attr_check_format() in either the x86 or
x86_64 defconfig is via DEFINE_SIMPLE_ATTRIBUTE() in fs/debugfs/file.c.

If you remove the only reference to it:

diff --git a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2044,7 +2044,6 @@ static inline void simple_transaction_set(struct file *file, size_t n)
#define DEFINE_SIMPLE_ATTRIBUTE(__fops, __get, __set, __fmt) \
static int __fops ## _open(struct inode *inode, struct file *file) \
{ \
- __simple_attr_check_format(__fmt, 0ull); \
return simple_attr_open(inode, file, __get, __set, __fmt); \
} \
static struct file_operations __fops = { \
The text size remains the same:

text data bss dec hex filename
5386111 846328 719560 6951999 6a143f vmlinux.before
5386111 846328 719560 6951999 6a143f vmlinux.after

Yet if you remove the reference _and_ the static inline function itself,
replacing it with nothing:

diff --git a/include/linux/fs.h b/include/linux/fs.h
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2044,7 +2044,6 @@ static inline void simple_transaction_set(struct file *file, size_t n)
#define DEFINE_SIMPLE_ATTRIBUTE(__fops, __get, __set, __fmt) \
static int __fops ## _open(struct inode *inode, struct file *file) \
{ \
- __simple_attr_check_format(__fmt, 0ull); \
return simple_attr_open(inode, file, __get, __set, __fmt); \
} \
static struct file_operations __fops = { \
@@ -2055,12 +2054,6 @@ static struct file_operations __fops = { \
.write = simple_attr_write, \
};

-static inline void __attribute__((format(printf, 1, 2)))
-__simple_attr_check_format(const char *fmt, ...)
-{
- /* don't do anything, just let the compiler check the arguments; */
-}
-
int simple_attr_open(struct inode *inode, struct file *file,
int (*get)(void *, u64 *), int (*set)(void *, u64),
const char *fmt);
The text size does become smaller:

text data bss dec hex filename
5386111 846328 719560 6951999 6a143f vmlinux.before
5386047 846328 719560 6951935 6a13ff vmlinux.after

gcc 4.0.3 maintains the same text size for both cases, while it appears
gcc 4.1.3 and your version, 4.2.2, have this different behavior.

David


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