Re: [Qemu-devel] [PATCH] scripts/checkpatch.pl: fix false error ofexterns checking.

[jiang.biao2]

> On 10 October 2017 at 08:54, Jiang Biao <address@hidden> wrote:


> > When adding a function declaration in a .c file without extern
> >keywork decoration, checkpatch.pl will report *externs should be
> > avoided in .c files* false error. This patch fixes the bug.
> 
> I don't think this is a bug. "extern int foo(void);" and
> "int foo(void);" have the same effect: they declare a function
> prototype that can be called from outside the file.
> We don't want to permit that in QEMU. Either:
>  (1) the function is for use only within this file: the
>  declaration should be "static int foo(void);"
>  (2) the function is for use by other files too: the
>  declaration should be in a header file, not a .c file,
>  so the other files can use it
> 
> Do you have an example of code where this warning is a problem?
Hi Peter,

I understand external functions should be put in header files. But there

is some rare exceptions, take the code segment in 


tcg/mips/tcg-target.inc.c for example,

#if TCG_TARGET_REG_BITS == 32
# define LO_OFF  (MIPS_BE * 4)
# define HI_OFF  (4 - LO_OFF)
#else
/* To assert at compile-time that these values are never used
   for TCG_TARGET_REG_BITS == 64.  */
/* extern */ int link_error(void);
# define LO_OFF  link_error()
# define HI_OFF  link_error()
#endif

In this case, the external funciton is just used to assert at complie-time.


If I make a patch to delete the commented out extern before *int link_error()*,

the checkpatch.pl will complain the  *externs should be avoided in .c files* 


error.

The same usage can also be found in tcg/tcg-op.c,

/* Reduce the number of ifdefs below.  This assumes that all uses of
   TCGV_HIGH and TCGV_LOW are properly protected by a conditional that
   the compiler can eliminate.  */
#if TCG_TARGET_REG_BITS == 64
extern TCGv_i32 TCGV_LOW_link_error(TCGv_i64);
extern TCGv_i32 TCGV_HIGH_link_error(TCGv_i64);
#define TCGV_LOW  TCGV_LOW_link_error
#define TCGV_HIGH TCGV_HIGH_link_error
#endif

I'm not sure if the checkpatch.pl should take these case into consideration. :)

Thanks.





Regards.