Re: [PATCH] afs: fix no return statement in function returning non-void

[Zheng Zengkai]

Oops, Sorry for the late reply and missing the compilation details.

> On 6/15/21 5:32 PM, Linus Torvalds wrote:
> > On Tue, Jun 15, 2021 at 4:58 PM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
> > > Some implementations of BUG() are macros, not functions,
> > Not "some", I think. Most.
> >
> > > so "unreachable" is not applicable AFAIK.
> > Sure it is. One common pattern is the x86 one:
> >
> >    #define BUG()                                                   \
> >    do {                                                            \
> >            instrumentation_begin();                                \
> >            _BUG_FLAGS(ASM_UD2, 0);                                 \
> >            unreachable();                                          \
> >    } while (0)
> duh.
>
> > and that "unreachable()" is exactly what I'm talking about.
> >
> > So I repeat: what completely broken compiler / config / architecture
> > is it that needs that "return 0" after a BUG() statement?
> I have seen it on ia64 -- most likely GCC 9.3.0, but I'll have to
> double check that.

Actually we build the kernel with the following compiler, config and 
architecture :

powerpc64-linux-gnu-gcc --version
powerpc64-linux-gnu-gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

CONFIG_AFS_FS=y
# CONFIG_AFS_DEBUG is not set
CONFIG_AFS_DEBUG_CURSOR=y

make ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- -j64

...

fs/afs/dir.c: In function ‘afs_dir_set_page_dirty’:
fs/afs/dir.c:51:1: error: no return statement in function returning 
non-void [-Werror=return-type]
   51 | }
      | ^
cc1: some warnings being treated as errors

> > Because that environment is broken, and the warning is bogus and wrong.
> >
> > It might not be the compiler. It might be some architecture that does
> > this wrong. It might be some very particular configuration that does
> > something bad and makes the "unreachable()" not work (or not exist).
> >
> > But *that* is the bug that should be fixed. Not adding a pointless and
> > incorrect line that makes no sense, just to hide the real bug.
> .