linux-kernel - Re: Remaining randconfig objtool warnings, linux-next-20200428

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Date:   Wed, 29 Apr 2020 18:01:52 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: Remaining randconfig objtool warnings, linux-next-20200428

On Thu, Apr 30, 2020 at 12:46:57AM +0200, Arnd Bergmann wrote:
> On Wed, Apr 29, 2020 at 8:55 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > On Tue, Apr 28, 2020 at 11:10:44AM -0500, Josh Poimboeuf wrote:
> > > > ==> build/x86/0xE0F2ACFF_defconfig/log <==
> > > > kernel/time/posix-stubs.o: warning: objtool: __x64_sys_timer_create()+0x23: sibling call from callable instruction with modified stack frame
> >
> > This one is fixed with the following cleanup:
> >
> > From: Josh Poimboeuf <jpoimboe@...hat.com>
> > Subject: [PATCH] linkage: Convert syscall alias macros to C
> >
> > There's no need to use inline asm to create ELF alias symbols.
> > Annotated C function declarations can be used instead.
> >
> > This also makes the ordering of the ELF symbol table more logical, with
> > the real function now always coming before the aliases.  This makes it
> > easier for objtool, objdump and other tools to differentiate them.
> >
> > This fixes the following warning:
> >
> >   kernel/time/posix-stubs.o: warning: objtool: __x64_sys_timer_create()+0x23: sibling call from callable instruction with modified stack frame
> >
> > Reported-by: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > ---
> >  include/linux/linkage.h | 14 ++++----------
> >  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> Unfortunately, this patch leads to new warnings when
> CONFIG_POSIX_TIMERS is disabled:

Hm, at least on x86 it seems to build fine without CONFIG_POSIX_TIMERS.
Must be some syscall quirk differences between the arches.

> In file included from /git/arm-soc/kernel/time/posix-stubs.c:9:
> /git/arm-soc/kernel/time/posix-stubs.c:35:37: error: conflicting types
> for 'sys_timer_create'
>    35 | #define SYS_NI(name)  SYSCALL_ALIAS(sys_##name, sys_ni_posix_timers)
>       |                                     ^~~~
> /git/arm-soc/include/linux/linkage.h:26:63: note: in definition of
> macro 'SYSCALL_ALIAS'
>    26 | #define SYSCALL_ALIAS(alias, name) __alias(name) typeof(name) alias
>       |                                                               ^~~~~
> /git/arm-soc/kernel/time/posix-stubs.c:42:1: note: in expansion of
> macro 'SYS_NI'
>    42 | SYS_NI(timer_create);
>       | ^~~~~~
> In file included from /git/arm-soc/kernel/time/posix-stubs.c:13:
> /git/arm-soc/include/linux/syscalls.h:616:17: note: previous
> declaration of 'sys_timer_create' was here
>   616 | asmlinkage long sys_timer_create(clockid_t which_clock,
>       |                 ^~~~~~~~~~~~~~~~
> 
> We can probably move those SYS_NI() instances to kernel/sys_ni.c,
> which does not include the header, but it's still a bit ugly. I'll try
> that tomorrow
> unless you come up with a better suggestion first.
> 
>         Arnd
> 

-- 
Josh