linux-kernel - Re: [PATCH] asm-generic: unistd.h: make 'compat_sys_fadvise64

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Date:   Sun, 7 Aug 2022 15:39:01 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-kernel@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-arch@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [PATCH] asm-generic: unistd.h: make 'compat_sys_fadvise64_64'
 conditional

Hi Arnd,

On 8/7/22 12:44, Arnd Bergmann wrote:
> On Sun, Aug 7, 2022 at 7:28 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>>
>> Don't require 'compat_sys_fadvise64_64' when
>> __ARCH_WANT_COMPAT_FADVISE64_64 is not set.
>>
>> Fixes this build error when CONFIG_ADVISE_SYSCALLS is not set:
>>
>> include/uapi/asm-generic/unistd.h:649:49: error: 'compat_sys_fadvise64_64' undeclared here (not in a function); did you mean 'ksys_fadvise64_64'?
>>   649 | __SC_COMP(__NR3264_fadvise64, sys_fadvise64_64, compat_sys_fadvise64_64)
>> arch/riscv/kernel/compat_syscall_table.c:12:42: note: in definition of macro '__SYSCALL'
>>    12 | #define __SYSCALL(nr, call)      [nr] = (call),
>> include/uapi/asm-generic/unistd.h:649:1: note: in expansion of macro '__SC_COMP'
>>   649 | __SC_COMP(__NR3264_fadvise64, sys_fadvise64_64, compat_sys_fadvise64_64)
>>
>> Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
>> Cc: Paul Walmsley <paul.walmsley@...ive.com>
>> Cc: Palmer Dabbelt <palmer@...belt.com>
>> Cc: Albert Ou <aou@...s.berkeley.edu>
>> Cc: linux-riscv@...ts.infradead.org
>> Cc: Arnd Bergmann <arnd@...db.de>
>> Cc: linux-arch@...r.kernel.org
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: linux-mm@...ck.org
>> ---
>>  include/uapi/asm-generic/unistd.h |    2 ++
>>  1 file changed, 2 insertions(+)
>>
>> --- a/include/uapi/asm-generic/unistd.h
>> +++ b/include/uapi/asm-generic/unistd.h
>> @@ -645,8 +645,10 @@ __SC_COMP(__NR_execve, sys_execve, compa
>>  #define __NR3264_mmap 222
>>  __SC_3264(__NR3264_mmap, sys_mmap2, sys_mmap)
>>  /* mm/fadvise.c */
>> +#ifdef __ARCH_WANT_COMPAT_FADVISE64_64
>>  #define __NR3264_fadvise64 223
>>  __SC_COMP(__NR3264_fadvise64, sys_fadvise64_64, compat_sys_fadvise64_64)
>> +#endif
>>
> 
> This does not work: __ARCH_WANT_COMPAT_FADVISE64_64 is defined in
> arch/riscv/include/asm/unistd.h, which is not a UAPI header. By making the line
> conditional on this, user space no longer sees the macro definition.
> 
> It looks like you also drop the native definition on all architectures other
> than riscv here. What we probably want is to just make all the
> declarations in include/linux/compat.h unconditional and not have them
> depend on architecture specific macros. Some of these may have
> incompatible prototypes depending on the architecture, but if we run
> into those, I would suggest we just give them unique names.

Thanks for the comments.

With the other patch to kernel/sys_ni.c, this one is no longer needed,
although I can look into making more entries in <linux/compat.h>
unconditional. That would also mean adding them to kernel/sys_ni.c, right?
(if not already there)

-- 
~Randy