[PATCH v2 04/14] powerpc/32: Remove powerpc select specialisation

[Christophe Leroy]

Le 25/07/2022 à 08:26, Rohan McLure a écrit :
> Syscall #82 has been implemented for 32-bit platforms in a unique way on
> powerpc systems. This hack will in effect guess whether the caller is
> expecting new select semantics or old select semantics. It does so via a
> guess, based off the first parameter. In new select, this parameter
> represents the length of a user-memory array of file descriptors, and in
> old select this is a pointer to an arguments structure.
> 
> The heuristic simply interprets sufficiently large values of its first
> parameter as being a call to old select. The following is a discussion
> on how this syscall should be handled.
> 
> Link: https://lore.kernel.org/lkml/13737de5-0eb7-e881-9af0-163b0d29a1a0@csgroup.eu/
> 
> As discussed in this thread, the existence of such a hack suggests that for
> whatever powerpc binaries may predate glibc, it is most likely that they
> would have taken use of the old select semantics. x86 and arm64 both
> implement this syscall with oldselect semantics.
> 
> Remove the powerpc implementation, and update syscall.tbl to refer to emit
> a reference to sys_old_select for 32-bit binaries, in keeping with how
> other architectures support syscall #82.
> 
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>

Acked-by: Christophe Leroy <christophe.leroy at csgroup.eu>

> ---
> V1 -> V2: Remove arch-specific select handler
> ---
>   arch/powerpc/kernel/syscalls.c               | 18 ------------------
>   arch/powerpc/kernel/syscalls/syscall.tbl     |  2 +-
>   .../arch/powerpc/entry/syscalls/syscall.tbl  |  2 +-
>   3 files changed, 2 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c
> index 9f339bcb433d..0afbcbd50433 100644
> --- a/arch/powerpc/kernel/syscalls.c
> +++ b/arch/powerpc/kernel/syscalls.c
> @@ -74,24 +74,6 @@ SYSCALL_DEFINE6(mmap, unsigned long, addr, size_t, len,
>   	return do_mmap2(addr, len, prot, flags, fd, offset, PAGE_SHIFT);
>   }
>   
> -#ifdef CONFIG_PPC32
> -/*
> - * Due to some executables calling the wrong select we sometimes
> - * get wrong args.  This determines how the args are being passed
> - * (a single ptr to them all args passed) then calls
> - * sys_select() with the appropriate args. -- Cort
> - */
> -SYSCALL_DEFINE5(ppc_select, int, n, fd_set __user *, inp,
> -		fd_set __user *, outp, fd_set __user *, exp,
> -		struct __kernel_old_timeval __user *, tvp)
> -{
> -	if ((unsigned long)n >= 4096)
> -		return sys_old_select((void __user *)n);
> -
> -	return sys_select(n, inp, outp, exp, tvp);
> -}
> -#endif
> -
>   #ifdef CONFIG_PPC64
>   static inline long do_ppc64_personality(unsigned long personality)
>   {
> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index 59d9259dfbb5..c6cfcdf52c57 100644
> --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> @@ -110,7 +110,7 @@
>   79	common	settimeofday			sys_settimeofday		compat_sys_settimeofday
>   80	common	getgroups			sys_getgroups
>   81	common	setgroups			sys_setgroups
> -82	32	select				sys_ppc_select			sys_ni_syscall
> +82	32	select				sys_old_select			sys_ni_syscall
>   82	64	select				sys_ni_syscall
>   82	spu	select				sys_ni_syscall
>   83	common	symlink				sys_symlink
> diff --git a/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl b/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl
> index 437066f5c4b2..b4c970c9c6b1 100644
> --- a/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl
> +++ b/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl
> @@ -110,7 +110,7 @@
>   79	common	settimeofday			sys_settimeofday		compat_sys_settimeofday
>   80	common	getgroups			sys_getgroups
>   81	common	setgroups			sys_setgroups
> -82	32	select				sys_ppc_select			sys_ni_syscall
> +82	32	select				sys_old_select			sys_ni_syscall
>   82	64	select				sys_ni_syscall
>   82	spu	select				sys_ni_syscall
>   83	common	symlink				sys_symlink