[PATCH v4 03/20] powerpc/32: Remove powerpc select specialisation

[Nicholas Piggin]

On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:
> 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/

Seems okay to me, probably Christophe needs to ack it.
Should some of that history be included directly in this changelog?

Should ppc64 compat be added back too, if this is being updated instead
of removed? I don't know much about compat but it seems odd not provide
it (considering it's just using compat_sys_old_select, isn't it?

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>

>
> 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>
> ---
> V1 -> V2: Remove arch-specific select handler
> V2 -> V3: Remove ppc_old_select prototype in <asm/syscalls.h>. Move to
> earlier in patch series
> ---
>  arch/powerpc/include/asm/syscalls.h           |  2 --
>  arch/powerpc/kernel/syscalls.c                | 17 -----------------
>  arch/powerpc/kernel/syscalls/syscall.tbl      |  2 +-
>  .../arch/powerpc/entry/syscalls/syscall.tbl   |  2 +-
>  4 files changed, 2 insertions(+), 21 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/syscalls.h b/arch/powerpc/include/asm/syscalls.h
> index 675a8f5ec3ca..739498c358a1 100644
> --- a/arch/powerpc/include/asm/syscalls.h
> +++ b/arch/powerpc/include/asm/syscalls.h
> @@ -18,8 +18,6 @@ long sys_mmap2(unsigned long addr, size_t len,
>  	       unsigned long fd, unsigned long pgoff);
>  long ppc64_personality(unsigned long personality);
>  long sys_rtas(struct rtas_args __user *uargs);
> -int ppc_select(int n, fd_set __user *inp, fd_set __user *outp,
> -	       fd_set __user *exp, struct __kernel_old_timeval __user *tvp);
>  long ppc_fadvise64_64(int fd, int advice, u32 offset_high, u32 offset_low,
>  		      u32 len_high, u32 len_low);
>  
> diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c
> index fc999140bc27..ef5896bee818 100644
> --- a/arch/powerpc/kernel/syscalls.c
> +++ b/arch/powerpc/kernel/syscalls.c
> @@ -63,23 +63,6 @@ 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
> - */
> -int
> -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
>  long ppc64_personality(unsigned long personality)
>  {
> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index 2600b4237292..4cbbb810ae10 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				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 2600b4237292..4cbbb810ae10 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				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
> -- 
> 2.34.1