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x86/entry: Do not special-case clone(2) in compat entry

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With the CPU renaming registers on its own, and all the overhead of the
syscall entry/exit, it is doubtful whether the compiled output of

	mov	%r8, %rax
	mov	%rcx, %r8
	mov	%rax, %rcx
	jmpq	sys_clone

is measurably slower than the hand-crafted version of

	xchg	%r8, %rcx

So get rid of this special case.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: luto@amacapital.net
Cc: viro@zeniv.linux.org.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dominik Brodowski 2018-03-06 22:18:08 +01:00 committed by Ingo Molnar
parent 4ddb45db30
commit af52201d99
4 changed files with 14 additions and 13 deletions
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12
arch/x86/entry/entry_64_compat.S
View File

@ -406,15 +406,3 @@ ENTRY(entry_INT80_compat)
TRACE_IRQS_ON
jmp swapgs_restore_regs_and_return_to_usermode
END(entry_INT80_compat)
ENTRY(stub32_clone)
/*
* The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr).
* The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val).
*
* The native 64-bit kernel's sys_clone() implements the latter,
* so we need to swap arguments here before calling it:
*/
xchg %r8, %rcx
jmp sys_clone
ENDPROC(stub32_clone)

2
arch/x86/entry/syscalls/syscall_32.tbl
View File

@ -126,7 +126,7 @@
117 i386 ipc sys_ipc compat_sys_ipc
118 i386 fsync sys_fsync
119 i386 sigreturn sys_sigreturn sys32_sigreturn
120 i386 clone sys_clone stub32_clone
120 i386 clone sys_clone compat_sys_x86_clone
121 i386 setdomainname sys_setdomainname
122 i386 uname sys_newuname
123 i386 modify_ldt sys_modify_ldt

11
arch/x86/ia32/sys_ia32.c
View File

@ -233,3 +233,14 @@ COMPAT_SYSCALL_DEFINE6(x86_fallocate, int, fd, int, mode,
return sys_fallocate(fd, mode, ((u64)offset_hi << 32) | offset_lo,
((u64)len_hi << 32) | len_lo);
}
/*
* The 32-bit clone ABI is CONFIG_CLONE_BACKWARDS
*/
COMPAT_SYSCALL_DEFINE5(x86_clone, unsigned long, clone_flags,
unsigned long, newsp, int __user *, parent_tidptr,
unsigned long, tls_val, int __user *, child_tidptr)
{
return sys_clone(clone_flags, newsp, parent_tidptr, child_tidptr,
tls_val);
}

2
arch/x86/include/asm/sys_ia32.h
View File

@ -55,6 +55,8 @@ asmlinkage long compat_sys_x86_fadvise64(int, unsigned int, unsigned int,
size_t, int);
asmlinkage long compat_sys_x86_fallocate(int, int, unsigned int, unsigned int,
unsigned int, unsigned int);
asmlinkage long compat_sys_x86_clone(unsigned long, unsigned long, int __user *,
unsigned long, int __user *);
/* ia32/ia32_signal.c */
asmlinkage long sys32_sigreturn(void);