From a6de5a21fb25cdbbdf3c3e9afd8481581c4f2464 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Tue, 31 Mar 2015 19:00:11 +0200 Subject: [PATCH] x86/asm/entry/64: Use local label to skip around sycall dispatch Logically, we just want to jump around the following instruction and its prologue/epilogue: call *sys_call_table(,%rax,8) if the syscall number is too big - we do not specifically target the "int_ret_from_sys_call" label. Use a local, numerical label for this jump, for more clarity. This also makes the code smaller: -ffffffff8187756b: 0f 87 0f 00 00 00 ja ffffffff81877580 +ffffffff8187756b: 77 0f ja ffffffff8187757c because jumps to global labels are never translated to short jump instructions by GAS. Signed-off-by: Denys Vlasenko Cc: Alexei Starovoitov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Steven Rostedt Cc: Will Drewry Link: http://lkml.kernel.org/r/1427821211-25099-9-git-send-email-dvlasenk@redhat.com [ Improved the changelog. ] Signed-off-by: Ingo Molnar --- arch/x86/kernel/entry_64.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index bad285d84a9f..03c52e217680 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -331,10 +331,11 @@ tracesys_phase2: andl $__SYSCALL_MASK,%eax cmpl $__NR_syscall_max,%eax #endif - ja int_ret_from_sys_call /* RAX(%rsp) is already set */ + ja 1f /* return -ENOSYS (already in pt_regs->ax) */ movq %r10,%rcx /* fixup for C */ call *sys_call_table(,%rax,8) movq %rax,RAX(%rsp) +1: /* Use IRET because user could have changed pt_regs->foo */ /*