From 54eea9957f5763dd1a2555d7e4cb53b4dd389cc6 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Fri, 5 Sep 2014 15:13:55 -0700 Subject: x86_64, entry: Treat regs->ax the same in fastpath and slowpath syscalls For slowpath syscalls, we initialize regs->ax to -ENOSYS and stick the syscall number into regs->orig_ax prior to any possible tracing and syscall execution. This is user-visible ABI used by ptrace syscall emulation and seccomp. For fastpath syscalls, there's no good reason not to do the same thing. It's even slightly simpler than what we're currently doing. It probably has no measureable performance impact. It should have no user-visible effect. The purpose of this patch is to prepare for two-phase syscall tracing, in which the first phase might modify the saved RAX without leaving the fast path. This change is just subtle enough that I'm keeping it separate. Signed-off-by: Andy Lutomirski Link: http://lkml.kernel.org/r/01218b493f12ae2f98034b78c9ae085e38e94350.1409954077.git.luto@amacapital.net Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/calling.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'arch/x86/include/asm/calling.h') diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h index cb4c73bfeb48..76659b67fd11 100644 --- a/arch/x86/include/asm/calling.h +++ b/arch/x86/include/asm/calling.h @@ -85,7 +85,7 @@ For 32-bit we have the following conventions - kernel is built with #define ARGOFFSET R11 #define SWFRAME ORIG_RAX - .macro SAVE_ARGS addskip=0, save_rcx=1, save_r891011=1 + .macro SAVE_ARGS addskip=0, save_rcx=1, save_r891011=1, rax_enosys=0 subq $9*8+\addskip, %rsp CFI_ADJUST_CFA_OFFSET 9*8+\addskip movq_cfi rdi, 8*8 @@ -96,7 +96,11 @@ For 32-bit we have the following conventions - kernel is built with movq_cfi rcx, 5*8 .endif + .if \rax_enosys + movq $-ENOSYS, 4*8(%rsp) + .else movq_cfi rax, 4*8 + .endif .if \save_r891011 movq_cfi r8, 3*8 -- cgit v1.2.2