On Tue, Jul 15, 2014 at 12:32 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > 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 seccomp-based syscall > emulation in the fast path. This change is just subtle enough that > I'm keeping it separate. > > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > --- > arch/x86/include/asm/calling.h | 6 +++++- > arch/x86/kernel/entry_64.S | 11 +++-------- > 2 files changed, 8 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h > index cb4c73b..76659b6 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 > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index b25ca96..432c190 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -405,8 +405,8 @@ GLOBAL(system_call_after_swapgs) > * and short: > */ > ENABLE_INTERRUPTS(CLBR_NONE) > - SAVE_ARGS 8,0 > - movq %rax,ORIG_RAX-ARGOFFSET(%rsp) > + SAVE_ARGS 8, 0, rax_enosys=1 > + movq_cfi rax,(ORIG_RAX-ARGOFFSET) I think changing store rax to macro is unnecessary, since it breaks common style of asm with the next line: > movq %rcx,RIP-ARGOFFSET(%rsp) Also it made the diff harder to grasp. The change from the next patch 7/7: > - ja int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */ > + ja int_ret_from_sys_call /* RAX(%rsp) is already set */ probably belongs in this 6/7 patch as well. The rest look good to me. I think it's a big improvement in readability comparing to v1.
