Commit-ID: 54eea9957f5763dd1a2555d7e4cb53b4dd389cc6 Gitweb: http://git.kernel.org/tip/54eea9957f5763dd1a2555d7e4cb53b4dd389cc6 Author: Andy Lutomirski <luto@xxxxxxxxxxxxxx> AuthorDate: Fri, 5 Sep 2014 15:13:55 -0700 Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> CommitDate: Mon, 8 Sep 2014 14:14:08 -0700 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 <luto@xxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/01218b493f12ae2f98034b78c9ae085e38e94350.1409954077.git.luto@xxxxxxxxxxxxxx Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> --- arch/x86/include/asm/calling.h | 6 +++++- arch/x86/kernel/entry_64.S | 13 ++++--------- 2 files changed, 9 insertions(+), 10 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 2fac134..0bd6d3c 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -404,8 +404,8 @@ 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) movq %rcx,RIP-ARGOFFSET(%rsp) CFI_REL_OFFSET rip,RIP-ARGOFFSET testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) @@ -417,7 +417,7 @@ system_call_fastpath: andl $__SYSCALL_MASK,%eax cmpl $__NR_syscall_max,%eax #endif - ja badsys + ja ret_from_sys_call /* and return regs->ax */ movq %r10,%rcx call *sys_call_table(,%rax,8) # XXX: rip relative movq %rax,RAX-ARGOFFSET(%rsp) @@ -476,10 +476,6 @@ sysret_signal: FIXUP_TOP_OF_STACK %r11, -ARGOFFSET jmp int_check_syscall_exit_work -badsys: - movq $-ENOSYS,RAX-ARGOFFSET(%rsp) - jmp ret_from_sys_call - #ifdef CONFIG_AUDITSYSCALL /* * Fast path for syscall audit without full syscall trace. @@ -519,7 +515,6 @@ tracesys: jz auditsys #endif SAVE_REST - movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */ FIXUP_TOP_OF_STACK %rdi movq %rsp,%rdi call syscall_trace_enter @@ -536,7 +531,7 @@ tracesys: andl $__SYSCALL_MASK,%eax cmpl $__NR_syscall_max,%eax #endif - ja int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */ + ja int_ret_from_sys_call /* RAX(%rsp) is already set */ movq %r10,%rcx /* fixup for C */ call *sys_call_table(,%rax,8) movq %rax,RAX-ARGOFFSET(%rsp) -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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