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| author | Andy Lutomirski <luto@amacapital.net> | 2014-09-05 15:13:55 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2014-09-08 14:14:08 -0700 |
| commit | 54eea9957f5763dd1a2555d7e4cb53b4dd389cc6 (patch) | |
| tree | 65f301ae08fe3805ee92746e52b6a26139a0b0b9 /arch/x86/kernel | |
| parent | e0ffbaabc46db508b8717f023c0ce03b980eefac (diff) | |
| download | op-kernel-dev-54eea9957f5763dd1a2555d7e4cb53b4dd389cc6.zip op-kernel-dev-54eea9957f5763dd1a2555d7e4cb53b4dd389cc6.tar.gz | |
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@amacapital.net>
Link: http://lkml.kernel.org/r/01218b493f12ae2f98034b78c9ae085e38e94350.1409954077.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/kernel')
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 13 |
1 files changed, 4 insertions, 9 deletions
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) |
