From: tip-bot for Denys Vlasenko <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: peterz@infradead.org, wad@chromium.org, brgerst@gmail.com,
torvalds@linux-foundation.org, rostedt@goodmis.org,
keescook@chromium.org, fweisbec@gmail.com, bp@alien8.de,
mingo@kernel.org, luto@amacapital.net, hpa@zytor.com,
linux-kernel@vger.kernel.org, dvlasenk@redhat.com,
tglx@linutronix.de, luto@kernel.org
Subject: [tip:x86/asm] x86/asm/entry/32: Simplify pushes of zeroed pt_regs->REGs
Date: Tue, 3 May 2016 00:46:30 -0700 [thread overview]
Message-ID: <tip-778843f934e362ed4ed734520f60a44a78a074b4@git.kernel.org> (raw)
In-Reply-To: <1462201010-16846-1-git-send-email-dvlasenk@redhat.com>
Commit-ID: 778843f934e362ed4ed734520f60a44a78a074b4
Gitweb: http://git.kernel.org/tip/778843f934e362ed4ed734520f60a44a78a074b4
Author: Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Mon, 2 May 2016 16:56:50 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 3 May 2016 08:19:40 +0200
x86/asm/entry/32: Simplify pushes of zeroed pt_regs->REGs
Use of a temporary R8 register here seems to be unnecessary.
"push %r8" is a two-byte insn (it needs REX prefix to specify R8),
"push $0" is two-byte too. It seems just using the latter would be
no worse.
Thus, code had an unnecessary "xorq %r8,%r8" insn.
It probably costs nothing in execution time here since we are probably
limited by store bandwidth at this point, but still.
Run-tested under QEMU: 32-bit calls still work:
/ # ./test_syscall_vdso32
[RUN] Executing 6-argument 32-bit syscall via VDSO
[OK] Arguments are preserved across syscall
[NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn
[OK] R8..R15 did not leak kernel data
[RUN] Executing 6-argument 32-bit syscall via INT 80
[OK] Arguments are preserved across syscall
[OK] R8..R15 did not leak kernel data
[RUN] Running tests under ptrace
[RUN] Executing 6-argument 32-bit syscall via VDSO
[OK] Arguments are preserved across syscall
[NOTE] R11 has changed:0000000000200ed7 - assuming clobbered by SYSRET insn
[OK] R8..R15 did not leak kernel data
[RUN] Executing 6-argument 32-bit syscall via INT 80
[OK] Arguments are preserved across syscall
[OK] R8..R15 did not leak kernel data
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1462201010-16846-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/entry/entry_64_compat.S | 45 +++++++++++++++++++---------------------
1 file changed, 21 insertions(+), 24 deletions(-)
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 847f2f0..e1721da 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -72,24 +72,23 @@ ENTRY(entry_SYSENTER_compat)
pushfq /* pt_regs->flags (except IF = 0) */
orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */
pushq $__USER32_CS /* pt_regs->cs */
- xorq %r8,%r8
- pushq %r8 /* pt_regs->ip = 0 (placeholder) */
+ pushq $0 /* pt_regs->ip = 0 (placeholder) */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
- pushq %r8 /* pt_regs->r8 = 0 */
- pushq %r8 /* pt_regs->r9 = 0 */
- pushq %r8 /* pt_regs->r10 = 0 */
- pushq %r8 /* pt_regs->r11 = 0 */
+ pushq $0 /* pt_regs->r8 = 0 */
+ pushq $0 /* pt_regs->r9 = 0 */
+ pushq $0 /* pt_regs->r10 = 0 */
+ pushq $0 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp (will be overwritten) */
- pushq %r8 /* pt_regs->r12 = 0 */
- pushq %r8 /* pt_regs->r13 = 0 */
- pushq %r8 /* pt_regs->r14 = 0 */
- pushq %r8 /* pt_regs->r15 = 0 */
+ pushq $0 /* pt_regs->r12 = 0 */
+ pushq $0 /* pt_regs->r13 = 0 */
+ pushq $0 /* pt_regs->r14 = 0 */
+ pushq $0 /* pt_regs->r15 = 0 */
cld
/*
@@ -205,17 +204,16 @@ ENTRY(entry_SYSCALL_compat)
pushq %rdx /* pt_regs->dx */
pushq %rbp /* pt_regs->cx (stashed in bp) */
pushq $-ENOSYS /* pt_regs->ax */
- xorq %r8,%r8
- pushq %r8 /* pt_regs->r8 = 0 */
- pushq %r8 /* pt_regs->r9 = 0 */
- pushq %r8 /* pt_regs->r10 = 0 */
- pushq %r8 /* pt_regs->r11 = 0 */
+ pushq $0 /* pt_regs->r8 = 0 */
+ pushq $0 /* pt_regs->r9 = 0 */
+ pushq $0 /* pt_regs->r10 = 0 */
+ pushq $0 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp (will be overwritten) */
- pushq %r8 /* pt_regs->r12 = 0 */
- pushq %r8 /* pt_regs->r13 = 0 */
- pushq %r8 /* pt_regs->r14 = 0 */
- pushq %r8 /* pt_regs->r15 = 0 */
+ pushq $0 /* pt_regs->r12 = 0 */
+ pushq $0 /* pt_regs->r13 = 0 */
+ pushq $0 /* pt_regs->r14 = 0 */
+ pushq $0 /* pt_regs->r15 = 0 */
/*
* User mode is traced as though IRQs are on, and SYSENTER
@@ -316,11 +314,10 @@ ENTRY(entry_INT80_compat)
pushq %rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */
pushq $-ENOSYS /* pt_regs->ax */
- xorq %r8,%r8
- pushq %r8 /* pt_regs->r8 = 0 */
- pushq %r8 /* pt_regs->r9 = 0 */
- pushq %r8 /* pt_regs->r10 = 0 */
- pushq %r8 /* pt_regs->r11 = 0 */
+ pushq $0 /* pt_regs->r8 = 0 */
+ pushq $0 /* pt_regs->r9 = 0 */
+ pushq $0 /* pt_regs->r10 = 0 */
+ pushq $0 /* pt_regs->r11 = 0 */
pushq %rbx /* pt_regs->rbx */
pushq %rbp /* pt_regs->rbp */
pushq %r12 /* pt_regs->r12 */
next prev parent reply other threads:[~2016-05-03 7:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-02 14:56 [PATCH RESEND] x86/asm/entry/32: simplify " Denys Vlasenko
2016-05-02 18:19 ` Andy Lutomirski
2016-05-03 7:46 ` tip-bot for Denys Vlasenko [this message]
2016-05-03 17:45 ` Brian Gerst
2016-05-03 17:55 ` Andy Lutomirski
2016-05-03 18:09 ` Brian Gerst
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