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Groups > linux.kernel > #1392263
| From | Denys Vlasenko <dvlasenk@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH RESEND] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs |
| Date | 2016-05-02 17:00 +0200 |
| Message-ID | <runuj-5gi-29@gated-at.bofh.it> (permalink) |
| Organization | linux.* mail to news gateway |
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> CC: Ingo Molnar <mingo@kernel.org> CC: Steven Rostedt <rostedt@goodmis.org> CC: Borislav Petkov <bp@alien8.de> CC: "H. Peter Anvin" <hpa@zytor.com> CC: Andy Lutomirski <luto@amacapital.net> CC: Frederic Weisbecker <fweisbec@gmail.com> CC: Will Drewry <wad@chromium.org> CC: Kees Cook <keescook@chromium.org> CC: x86@kernel.org CC: linux-kernel@vger.kernel.org --- Resending. Still applies to current Ingo's tip tree 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 */ -- 1.8.1.4
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[PATCH RESEND] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Denys Vlasenko <dvlasenk@redhat.com> - 2016-05-02 17:00 +0200
Re: [PATCH RESEND] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Andy Lutomirski <luto@kernel.org> - 2016-05-02 20:20 +0200
[tip:x86/asm] x86/asm/entry/32: Simplify pushes of zeroed pt_regs->REGs tip-bot for Denys Vlasenko <tipbot@zytor.com> - 2016-05-03 09:50 +0200
Re: [PATCH RESEND] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Brian Gerst <brgerst@gmail.com> - 2016-05-03 19:50 +0200
Re: [PATCH RESEND] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Andy Lutomirski <luto@amacapital.net> - 2016-05-03 20:00 +0200
Re: [PATCH RESEND] x86/asm/entry/32: simplify pushes of zeroed pt_regs->REGs Brian Gerst <brgerst@gmail.com> - 2016-05-03 20:10 +0200
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