Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1215975

Re: [PATCH 0/7] x86 vdso32 cleanups

Show all headers | View raw

On Sat, Aug 29, 2015 at 12:10 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Sat, Aug 29, 2015 at 8:20 AM, Brian Gerst <brgerst@gmail.com> wrote:
>> This patch set contains several cleanups to the 32-bit VDSO.  The
>> main change is to only build one VDSO image, and select the syscall
>> entry point at runtime.
>
> Oh no, we have dueling patches!
>
> I have a 2/3 finished series that cleans up the AT_SYSINFO mess
> differently, as I outlined earlier.  I've only done the compat and
> common bits (no 32-bit native support quite yet), and it enters
> successfully on Intel using SYSENTER and on (fake) AMD using SYSCALL.
> The SYSRET bit isn't there yet.
>
> Other than some ifdeffery, the final system_call.S looks like this:
>
> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/tree/arch/x86/entry/vdso/vdso32/system_call.S?h=x86/entry_compat
>
> The meat is (sorry for whitespace damage):
>
> .text
> .globl __kernel_vsyscall
> .type __kernel_vsyscall,@function
> ALIGN
> __kernel_vsyscall:
> CFI_STARTPROC
> /*
> * Reshuffle regs so that all of any of the entry instructions
> * will preserve enough state.
> */
> pushl %edx
> CFI_ADJUST_CFA_OFFSET 4
> CFI_REL_OFFSET edx, 0
> pushl %ecx
> CFI_ADJUST_CFA_OFFSET 4
> CFI_REL_OFFSET ecx, 0
> movl %esp, %ecx
>
> #ifdef CONFIG_X86_64
> /* If SYSENTER is available, use it. */
> ALTERNATIVE_2 "", "sysenter", X86_FEATURE_SYSENTER32, \
>                  "syscall",  X86_FEATURE_SYSCALL32
> #endif
>
> /* Enter using int $0x80 */
> movl (%esp), %ecx
> int $0x80
> GLOBAL(int80_landing_pad)
>
> /* Restore ECX and EDX in case they were clobbered. */
> popl %ecx
> CFI_RESTORE ecx
> CFI_ADJUST_CFA_OFFSET -4
> popl %edx
> CFI_RESTORE edx
> CFI_ADJUST_CFA_OFFSET -4
> ret
> CFI_ENDPROC
>
> .size __kernel_vsyscall,.-__kernel_vsyscall
> .previous
>
> And that's it.
>
> What do you think?  This comes with massively cleaned up kernel-side
> asm as well as a test case that actually validates the CFI directives.
>
> Certainly, a bunch of your patches make sense regardless, and I'll
> review them and add them to my queue soon.
>
> --Andy

How does the performance compare to the original?  Looking at the
disassembly, there are two added function calls, and it reloads the
args from the stack instead of just shuffling registers.

--
Brian Gerst
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/7] x86 vdso32 cleanups Brian Gerst <brgerst@gmail.com> - 2015-08-29 17:30 +0200
  [PATCH 3/7] x86/vdso32: Remove unused vdso-fakesections.c Brian Gerst <brgerst@gmail.com> - 2015-08-29 17:30 +0200
    Re: [PATCH 3/7] x86/vdso32: Remove unused vdso-fakesections.c Andy Lutomirski <luto@amacapital.net> - 2015-08-30 18:50 +0200
  [PATCH 4/7] x86/vdso32: Build single vdso32 image Brian Gerst <brgerst@gmail.com> - 2015-08-29 17:30 +0200
  [PATCH 6/7] x86/vdso32/xen: Move VDSO_NOTE_NONEGSEG_BIT define Brian Gerst <brgerst@gmail.com> - 2015-08-29 17:30 +0200
  [PATCH 5/7] x86/vdso: Merge 32-bit and 64-bit source files Brian Gerst <brgerst@gmail.com> - 2015-08-29 17:30 +0200
  Re: [PATCH 0/7] x86 vdso32 cleanups Andy Lutomirski <luto@amacapital.net> - 2015-08-29 18:20 +0200
    Re: [PATCH 0/7] x86 vdso32 cleanups Brian Gerst <brgerst@gmail.com> - 2015-08-30 23:20 +0200
      Re: [PATCH 0/7] x86 vdso32 cleanups Andy Lutomirski <luto@amacapital.net> - 2015-08-31 05:00 +0200
        Re: [PATCH 0/7] x86 vdso32 cleanups Andy Lutomirski <luto@amacapital.net> - 2015-09-01 03:40 +0200
          Re: [PATCH 0/7] x86 vdso32 cleanups Andy Lutomirski <luto@amacapital.net> - 2015-09-02 00:00 +0200

csiph-web