linux-kernel - Re: [RFC 24/30] x86/entry/32: Switch INT80 to the new C syscall path

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Message-ID: <CAMzpN2hXxvzw46oj1_+c41B=iwU=NAb51i3iec7foo8qWOAnNA@mail.gmail.com>
Date:	Thu, 3 Sep 2015 12:45:37 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC 24/30] x86/entry/32: Switch INT80 to the new C syscall path

On Tue, Sep 1, 2015 at 6:41 PM, Andy Lutomirski <luto@...nel.org> wrote:
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/entry/entry_32.S | 34 +++++++++++++---------------------
>  1 file changed, 13 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index 36b6beb181f6..02881e528945 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -153,13 +153,13 @@
>
>  #endif /* CONFIG_X86_32_LAZY_GS */
>
> -.macro SAVE_ALL
> +.macro SAVE_ALL pt_regs_ax=%eax
>         cld
>         PUSH_GS
>         pushl   %fs
>         pushl   %es
>         pushl   %ds
> -       pushl   %eax
> +       pushl   \pt_regs_ax
>         pushl   %ebp
>         pushl   %edi
>         pushl   %esi
> @@ -370,20 +370,17 @@ ENDPROC(entry_SYSENTER_32)
>         # system call handler stub
>  ENTRY(entry_INT80_32)
>         ASM_CLAC
> -       pushl   %eax                            # save orig_eax
> -       SAVE_ALL
> -       GET_THREAD_INFO(%ebp)
> -                                               # system call tracing in operation / emulation
> -       testl   $_TIF_WORK_SYSCALL_ENTRY, TI_flags(%ebp)
> -       jnz     syscall_trace_entry
> -       cmpl    $(NR_syscalls), %eax
> -       jae     syscall_badsys
> -syscall_call:
> -       call    *sys_call_table(, %eax, 4)
> -syscall_after_call:
> -       movl    %eax, PT_EAX(%esp)              # store the return value
> -syscall_exit:
> -       jmp     syscall_exit_work
> +       pushl   %eax                    /* pt_regs->orig_ax */
> +       SAVE_ALL pt_regs_ax=$-ENOSYS    /* save rest, load -ENOSYS into ax */
> +
> +       /*
> +        * User mode is traced as though IRQs are on, and the interrupt gate
> +        * turned them off.
> +        */
> +       TRACE_IRQS_OFF
> +
> +       movl    %esp, %eax
> +       call    do_int80_syscall_32
>
>  restore_all:
>         TRACE_IRQS_IRET
> @@ -491,11 +488,6 @@ syscall_fault:
>         jmp     resume_userspace
>  END(syscall_fault)
>
> -syscall_badsys:
> -       movl    $-ENOSYS, %eax
> -       jmp     syscall_after_call
> -END(syscall_badsys)
> -
>  sysenter_badsys:
>         movl    $-ENOSYS, %eax
>         jmp     sysenter_after_call
> --
> 2.4.3
>

While bisecting a boot failure on the 32-bit native kernel I came
across this build error:
arch/x86/built-in.o: In function `syscall_trace_entry':
/home/bgerst/kernel/linux/arch/x86/entry/entry_32.S:468: undefined
reference to `syscall_call'
/home/bgerst/kernel/linux/arch/x86/entry/entry_32.S:469: undefined
reference to `syscall_exit'

--
Brian Gerst
--
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