Re: [Qemu-devel] [PATCH] linux-user: Fix syscall instruction usermode emulation on X86_64

[Riku Voipio]

On Fri, Aug 08, 2014 at 11:56:54AM +0800, Jincheng Miao wrote:
> Currently syscall instruction is buggy on user mode X86_64,
> the EIP is updated after do_syscall(), that is too late for
> clone(). Because clone() will create a thread at the env->EIP
> (the address of syscall insn), and then child thread enters
> do_syscall() again, that is not expected. Sometimes it is tragic.
> 
> User mode syscall insn emulation is not used MSR, so the
> action should be same to INT 0x80. INT 0x80 will update EIP in
> do_interrupt(), ditto for syscall() for consistency.

Thanks applied to linux-user tree for next pull request.

Riku

> Signed-off-by: Jincheng Miao <address@hidden>
> ---
>  linux-user/main.c        |    1 -
>  target-i386/seg_helper.c |    4 ++--
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/linux-user/main.c b/linux-user/main.c
> index b453a39..472a16d 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -309,7 +309,6 @@ void cpu_loop(CPUX86State *env)
>                                            env->regs[8],
>                                            env->regs[9],
>                                            0, 0);
> -            env->eip = env->exception_next_eip;
>              break;
>  #endif
>          case EXCP0B_NOSEG:
> diff --git a/target-i386/seg_helper.c b/target-i386/seg_helper.c
> index 2d970d0..13eefba 100644
> --- a/target-i386/seg_helper.c
> +++ b/target-i386/seg_helper.c
> @@ -1127,8 +1127,8 @@ static void do_interrupt_user(CPUX86State *env, int 
> intno, int is_int,
>  
>      /* Since we emulate only user space, we cannot do more than
>         exiting the emulation with the suitable exception and error
> -       code */
> -    if (is_int) {
> +       code. So update EIP for INT 0x80 and EXCP_SYSCALL. */
> +    if (is_int || intno == EXCP_SYSCALL) {
>          env->eip = next_eip;
>      }
>  }
> -- 
> 1.7.1
>