Re: [PATCH v2 3/5] linux-user/i386: Emulate x86_64 vsyscalls

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> Notice the magic page during translate, much like we already
> do for the arm32 commpage.  At runtime, raise an exception to
> return cpu_loop for emulation.
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/i386/cpu.h          |   1 +
>  linux-user/i386/cpu_loop.c | 105 +++++++++++++++++++++++++++++++++++++
>  target/i386/translate.c    |  16 +++++-
>  3 files changed, 121 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 164d038d1f..3fb2d2a986 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1000,6 +1000,7 @@ typedef uint64_t FeatureWordArray[FEATURE_WORDS];
>  
>  #define EXCP_VMEXIT     0x100 /* only for system emulation */
>  #define EXCP_SYSCALL    0x101 /* only for user emulation */
> +#define EXCP_VSYSCALL   0x102 /* only for user emulation */
>  
>  /* i386-specific interrupt pending bits.  */
>  #define CPU_INTERRUPT_POLL      CPU_INTERRUPT_TGT_EXT_1
> diff --git a/linux-user/i386/cpu_loop.c b/linux-user/i386/cpu_loop.c
> index e217cca5ee..f9bf6cec27 100644
> --- a/linux-user/i386/cpu_loop.c
> +++ b/linux-user/i386/cpu_loop.c
> @@ -92,6 +92,106 @@ static void gen_signal(CPUX86State *env, int sig, int code, abi_ptr addr)
>      queue_signal(env, info.si_signo, QEMU_SI_FAULT, &info);
>  }
>  
> +#ifdef TARGET_X86_64
> +static bool write_ok_or_segv(CPUX86State *env, abi_ptr addr, size_t len)
> +{
> +    /*
> +     * For all the vsyscalls, NULL means "don't write anything" not
> +     * "write it at address 0".
> +     */
> +    if (addr == 0 || access_ok(VERIFY_WRITE, addr, len)) {
> +        return true;
> +    }
> +
> +    env->error_code = PG_ERROR_W_MASK | PG_ERROR_U_MASK;
> +    gen_signal(env, TARGET_SIGSEGV, TARGET_SEGV_MAPERR, addr);
> +    return false;
> +}
> +
> +/*
> + * Since v3.1, the kernel traps and emulates the vsyscall page.
> + * Entry points other than the official generate SIGSEGV.
> + */
> +static void emulate_vsyscall(CPUX86State *env)
> +{
> +    int syscall;
> +    abi_ulong ret;
> +    uint64_t caller;
> +
> +    /*
> +     * Validate the entry point.  We have already validated the page
> +     * during translation, now verify the offset.
> +     */
> +    switch (env->eip & ~TARGET_PAGE_MASK) {
> +    case 0x000:
> +        syscall = TARGET_NR_gettimeofday;
> +        break;
> +    case 0x400:
> +        syscall = TARGET_NR_time;
> +        break;
> +    case 0x800:
> +        syscall = TARGET_NR_getcpu;
> +        break;
> +    default:
> +    sigsegv:

this label looks a little extraneous.

Otherwise:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée