Re: [PATCH 1/2] x86/x32: Use __x64 prefix for X32 compat syscalls

Andy Lutomirski
2020-06-16T16:49:15Z

On Tue, Jun 16, 2020 at 7:23 AM Brian Gerst <brgerst@gmail.com> wrote:
>
> The ABI prefix for syscalls specifies the argument register mapping, so
> there is no specific reason to continue using the __x32 prefix for the
> compat syscalls. This change will allow using native syscalls in the X32
> specific portion of the syscall table.

Okay, I realize that the x86 syscall machinery is held together by
duct tape and a lot of luck, but:

>
> Signed-off-by: Brian Gerst <brgerst@gmail.com>
> ---
> arch/x86/entry/syscall_x32.c | 8 +++-----
> arch/x86/include/asm/syscall_wrapper.h | 10 +++++-----
> 2 files changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/entry/syscall_x32.c b/arch/x86/entry/syscall_x32.c
> index 3d8d70d3896c..f993e6254043 100644
> --- a/arch/x86/entry/syscall_x32.c
> +++ b/arch/x86/entry/syscall_x32.c
> @@ -9,15 +9,13 @@
> #include <asm/syscall.h>
>
> #define __SYSCALL_64(nr, sym)
> +#define __SYSCALL_COMMON(nr, sym) __SYSCALL_X32(nr, sym)
>
> -#define __SYSCALL_X32(nr, sym) extern long __x32_##sym(const struct pt_regs *);
> -#define __SYSCALL_COMMON(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> +#define __SYSCALL_X32(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> #include <asm/syscalls_64.h>
> #undef __SYSCALL_X32
> -#undef __SYSCALL_COMMON
>
> -#define __SYSCALL_X32(nr, sym) [nr] = __x32_##sym,
> -#define __SYSCALL_COMMON(nr, sym) [nr] = __x64_##sym,
> +#define __SYSCALL_X32(nr, sym) [nr] = __x64_##sym,
>
> asmlinkage const sys_call_ptr_t x32_sys_call_table[__NR_x32_syscall_max+1] = {
> /*
> diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
> index a84333adeef2..267fae9904ff 100644
> --- a/arch/x86/include/asm/syscall_wrapper.h
> +++ b/arch/x86/include/asm/syscall_wrapper.h
> @@ -17,7 +17,7 @@ extern long __ia32_sys_ni_syscall(const struct pt_regs *regs);
> * __x64_sys_*() - 64-bit native syscall
> * __ia32_sys_*() - 32-bit native syscall or common compat syscall
> * __ia32_compat_sys_*() - 32-bit compat syscall

On a 64-bit kernel, an "ia32" compat syscall is __ia32_compat_sys_*, but...

> - * __x32_compat_sys_*() - 64-bit X32 compat syscall
> + * __x64_compat_sys_*() - 64-bit X32 compat syscall

Now an x32 compat syscall is __x64_compat? This seems nonsensical.
I'm also a bit confused as to how this is even necessary for your
other patch.