Re: [PATCH] x32: Add <asm/unistd_x32.h> and regenerate arch-syscall.h

["H.J. Lu" <hjl.tools@gmail.com>]

On Mon, Aug 24, 2020 at 12:10 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Since __NR_set_thread_area may not be defined in the kernel header file,
> > move the test to tests-internal doesn't solve the problem.
>
> I expect that internal tests use the built-in system call tables, so
> <fixup-asm-unistd.h> should be effective for them (indirectly, after
> regenerating the tables).

<fixup-asm-unistd.h> can't be used to add a syscal number.

> >> But is it really correct to add an unsupported system call definition
> >> for the rest of glibc?  If this is just setting things up for a test,
> >> maybe the __X32_SYSCALL_BIT hack is the right approach after all.
> >> (I don't know the objective of this test.)
> >
> > set_thread_area is supported on x32.  The only thing missing is
> >
> > #define __NR_set_thread_area (__X32_SYSCALL_BIT + 205)
> >
> > in <asm/unistd_x32.h>.
> >
> > Should I update my original patch to
> >
> > #define __NR_set_thread_area (__X32_SYSCALL_BIT + 205)
>
> But set_thread_area is not supported for application use, so it's an
> internal/whitebox test no matter what.

True.

> What exactly are you trying to test?

I am putting tools/testing/selftests/x86/sigreturn.c from Linux kernel
into glibc to test a new arch_prctl syscall for CET:

    ARCH_X86_CET_MMAP_SHSTK:

    /* Allocate a new shadow stack with unsigned long long *addr:
         IN: requested shadow stack size: addr[0].
         IN: The mmap flags: addr[1].
             1. MAP_32BIT
             2. MAP_POPULATE
         OUT: allocated shadow stack address: *addr.
     */

-- 
H.J.