Re: [PATCH] linux-user: Add syscall dispatch support

[Ilya Leoshkevich]

On Wed, 2025-01-15 at 15:36 +0100, Arusekk via wrote:
> This commit adds support for the `prctl(PR_SET_SYSCALL_DISPATCH)`
> function in the Linux userspace emulator.

Typo: this should be PR_SET_SYSCALL_USER_DISPATCH.

> It is implemented as a fully host-independent function, by forcing a
> SIGSYS early during syscall handling, if the PC is outside the
> allowed
> range.
> 
> Tested on [uglendix][1], will probably also apply to recent versions
> of
> Wine that use syscall dispatch.
> 
> [1]: https://sr.ht/~arusekk/uglendix
> 
> Signed-off-by: Arusekk <floss@arusekk.pl>
> ---
>  linux-user/main.c         |  2 ++
>  linux-user/qemu.h         |  5 +++
>  linux-user/syscall.c      | 64
> ++++++++++++++++++++++++++++++++++++++-
>  linux-user/syscall_defs.h |  6 ++++
>  4 files changed, 76 insertions(+), 1 deletion(-)

[...]

> @@ -13852,12 +13886,34 @@ static abi_long do_syscall1(CPUArchState
> *cpu_env, int num, abi_long arg1,
>      return ret;
>  }
>  
> +static bool sys_dispatch(abi_ulong pc, TaskState *ts)
> +{

What about this line from the kernel implementation?

        if (unlikely(arch_syscall_is_vdso_sigreturn(regs)))
                return false;

I think qemu's vdso implements sigreturn, e.g., in
linux-user/arm/vdso.S.

[...]