On Sun, 08 Dec 2024 19:15:37 +0900,
Hajime Tazaki wrote:
>
> This commit updates the behavior of signal handling under !MMU
> environment. 1) the stack preparation for the signal handlers and
> 2) restoration of stack after rt_sigreturn(2) syscall. Those are needed
> as the stack usage on vfork(2) syscall is different.
>
> It also adds the follow up routine for SIGSEGV as a signal delivery runs
> in the same stack frame while we have to avoid endless SIGSEGV.
(snip)
> diff --git a/arch/x86/um/nommu/signal.c b/arch/x86/um/nommu/signal.c
> new file mode 100644
> index 000000000000..a94e9b86273a
> --- /dev/null
> +++ b/arch/x86/um/nommu/signal.c
> @@ -0,0 +1,43 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/syscalls.h>
> +#include <linux/kernel.h>
> +#include <asm/sigframe.h>
> +
> +#include <sysdep/signal.h>
> +
> +int arch_setup_signal_stack_si(struct rt_sigframe __user **frame,
> + struct ksignal *ksig)
> +{
> + int err = 0;
> +
> + /*
> + * we need to push handler address at top of stack, as
> + * __kernel_vsyscall, called after this returns with ret with
> + * stack contents, thus push the handler here.
> + */
> + *frame = (struct rt_sigframe __user *) ((unsigned long) *frame -
> + sizeof(unsigned long));
> + err |= __put_user((unsigned long)ksig->ka.sa.sa_handler,
> + (unsigned long *)*frame);
> +
> + return err;
this has a serious issue to handle signals.
I also found that manipulation of stack pointer makes the code
cryptic..
I will clean up those parts in the next version.
-- Hajime
