Re: [PATCH 06/17] kern/syscall_subr.c: Use copyin()/copyout() to access user memory

[Samuel Thibault]

Sergey Bugaev, le mer. 27 mars 2024 19:18:30 +0300, a ecrit:
> It's not always possible to directly access user memory from kernel
> mode. While it's in theory a lot more expensive to fetch each character
> to be printed separately, mach_print() is only a debugging facility, and
> it's not supposed to be used for printing large amounts of data.

Yes, but the atomicity of mach_print is really useful when debugging
issues with several translators etc.

Could you make it use a buffer so we get atomicity for e.g. a hundred
characters?

Samuel

> ---
>  kern/syscall_subr.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/kern/syscall_subr.c b/kern/syscall_subr.c
> index e0057d94..0027be29 100644
> --- a/kern/syscall_subr.c
> +++ b/kern/syscall_subr.c
> @@ -43,6 +43,7 @@
>  #include <kern/task.h>
>  #include <kern/thread.h>
>  #include <machine/spl.h>     /* for splsched */
> +#include <machine/locore.h>  /* for copyin */
>  
>  #if  MACH_FIXPRI
>  #include <mach/policy.h>
> @@ -381,6 +382,14 @@ thread_depress_abort(thread_t thread)
>  void
>  mach_print(const char *s)
>  {
> -     printf("%s", s);
> +     char    c;
> +     while (TRUE) {
> +             if (copyin(s, &c, 1))
> +                     return;
> +             if (c == 0)
> +                     break;
> +             printf("%c", c);
> +             s++;
> +     }
>  }
>  #endif /* MACH_KDB */
> -- 
> 2.44.0