Messages in this thread | | | Date | Wed, 20 May 2009 21:03:12 +0200 | From | Oleg Nesterov <> | Subject | Q: put_user_try & co (Was: [PATCH 1/5] Split wait_noreap_copyout()) |
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On 05/11, Ingo Molnar wrote: > > See the (new) put_user_try / put_user_ex() / put_user_catch() > abstraction in arch/x86/include/asm/uaccess.h, and how all the x86 > signal code makes use of that to optimize such patterns of per field > user copies.
Just curious, can't we simplify put_user_{try,ex,catch} ?
Pseudo-code:
#define put_user_try \ do { \ __label__ __efault_label; \
#define put_user_catch(err) \ err = 0; \ if (0) { \ __efault_label: \ err = -EFAULT; \ } \ while (0)
#define __put_user_asm_ex(...) \ asm volatile( \ "1: mov ..." \ _ASM_EXTABLE(1b, &__efault_label) \ : : ...)
Now, we don't need thread_info->uaccess_err, and we don't need the special "if (fixup->fixup < 16)" hack in fixup_exception(). Once any put_user_ex() fails, we jump to the __efault_label and set err = -EFAULT.
This also means that we skip other put_user_ex's after the faulted one. Not very important, this is unlikely case, but imho nice anyway.
Can this work? (warning: my asm skills is almost zero ;)
Oleg.
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