Messages in this thread Patch in this message | | | Date | Tue, 12 Feb 2013 16:01:58 -0800 | From | "tip-bot for H. Peter Anvin" <> | Subject | [tip:x86/mm] x86, doc: Clarify the use of asm("%edx") in uaccess.h |
| |
Commit-ID: ff52c3b02b3f73178bfe0c219cd22abdcb0e46c3 Gitweb: http://git.kernel.org/tip/ff52c3b02b3f73178bfe0c219cd22abdcb0e46c3 Author: H. Peter Anvin <hpa@linux.intel.com> AuthorDate: Tue, 12 Feb 2013 15:37:02 -0800 Committer: H. Peter Anvin <hpa@linux.intel.com> CommitDate: Tue, 12 Feb 2013 15:37:02 -0800
x86, doc: Clarify the use of asm("%edx") in uaccess.h
Put in a comment that explains that the use of asm("%edx") in uaccess.h doesn't actually necessarily mean %edx alone.
Cc: Jamie Lokier <jamie@shareable.org> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Russell King <linux@arm.linux.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: H. J. Lu <hjl.tools@gmail.com> Link: http://lkml.kernel.org/r/511ACDFB.1050707@zytor.com Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> --- arch/x86/include/asm/uaccess.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index d710a25..5ee2687 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -148,9 +148,16 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) * * Returns zero on success, or -EFAULT on error. * On error, the variable @x is set to zero. - * + */ +/* * Careful: we have to cast the result to the type of the pointer * for sign reasons. + * + * The use of %edx as the register specifier is a bit of a + * simplification, as gcc only cares about it as the starting point + * and not size: for a 64-bit value it will use %ecx:%edx on 32 bits + * (%ecx being the next register in gcc's x86 register sequence), and + * %rdx on 64 bits. */ #define get_user(x, ptr) \ ({ \ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |