diff options
| author | H. Peter Anvin <hpa@linux.intel.com> | 2013-02-12 15:37:02 -0800 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2013-02-12 15:37:02 -0800 |
| commit | ff52c3b02b3f73178bfe0c219cd22abdcb0e46c3 (patch) | |
| tree | 91f54678d06725e0404853a1bbea30586fdae082 /arch/x86/include | |
| parent | 3578baaed4613a9fc09bab9f79f6ce2ac682e8a3 (diff) | |
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>
Diffstat (limited to 'arch/x86/include')
| -rw-r--r-- | arch/x86/include/asm/uaccess.h | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index d710a2555fd6..5ee26875baea 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) \ ({ \ |