aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/include/asm/alternative.h
diff options
context:
space:
mode:
authorJan Beulich <JBeulich@suse.com>2012-01-20 16:21:41 +0000
committerH. Peter Anvin <hpa@linux.intel.com>2012-01-20 17:29:31 -0800
commit819165fb34b9777f852429f2c6d6f79fbb71b9eb (patch)
tree0ac1aca39cbec9777e902b4393f09e5b0255d42f /arch/x86/include/asm/alternative.h
parentdcd6c92267155e70a94b3927bce681ce74b80d1f (diff)
x86: Adjust asm constraints in atomic64 wrappers
Eric pointed out overly restrictive constraints in atomic64_set(), but there are issues throughout the file. In the cited case, %ebx and %ecx are inputs only (don't get changed by either of the two low level implementations). This was also the case elsewhere. Further in many cases early-clobber indicators were missing. Finally, the previous implementation rolled a custom alternative instruction macro from scratch, rather than using alternative_call() (which was introduced with the commit that the description of the change in question actually refers to). Adjusting has the benefit of not hiding referenced symbols from the compiler, which however requires them to be declared not just in the exporting source file (which, as a desirable side effect, in turn allows that exporting file to become a real 5-line stub). This patch does not eliminate the overly restrictive memory clobbers, however: Doing so would occasionally make the compiler set up a second register for accessing the memory object (to satisfy the added "m" constraint), and it's not clear which of the two non-optimal alternatives is better. v2: Re-do the declaration and exporting of the internal symbols. Reported-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Jan Beulich <jbeulich@suse.com> Link: http://lkml.kernel.org/r/4F19A2A5020000780006E0D9@nat28.tlf.novell.com Cc: Luca Barbieri <luca@luca-barbieri.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/include/asm/alternative.h')
-rw-r--r--arch/x86/include/asm/alternative.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 37ad100a221..49331bedc15 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -145,6 +145,12 @@ static inline int alternatives_text_reserved(void *start, void *end)
*/
#define ASM_OUTPUT2(a...) a
+/*
+ * use this macro if you need clobbers but no inputs in
+ * alternative_{input,io,call}()
+ */
+#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
+
struct paravirt_patch_site;
#ifdef CONFIG_PARAVIRT
void apply_paravirt(struct paravirt_patch_site *start,