From: David Miller <davem@xxxxxxxxxxxxx>
Date: Mon, 18 Feb 2008 16:43:05 -0800 (PST)
> I think we can fix this easily by using __attribute_const_
> on the print_mac() declaration. Let me play with that.
Actually it seems the 'pure' attribute is more important
here. Although it's not semantically a perfect match,
what we need to tell the compiler is basically that:
1) the return value depends upon the inputs
2) if the input is not used, it's safe to avoid the call
and 'pure' accomplishes that without any unwanted side-effects.
I think this will not result in any unwanted over-optimization.
Because if the inputs change in any way GCC has to emit the
call.
Any objections?
commit 8f789c48448aed74fe1c07af76de8f04adacec7d
Author: David S. Miller <davem@xxxxxxxxxxxxx>
Date: Mon Feb 18 16:50:22 2008 -0800
[NET]: Elminate spurious print_mac() calls.
Patrick McHardy notes that print_mac() can get invoked
even if the result it unused (f.e. as an argument to
pr_debug() when DEBUG is not defined).
Mark this function as "__pure" to eliminate this problem.
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
diff --git a/include/linux/if_ether.h b/include/linux/if_ether.h
index 7a1e011..42dc6a3 100644
--- a/include/linux/if_ether.h
+++ b/include/linux/if_ether.h
@@ -129,7 +129,7 @@ extern ssize_t sysfs_format_mac(char *buf, const unsigned char *addr, int len);
/*
* Display a 6 byte device address (MAC) in a readable format.
*/
-extern char *print_mac(char *buf, const unsigned char *addr);
+extern __pure char *print_mac(char *buf, const unsigned char *addr);
#define MAC_BUF_SIZE 18
#define DECLARE_MAC_BUF(var) char var[MAC_BUF_SIZE] __maybe_unused
-
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