mirror of
git://projects.qi-hardware.com/openwrt-xburst.git
synced 2024-11-30 19:28:26 +02:00
2f006aa5e8
git-svn-id: svn://svn.openwrt.org/openwrt/trunk/openwrt@197 3c298f89-4303-0410-b956-a3cf2f4a3e73
47 lines
1.7 KiB
Diff
47 lines
1.7 KiB
Diff
http://www.linux-mips.org/archives/linux-mips/2004-09/msg00000.html
|
|
|
|
Atsushi Nemoto <anemo@mba.ocn.ne.jp> writes:
|
|
>/ Is this a get_user's problem or gcc's?/
|
|
|
|
The latter. gcc is putting the empty asm:
|
|
|
|
__asm__ ("":"=r" (__gu_val));
|
|
|
|
into the delay slot of the call.
|
|
|
|
Part of the problem is that gcc estimates the length of an asm to be the
|
|
number of instruction separators + 1. This means that it estimates the
|
|
asm above to be one instruction long, which is perhaps a little silly
|
|
for an empty string.
|
|
|
|
But the real problem is that gcc should never trust this estimate anyway,
|
|
since each "instruction" could obviously be a multi-instruction macro.
|
|
gcc should certainly never put asms into delay slots.
|
|
|
|
FWIW, I don't think the bug is specific to 3.3 or 3.4. It could
|
|
probably trigger for other gcc versions too. It is highly dependent
|
|
on scheduling though.
|
|
|
|
The attached 3.4.x patch fixes the problem there, but if you want to work
|
|
around it for old versions, just avoid using empty asms if you can,
|
|
or make them volatile if you can't.
|
|
|
|
Of course, the problem isn't confined to empty asms. If you have an asm
|
|
with a single, multi-instruction macro, gcc might try putting that in a
|
|
delay slot too. You should at least get an assembler warning in that case.
|
|
|
|
Richard
|
|
|
|
|
|
--- gcc-3.4.1/gcc/config/mips/mips.md-orig 2004-09-02 10:38:36.000000000 -0500
|
|
+++ gcc-3.4.1/gcc/config/mips/mips.md 2004-09-02 10:38:42.000000000 -0500
|
|
@@ -251,7 +251,7 @@
|
|
|
|
;; Can the instruction be put into a delay slot?
|
|
(define_attr "can_delay" "no,yes"
|
|
- (if_then_else (and (eq_attr "type" "!branch,call,jump")
|
|
+ (if_then_else (and (eq_attr "type" "!branch,call,jump,multi")
|
|
(and (eq_attr "hazard" "none")
|
|
(eq_attr "single_insn" "yes")))
|
|
(const_string "yes")
|