Date: Mon, 24 Jul 2000 08:37:55 +1000 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: John Polstra <jdp@polstra.com> Cc: hm@hcs.de, current@FreeBSD.ORG, bde@zeta.org.au Subject: Re: kernel compile failure without -O option Message-ID: <00Jul24.090444est.115291@border.alcanet.com.au> In-Reply-To: <200007200231.TAA15177@vashon.polstra.com>; from jdp@polstra.com on Wed, Jul 19, 2000 at 07:31:12PM -0700 References: <20000719144614.7FE52483D@hcswork.hcs.de> <200007200231.TAA15177@vashon.polstra.com>
next in thread | previous in thread | raw e-mail | index | archive | help
--3MwIy2ne0vdjdPXF
Content-Type: text/plain; charset=us-ascii
On 2000-Jul-19 19:31:12 -0700, John Polstra <jdp@polstra.com> wrote:
>In article <20000719144614.7FE52483D@hcswork.hcs.de>,
>Hellmuth Michaelis <hm@hcs.de> wrote:
>>
>> In the process of tracing down the problem of the kernel panic when booting
>> a kernel with pcvt enabled, i tried to compile a kernel without the -O
>> option to gcc and got this compile failure (sources from 18.7.2000 9:00 MET):
>>
>> cc -c -pipe -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes
>> -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual
>> -fformat-extensions -ansi -nostdinc -I- -I. -I../.. -I../../../include
>> -D_KERNEL -include opt_global.h -elf -mpreferred-stack-boundary=2
>> -fomit-frame-pointer ../../i386/i386/atomic.c
>> In file included from ../../i386/i386/atomic.c:47:
>> machine/atomic.h: In function `atomic_set_char':
>> machine/atomic.h:106: inconsistent operand constraints in an `asm'
>> machine/atomic.h: In function `atomic_clear_char':
>> machine/atomic.h:107: inconsistent operand constraints in an `asm'
>[...]
>
>I have seen that same problem recently in a slightly different
>context. After staring at the code for a very long time, I could
>only conclude that the problem was a bug in gcc.
Last year I did some testing of atomic.h with a variety of gcc
versions (and, following a prod from bde, at a variety of optimisation
levels). At the time, I had great difficulty finding a set of
constraints that would work with both gcc 2.7.2 and egcs, with and
without optimisation.
Attached is a patch to /sys/i386/include/atomic.h,v 1.11 that I
believe solves the problem. This is an adaption of what I did last
year, to include some of Bruce's comments. At this stage, I've only
checked it against gcc version 2.95.2 19991024 (release) - at it
appears in 4.0 and the latest -current, with -O0, -O1 and -O2. An
earlier version[1] worked with 2.7.2, 2.8.1 and ecgs 1.?. I hope to
be able to check it on gcc 2.7.2 and maybe gcc 2.8.1 tonight.
Note that in theory, gcc 2.7.2 needs a second read-only argument with
a "0" constraint. In practice, this doesn't seem to be necessary
since the write-only argument is volatile memory and therefore the
compiler can't optimize out any preceeding read. This shouldn't be
required for later compiler versions since the first argument is
explicitly read-write.
[1] This was sent to Bruce early last October. The changes since
then are:
- Correct `char' case to specify "q" constraint
- Cast result of not (~) to ensure correct operand type.
- Specify `w' in `short' case to correctly print the 16-bit register.
Peter
--3MwIy2ne0vdjdPXF
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment; filename="atomic.patch"
--- /3.0/cvs/src/sys/i386/include/atomic.h Thu May 11 01:27:24 2000
+++ atomic.h Mon Jul 24 08:02:16 2000
@@ -62,7 +62,7 @@
* This allows kernel modules to be portable between UP and SMP systems.
*/
#if defined(KLD_MODULE)
-#define ATOMIC_ASM(NAME, TYPE, OP, V) \
+#define ATOMIC_ASM(NAME, TYPE, OP, V, CLASS) \
extern void atomic_##NAME##_##TYPE(volatile u_##TYPE *p, u_##TYPE v);
#else /* !KLD_MODULE */
@@ -75,77 +75,61 @@
/*
* The assembly is volatilized to demark potential before-and-after side
* effects if an interrupt or SMP collision were to occur.
+ *
+ * GCC 2.8 and later (including EGCS) support read/write operands
+ * using '+' as a constraint modifier.
+ *
+ * Earlier versions of gcc don't allow the '+' and recommend the use
+ * of separate, matching read-only and write-only operands.
+ * Unfortunately, this doesn't appear to work in all cases. On
+ * the assumption that the memory operand is always volatile, it
+ * seems safe to tell gcc that it is write-only. The `volatile'
+ * attribute on the memory operand prohibits any optimization
+ * away of the reference.
+ *
+ * The constraint class for the read operand is passed as a parameter
+ * to the macro because it needs to be different in the char case.
+ * (In theory, it should also be different in the short case, but
+ * gcc doesn't have any constraint classes to specify 16-bit registers).
+ *
+ * Note that gcc doesn't support string glueing for the constraint
+ * expressions, so the common "m" or "i" bits cannot be pulled out.
*/
-#if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ > 9)
-/* egcs 1.1.2+ version */
-#define ATOMIC_ASM(NAME, TYPE, OP, V) \
+#if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 8)
+#define ATOMIC_ASM(NAME, TYPE, OP, V, CLASS) \
static __inline void \
atomic_##NAME##_##TYPE(volatile u_##TYPE *p, u_##TYPE v)\
{ \
- __asm __volatile(MPLOCKED OP \
- : "=m" (*p) \
- : "0" (*p), "ir" (V)); \
+ __asm __volatile(MPLOCKED OP : "+m" (*p) : CLASS (V) : "cc"); \
}
-
-#else
-/* gcc <= 2.8 version */
-#define ATOMIC_ASM(NAME, TYPE, OP, V) \
+#else /* gcc < 2.8 version */
+#define ATOMIC_ASM(NAME, TYPE, OP, V, CLASS) \
static __inline void \
atomic_##NAME##_##TYPE(volatile u_##TYPE *p, u_##TYPE v)\
{ \
- __asm __volatile(MPLOCKED OP \
- : "=m" (*p) \
- : "ir" (V)); \
+ __asm __volatile(MPLOCKED OP : "=m" (*p) : CLASS (V) : "cc"); \
}
#endif
#endif /* KLD_MODULE */
-#if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ > 9)
-
-/* egcs 1.1.2+ version */
-ATOMIC_ASM(set, char, "orb %b2,%0", v)
-ATOMIC_ASM(clear, char, "andb %b2,%0", ~v)
-ATOMIC_ASM(add, char, "addb %b2,%0", v)
-ATOMIC_ASM(subtract, char, "subb %b2,%0", v)
-
-ATOMIC_ASM(set, short, "orw %w2,%0", v)
-ATOMIC_ASM(clear, short, "andw %w2,%0", ~v)
-ATOMIC_ASM(add, short, "addw %w2,%0", v)
-ATOMIC_ASM(subtract, short, "subw %w2,%0", v)
-
-ATOMIC_ASM(set, int, "orl %2,%0", v)
-ATOMIC_ASM(clear, int, "andl %2,%0", ~v)
-ATOMIC_ASM(add, int, "addl %2,%0", v)
-ATOMIC_ASM(subtract, int, "subl %2,%0", v)
-
-ATOMIC_ASM(set, long, "orl %2,%0", v)
-ATOMIC_ASM(clear, long, "andl %2,%0", ~v)
-ATOMIC_ASM(add, long, "addl %2,%0", v)
-ATOMIC_ASM(subtract, long, "subl %2,%0", v)
-
-#else
-
-/* gcc <= 2.8 version */
-ATOMIC_ASM(set, char, "orb %1,%0", v)
-ATOMIC_ASM(clear, char, "andb %1,%0", ~v)
-ATOMIC_ASM(add, char, "addb %1,%0", v)
-ATOMIC_ASM(subtract, char, "subb %1,%0", v)
-
-ATOMIC_ASM(set, short, "orw %1,%0", v)
-ATOMIC_ASM(clear, short, "andw %1,%0", ~v)
-ATOMIC_ASM(add, short, "addw %1,%0", v)
-ATOMIC_ASM(subtract, short, "subw %1,%0", v)
-
-ATOMIC_ASM(set, int, "orl %1,%0", v)
-ATOMIC_ASM(clear, int, "andl %1,%0", ~v)
-ATOMIC_ASM(add, int, "addl %1,%0", v)
-ATOMIC_ASM(subtract, int, "subl %1,%0", v)
-
-ATOMIC_ASM(set, long, "orl %1,%0", v)
-ATOMIC_ASM(clear, long, "andl %1,%0", ~v)
-ATOMIC_ASM(add, long, "addl %1,%0", v)
-ATOMIC_ASM(subtract, long, "subl %1,%0", v)
-
-#endif
+ATOMIC_ASM(set, char, "orb %1,%0", v, "iq")
+ATOMIC_ASM(clear, char, "andb %1,%0", (char)~v, "iq")
+ATOMIC_ASM(add, char, "addb %1,%0", v, "iq")
+ATOMIC_ASM(subtract, char, "subb %1,%0", v, "iq")
+
+ATOMIC_ASM(set, short, "orw %w1,%0", v, "ir")
+ATOMIC_ASM(clear, short, "andw %w1,%0", (short)~v, "ir")
+ATOMIC_ASM(add, short, "addw %w1,%0", v, "ir")
+ATOMIC_ASM(subtract, short, "subw %w1,%0", v, "ir")
+
+ATOMIC_ASM(set, int, "orl %1,%0", v, "ir")
+ATOMIC_ASM(clear, int, "andl %1,%0", ~v, "ir")
+ATOMIC_ASM(add, int, "addl %1,%0", v, "ir")
+ATOMIC_ASM(subtract, int, "subl %1,%0", v, "ir")
+
+ATOMIC_ASM(set, long, "orl %1,%0", v, "ir")
+ATOMIC_ASM(clear, long, "andl %1,%0", ~v, "ir")
+ATOMIC_ASM(add, long, "addl %1,%0", v, "ir")
+ATOMIC_ASM(subtract, long, "subl %1,%0", v, "ir")
#endif /* ! _MACHINE_ATOMIC_H_ */
--3MwIy2ne0vdjdPXF--
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?00Jul24.090444est.115291>