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Re: A linuxthreads bug on mips?

To: Ulrich Drepper <drepper@redhat.com>
Subject: Re: A linuxthreads bug on mips?
From: "H . J . Lu" <hjl@lucon.org>
Date: Tue, 29 Jan 2002 18:41:05 -0800
Cc: GNU C Library <libc-alpha@sources.redhat.com>, linux-mips@oss.sgi.com
In-reply-to: <m3zo2x35bi.fsf@myware.mynet>; from drepper@redhat.com on Tue, Jan 29, 2002 at 12:54:41AM -0800
References: <20020125234542.A31028@lucon.org> <m3zo2x35bi.fsf@myware.mynet>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Tue, Jan 29, 2002 at 12:54:41AM -0800, Ulrich Drepper wrote:
> "H . J . Lu" <hjl@lucon.org> writes:
> 
> > Here is a modified ex2.c which only uses one conditional variable. It
> > works fine on x86. But it leads to dead lock on mips where both
> > producer and consumer are suspended. Is this testcase correct?
> 
> 
> Therefore your revised code is not acceptable although it probably
> will almost always work.
> 

It seems that the usage of ll/sc in glibc is wrong when they are used
to implement the compare/set operations. With this patch, the testcase
works now on mips when glibc is compiled with -mips2. Could someone
please double check my changes? If they are really correct, I will
verify other ll/sc usages in glibc.

Thanks.


H.J.
-----. 
2002-01-29  H.J. Lu  <hjl@gnu.org>

        * sysdeps/mips/pt-machine.h (testandset): Return 1 when failed
        to set.
        (__compare_and_swap): Return 0 when failed to compare or swap.

--- linuxthreads/sysdeps/mips/pt-machine.h.llsc Mon Jan 28 18:02:45 2002
+++ linuxthreads/sysdeps/mips/pt-machine.h      Tue Jan 29 16:59:46 2002
@@ -42,16 +42,12 @@ testandset (int *spinlock)
 
   __asm__ __volatile__
     ("/* Inline spinlock test & set */\n\t"
-     "1:\n\t"
      "ll       %0,%3\n\t"
-     ".set     push\n\t"
-     ".set     noreorder\n\t"
-     "bnez     %0,2f\n\t"
-     " li      %1,1\n\t"
-     ".set     pop\n\t"
+     "bnez     %0,1f\n\t"
+     "li       %1,1\n\t"
      "sc       %1,%2\n\t"
-     "beqz     %1,1b\n"
-     "2:\n\t"
+     "sltu     %0,%1,1\n"
+     "1:\n\t"
      "/* End spinlock test & set */"
      : "=&r" (ret), "=&r" (temp), "=m" (*spinlock)
      : "m" (*spinlock)
@@ -84,22 +80,18 @@ register char * stack_pointer __asm__ ("
 PT_EI int
 __compare_and_swap (long int *p, long int oldval, long int newval)
 {
-  long int ret;
+  long int ret, temp;
 
   __asm__ __volatile__
     ("/* Inline compare & swap */\n\t"
+     "move     %0,$0\n\t"
+     "ll       %1,%5\n\t"
+     "bne      %1,%3,1f\n\t"
+     "move     %0,%4\n\t"
+     "sc       %0,%2\n"
      "1:\n\t"
-     "ll       %0,%4\n\t"
-     ".set     push\n"
-     ".set     noreorder\n\t"
-     "bne      %0,%2,2f\n\t"
-     " move    %0,%3\n\t"
-     ".set     pop\n\t"
-     "sc       %0,%1\n\t"
-     "beqz     %0,1b\n"
-     "2:\n\t"
      "/* End compare & swap */"
-     : "=&r" (ret), "=m" (*p)
+     : "=&r" (ret), "=&r" (temp), "=m" (*p)
      : "r" (oldval), "r" (newval), "m" (*p)
      : "memory");
 

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