From: Chris Packham <judge.packham@gmail.com>
To: u-boot@lists.denx.de
Subject: [U-Boot] [Resend RFC PATCH v2 0/1] MIPS64 timer bug
Date: Tue, 14 Jul 2015 22:54:40 +1200 [thread overview]
Message-ID: <1436871282-5602-1-git-send-email-judge.packham@gmail.com> (raw)
We found this on a custom MIPS64 based board. Basically we were seeing
udelay and friends do odd things occasionally. The problem appears to be
when we read the c0 32-bit counter sometimes we get unexpected values
when this is returned as an unsigned long on a 64-bit system. I've
written a little test program (below) that demonstrates the what I think
is problem, it'll work on a x86_64 desktop. I don't know the ins and
outs of the C specifications to comment on if this is a compiler bug but
I still think we should be treating the c0 registers as unsigned
regardless.
$ cat test.c
#include <stdio.h>
int main(int argc, char *argv[])
{
int a;
unsigned long b;
a = 0x80000000;
b = a;
printf("sizeof(int) = %zu\n", sizeof(int));
printf("sizeof(unsigned long) = %zu\n", sizeof(unsigned long));
printf("a = %d\n", a);
printf("a = %x\n", a);
printf("b = %lu\n", b);
printf("b = %lx\n", b);
return 0;
}
Which yields the following output
$ ./test
sizeof(int) = 4
sizeof(unsigned long) = 8
a = -2147483648
a = 80000000
b = 18446744071562067968
b = ffffffff80000000
And for completeness
$ gcc --version
gcc (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4
Copyright (C) 2013 Free Software Foundation, Inc.
Our embedded target is using
$ mips64-octeon-linux-gnu-gcc --version
mips64-octeon-linux-gnu-gcc (GCC) 4.7.0
Copyright (C) 2012 Free Software Foundation, Inc.
Changes in v2:
- Use Rob's current email address
Chris Packham (1):
mips: Use unsigned int when reading c0 registers
arch/mips/include/asm/mipsregs.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--
2.5.0.rc0
next reply other threads:[~2015-07-14 10:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-14 10:54 Chris Packham [this message]
2015-07-14 10:54 ` [U-Boot] [Resend RFC PATCH v2] mips: Use unsigned int when reading c0 registers Chris Packham
2015-07-14 19:01 ` Daniel Schwierzeck
2015-07-14 21:12 ` Chris Packham
2015-07-16 0:14 ` Chris Packham
2015-07-18 9:29 ` Daniel Schwierzeck
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