Bug#327351: gcc-4.0: Gcc miscompiles libc on hppa - breaks rounding

["Wesley W. Terpstra" <wesley@terpstra.ca>]

retitle 327351 libc rounding is broken on HPPA

reassign  327351 libc6

tags 327351 +patch

thanks

On Sep 9, 2005, at 3:25 PM, Wesley W. Terpstra wrote:

On Sep 9, 2005, at 3:11 PM, Falk Hueffner wrote:

"Wesley W. Terpstra" <terpstra@debian.org> writes:

  __asm__ ("fstd %%fr0,0(%1)" : "=m" (*sw) : "r" (sw));

  sw[0] &= ~FE_DOWNWARD;

  sw[0] |= round;

  __asm__ ("fldd 0(%0),%%fr0" : : "r" (sw));

This is not a bug in gcc. The second asm is not marked as reading *sw,

so the store can be moved behind it, or omitted if it isn't needed

elsewhere. If you access *sw, you need to tell gcc. So the bug is in

whatever code contains this asm.

I don't know how the __asm__ directive works... "r" isn't for read?

What exactly are you saying should be changed to fix it?

This code is from libc, so if I can verify what you say, I'll reassign the bug.

I tried using 

  __asm__ ("fstd %%fr0,0(%1)" : "=m" (*sw) : "r" (sw));

  sw[BYTE] &= ~FE_DOWNWARD;

  sw[BYTE] |= round;

  __asm__ ("fldd 0(%0), %%fr0" : : "r" (sw), "r" (*sw));

... and it worked.

I don't understand why the *sw needs to be referenced, but you're right

that this fixes the problem. I've attached a patch to fix this in libc.

Attachment: hppa-rounding.patch
Description: Binary data