Showing posts with label fpu. Show all posts
Showing posts with label fpu. Show all posts

Saturday, May 21, 2011

Seen a really broken pipe

Have you seen a broken pipe? Sounds like a stupid question for everyone who is working with *NIX. Everyone who has English as a mother tongue, or is old enough to use a non-localized OS has seen a "broken pipe" message. A younger generation might have seen the message in their native language.

Well, that's not the sort of brokenness  I'm talking about.  I mean it more literary:

# echo "This pipe works fine" |cat
This pipe works fine
# echo "And this pipe is veeeeeeeeeeeeeeeeeeeery broken. This pipe is really very broken. Broken." | cat
Ths pip eisveTkebn

Ops. Had to spend a lot of of time in Solaris ascending from SCSI driver (at first I didn't realize that the bug appears in pipes, it looked like a DMA bug) to streams, pipe and so on and then descending to the memcpy which was the source of trouble. It turned out, memcpy uses different routines for small and large data chunks. The small chunks are copied in a loop word-wise and the large ones are copied using VIS instructions (that's SPARC equivalent for Intel's MMX). The emulation of VIS instructions in qemu is buggy, so the memory gets corrupted when these instructions are used.

Once again I'm very impressed that Solaris 2.5.1 - Solaris 7 boots without problems on such a broken hardware. Let's see if  the newer Solaris versions would work with this emulation bug fixed.

Sunday, April 18, 2010

FPU bugs

Found more bugs. This time in FPU. One was very promptly fixed by Blue Swirl (the mysterious qemu-sparc maintainer). Another one is more tricky. qemu goes astray and doesn't stop at breakpoint, so it's gonna be hard to find out what exactly is going on.