Date: Tue, 24 Feb 2009 23:11:15 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: cvs-src-old@freebsd.org Subject: cvs commit: src/sys/boot/i386/btx/btx btx.S Message-ID: <200902242311.n1ONBVIb047417@repoman.freebsd.org>
next in thread | raw e-mail | index | archive | help
jhb 2009-02-24 23:11:15 UTC
FreeBSD src repository
Modified files:
sys/boot/i386/btx/btx btx.S
Log:
SVN rev 189017 on 2009-02-24 23:11:15Z by jhb
Fix some more issues with the real mode BTX.
The old BTX passed the general purpose registers from the 32-bit client to
the routines called via virtual 86 mode. The new BTX did the same thing.
However, it turns out that some instructions behave differently in virtual 86
mode and real mode (even though this is under-documented). For example, the
LEAVE instruction will cause an exception in real mode if any of the upper
16-bits of %ebp are non-zero after it executes. In virtual 8086 mode the
upper 16-bits are simply ignored. This could cause faults in hardware
interrupt handlers that inherited an %ebp larger than 0xffff from the 32-bit
client (loader, boot2, etc.) while running in real mode.
To fix, when executing hardware interrupt handlers provide an explicit clean
state where all the general purpose and segment registers are zero upon
entry to the interrupt handler. While here, I attempted to simplify the
control flow in the 'intusr' code that sets up the various stack frames
and exits protected mode to invoke the requested routine via real mode.
A huge thanks to Tor Egge (tegge@) for debugging this issue.
Submitted by: tegge
Reviewed by: tegge
Tested by: bz
MFC after: 1 week
Revision Changes Path
1.48 +60 -35 src/sys/boot/i386/btx/btx/btx.S
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200902242311.n1ONBVIb047417>