From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47511) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WBGCo-0007kz-HG for qemu-devel@nongnu.org; Wed, 05 Feb 2014 23:04:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WBGCi-00044M-T7 for qemu-devel@nongnu.org; Wed, 05 Feb 2014 23:04:50 -0500 Received: from mail-qc0-f178.google.com ([209.85.216.178]:64775) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WBGCi-00044I-P8 for qemu-devel@nongnu.org; Wed, 05 Feb 2014 23:04:44 -0500 Received: by mail-qc0-f178.google.com with SMTP id m20so2311649qcx.9 for ; Wed, 05 Feb 2014 20:04:44 -0800 (PST) Date: Wed, 5 Feb 2014 23:04:42 -0500 From: Kevin O'Connor Message-ID: <20140206040442.GA5486@morn.localdomain> References: <52F0DE0F.40507@msgid.tls.msk.ru> <20140205174406.GA26098@morn.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140205174406.GA26098@morn.localdomain> Subject: Re: [Qemu-devel] PC-BSD installer does not boot with 1.7.4 (bisected) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Tokarev , Gerd Hoffmann Cc: Daniele Di Proietto , seabios , qemu-devel , Julian Pidancet On Wed, Feb 05, 2014 at 12:44:06PM -0500, Kevin O'Connor wrote: > On Tue, Feb 04, 2014 at 04:33:19PM +0400, Michael Tokarev wrote: > > We have a bugreport in debian, http://bugs.debian.org/737142, > > stating that PC-BSD does not work with seabios-1.7.4 anymore. > > > > I digged in, and found out that it fails only with -vga std > > (cirrus works fine). So I bisected the issue - only changing > > vgabios-stdvga.bin, and found this: [...] > This seems to be similar to the freebsd problem reported last year - > see: > http://lists.gnu.org/archive/html/qemu-stable/2013-03/msg00037.html [...] > (*) The best I can think of is to try and construct some hand crafted > assembler that can catch buggy x86emu emulators and force a failure.. I have put together some assember to try and run-time test for known broken versions of x86emu. This patch to SeaVGABIOS does seem to catch the freebsd issue and in my tests it convinces freebsd to take a different approach. The patch is a bit ugly though. Comments welcome. -Kevin commit e3caa553e940efb6184b30a5637134c4aa9f8b65 Author: Kevin O'Connor Date: Wed Feb 5 22:47:29 2014 -0500 vgabios: Attempt to detect old x86emu and force a fault. Check for cases where the leal instruction does not work. This instruction is known to not be emulated properly on old versions of x86emu. If a broken version of x86emu is found, force a fault that x86emu will easily detect. This should help prevent soft failures when running old software. Signed-off-by: Kevin O'Connor diff --git a/vgasrc/vgaentry.S b/vgasrc/vgaentry.S index 9854448..e246e7c 100644 --- a/vgasrc/vgaentry.S +++ b/vgasrc/vgaentry.S @@ -45,9 +45,27 @@ _rom_header_signature: * Entry points ****************************************************************/ - // This macro is the same as ENTRY_ARG except the "calll" - // instruction is avoided to work around known issues in the - // emulation of some versions of x86emu. + // Force a fault if found to be running on broken x86emu versions. + DECLFUNC x86emu_fault +x86emu_fault: + int $0x03 +1: hlt + jmp 1b + + // This macro implements a call while avoiding instructions + // that old versions of x86emu have problems with. + .macro VGA_CALLL cfunc + // Make sure leal instruction works. + movl $0x8000, %ecx + leal (%ecx, %ecx, 1), %ecx + cmpl $0x10000, %ecx + jne x86emu_fault + // Use callw instead of calll + push %ax + callw \cfunc + .endm + + // This macro is the same as ENTRY_ARG except VGA_CALLL is used. .macro ENTRY_ARG_VGA cfunc cli cld @@ -57,7 +75,7 @@ _rom_header_signature: movl %esp, %ebx // Backup %esp, then zero high bits movzwl %sp, %esp movl %esp, %eax // First arg is pointer to struct bregs - pushw %ax ; callw \cfunc + VGA_CALLL \cfunc movl %ebx, %esp // Restore %esp (including high bits) POPBREGS .endm @@ -103,7 +121,7 @@ entry_10_extrastack: movw %ds, %dx // Setup %ss/%esp and call function movw %dx, %ss movl %eax, %esp - pushw %ax ; callw handle_10 + VGA_CALLL handle_10 movl %esp, %eax // Restore registers and return movw BREGS_size+4(%eax), %ss