Date: Tue, 10 Dec 2002 14:57:33 -0500 (EST) From: John Baldwin <jhb@FreeBSD.org> To: Chuck Tuffli <chuck_tuffli@agilent.com> Cc: freebsd-hackers@freebsd.org Subject: RE: registers not saved Message-ID: <XFMail.20021210145733.jhb@FreeBSD.org> In-Reply-To: <20021210154635.GC605@thegrail.rose.agilent.com>
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On 10-Dec-2002 Chuck Tuffli wrote: > I've been chasing down some weird panics in my CAM driver and have > noticed that functions don't seem to save all register values before > they modify them. > > For example, function A uses register ecx to hold the value of a pointer. Part way through, > function A calls function B which uses ecx as a loop index. The bad part is function B never > saves/restores the value of ecx and function A starts dereferencing garbage. > > An informal sampling of my driver seems to indicate that ebx gets > pushed/poped at entry/exit but ecx and edx don't. Does any of this > sound familiar? Thanks! Yes, eax, ebx, and edx are not "call-safe" registers. If you are writing your own function in assembly and you call a function you need to either save those registers yourself or reload their values. If you are writing a function called by other functions your function needs to preserve ebx, ebp, esi, and edi either by saving and restoring them or by not changing their values. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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