Date: Thu, 23 Mar 2000 10:29:52 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Jim Mercer <jim@reptiles.org> Cc: hackers@FreeBSD.ORG Subject: Doh, compiler bug... (was Re: possible bug in kernel/if_ether.c) Message-ID: <200003231829.KAA02591@apollo.backplane.com> References: <20000322225639.T983@reptiles.org> <200003230515.VAA96507@apollo.backplane.com> <20000323054731.W983@reptiles.org>
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Ok, lets see what we have here. %ebx is NULL at the point the code fails.
(the <------ below at c01997c8)
%ebx is the 'm' pointer.
if (m->m_len < sizeof(struct arphdr) &&
:0xc0199794 <arpintr+104>: cmpl $0x7,0xc(%ebx)
:0xc0199798 <arpintr+108>: ja 0xc01997c8 <arpintr+156>
:0xc019979a <arpintr+110>: pushl $0x8
:0xc019979c <arpintr+112>: pushl %ebx
(m = m_pullup(m, sizeof(struct arphdr)) == NULL)) {
:0xc019979d <arpintr+113>: call 0xc016e4b8 <m_pullup>
:0xc01997a2 <arpintr+118>: addl $0x8,%esp
:0xc01997a5 <arpintr+121>: testl %eax,%eax
:0xc01997a7 <arpintr+123>: sete %al
:0xc01997aa <arpintr+126>: movzbl %al,%ebx BING BING BING!
:0xc01997ad <arpintr+129>: testl %ebx,%ebx
The compiler is screwed. The call to m_pullup returns the new 'm'
pointer in %eax. This should be copied to %ebx verbatim.
What the frig is this 'sete' instruction? And the movzbl ? Move byte
to long?
No wonder %ebx is screwed! The compiler is producing shit for code!
Can one of the compiler gurus take a look at this?
Jim, what C flags is make using when you compile up your kernel? Are
you trying to do weird optimizations? I don't see anything in your
kernel config, do you have anything weird in your /etc/make.conf[.local]?
-Matt
:0xc01997af <arpintr+131>: je 0xc01997c8 <arpintr+156>
:0xc01997b1 <arpintr+133>: pushl $0xc024bae0
:0xc01997b6 <arpintr+138>: pushl $0x3
:0xc01997b8 <arpintr+140>: call 0xc015f524 <log>
:0xc01997bd <arpintr+145>: addl $0x8,%esp
:0xc01997c0 <arpintr+148>: jmp 0xc0199731 <arpintr+5>
:0xc01997c5 <arpintr+153>: leal 0x0(%esi),%esi
:0xc01997c8 <arpintr+156>: movl 0x8(%ebx),%ecx <------------
:0xc01997cb <arpintr+159>: movzwl (%ecx),%eax
:0xc01997ce <arpintr+162>: xchgb %ah,%al
:0xc01997d0 <arpintr+164>: cmpw $0x1,%ax
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