Date: Wed, 06 Jun 2007 19:24:53 -0400 From: "Dixit, Amol" <dixit@netapp.com> To: freebsd-amd64@freebsd.org Subject: amd64 kmod symbol relocation Message-ID: <46674245.9020304@netapp.com>
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Hi,
I am having issues loading a test module on amd64 platform, ONLY when
its loaded below 2gb (0x80000000).
The module is trying to access a function 'printf()' in a shared library
which is beyond the 2gb boundary but the runtime loader is trying to
relocate the symbol to some other offset in its .text section.
(gdb) disass alloc_loader
Dump of assembler code for function alloc_loader:
0xffffff000b3a2000 <alloc_loader+0>: push %rbp
0xffffff000b3a2001 <alloc_loader+1>: mov $0xb3a2026,%rdi
0xffffff000b3a2008 <alloc_loader+8>: xor %eax,%eax
0xffffff000b3a200a <alloc_loader+10>: mov %rsp,%rbp
0xffffff000b3a200d <alloc_loader+13>: callq 0x8024b730
<---- call printf()
0xffffff000b3a2012 <alloc_loader+18>: leaveq
0xffffff000b3a2013 <alloc_loader+19>: xor %eax,%eax
0xffffff000b3a2015 <alloc_loader+21>: retq
(gdb) p/x frame.tf_rip
$10 = 0xffffff008024b730 <--- panic "privileged
instruction fault" address
(gdb) info sym 0xffffff008024b730
No symbol matches 0xffffff008024b730. <--- nothing here, hence the
panic!
(gdb) info sym 0xffffffff8024b730
printf in section .text <--- here it is!
beyond 2gb (sign-extended)
The module is compiled with kernel memory model (mcmodel=kernel). Any
ideas why the relocation is failing in this manner? How do we force
kldload to use addresses above 2gb?
Object code looks like this:
alloc_loader():
0: 55 push %rbp
1: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
4: R_X86_64_32S .rodata.str1.1+0x6
8: 31 c0 xor %eax,%eax
a: 48 89 e5 mov %rsp,%rbp
d: e8 00 00 00 00 callq 12 <alloc_loader+0x12>
e: R_X86_64_PC32 printf+0xfffffffffffffffc
12: c9 leaveq
13: 31 c0 xor %eax,%eax
15: c3 retq
I believe relocation types R_X86_64_32S and R_X86_64_PC32 require top 33 bits 1 or 0 and in
case of 'printf' 0xffffff008024b730 doesn't obey it...I guess!
Thanks,
Amol
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