From: Parag Warudkar <parag.lkml@gmail.com>
Date: Tue, Apr 13, 2010 at 09:53:46PM -0400
hmm, it doesn't look like it. Your code translates to something like
0: b8 00 00 00 00 mov $0x0,%eax
5: 80 ff ff cmp $0xff,%bh
8: ff 48 21 decl 0x21(%rax)
b: 45 80 48 8b 45 rex.RB orb $0x45,-0x75(%r8)
10: 80 48 ff c8 orb $0xc8,-0x1(%rax)
14: 48 3b 85 40 ff ff ff cmp -0xc0(%rbp),%rax
1b: 48 8b 85 50 ff ff ff mov -0xb0(%rbp),%rax
22: 48 0f 42 7d 80 cmovb -0x80(%rbp),%rdi
27: 48 89 7d 80 mov %rdi,-0x80(%rbp)
2b:* 48 8b 38 mov (%rax),%rdi <-- trapping instruction
2e: 48 85 ff test %rdi,%rdi
31: 0f 84 f5 04 00 00 je 0x52c
37: 48 rex.W
38: b8 fb 0f 00 00 mov $0xffb,%eax
3d: 00 c0 add %al,%al
3f: ff .byte 0xff
which I could correlate with what I get here (comments added):
.loc 1 1051 0
movabsq $549755813888, %rax #, tmp158 PGDIR_SIZE
.LVL392:
leaq (%r12,%rax), %rax #,
movq %rax, -88(%rbp) #, %sfp
movabsq $-549755813888, %rax #, tmp159 PGDIR_MASK
andq %rax, -88(%rbp) # tmp159, %sfp
movq -88(%rbp), %rdx # %sfp, tmp160
movq -72(%rbp), %rax # %sfp, tmp161
decq %rdx # tmp160 __boundary
decq %rax # tmp161 __end
cmpq %rax, %rdx # tmp161, tmp160 rFLAGS
movq -72(%rbp), %rax # %sfp,
cmovb -88(%rbp), %rax # %sfp,,
movq -112(%rbp), %rdx # %sfp, pgd
movq %rax, -88(%rbp) #, %sfp
movq (%rdx), %rax # <variable>.pgd, pgd$pgd
and if this output is correct and if you scroll back a little in your
assemble output, you should probably see that the value computed in
pgd_offset() is being saved in -0x80(%rbp) and reloaded again for use.
So you oops when dereferencing that pgd value in %rax (%rdx in my case),
*pgd in pgd_none_or_clear_bad(pgd) which is called in the below ...
