Re: NX bit and a.out

[Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost>]

On 13.06.2010 09:56, Brian Marcotte wrote:
> It looks like the recent patches to enable the NX bit on Xen ports has
> broken a.out binaries.
>
> I confirmed that forcing PG_NX to 0 in sys/arch/i386/include/pte.h allows
> a.out programs to work.
>
> Here is a ktrace from a small program.
> [snip]
>    1028      0 mpage.old CALL  mmap(0,0xe0d0,5,4,3,0,0,0)
>    1028      0 mpage.old RET   mmap -1149304832/0xbb7f0000
>    1028      0 mpage.old CALL  mmap(0xbb7fd000,0x1000,3,0x14,3,0,0xd000,0)
>    1028      0 mpage.old RET   mmap -1149251584/0xbb7fd000
>    1028      0 mpage.old CALL  mmap(0xbb7fe000,0xd0,3,0x1014,0xffffffff,0,0,0)
>    1028      0 mpage.old RET   mmap -1149247488/0xbb7fe000
>    1028      0 mpage.old PSIG  SIGSEGV SIG_DFL: code=SEGV_ACCERR, 
> addr=0xbb7fd0e8, trap=6)
>    1028      0 mpage.old NAMI  "mpage.old.core"

Hmm, quick glance, it looks like it requests a map with PROT_EXEC 
(0xe0d0 bytes), mmap() returns address 0xbb7f0000, then it remaps 
0xbb7fd000 => 0xbb7fd000 as just RW, losing execute right in the way.

I'll have a look, thanks for reporting.

--
Jean-Yves Migeon
jeanyves.migeon%free.fr@localhost