Seventh argument seen in mmap on i386

[karnajit wangkhem]

Thanks. That was helpful.

On Tue, May 23, 2017 at 7:36 PM, Konstantin Belousov <kostikbel at gmail.com>
wrote:

> On Tue, May 23, 2017 at 07:25:07PM +0530, karnajit wangkhem wrote:
> > Hi All,
> >
> >
> >
> > I am trying to understand this scenario where a seventh argument is seen
> in
> > case of freebsd.x-i386. As per the mmap man page, the libc function
> > prototype takes in 6 arguments.
> >
> >
> > Ktrace shows the following
> >
> > // Freebsd-11.0 ??? i386 box
> >
> > 44416 a.out    CALL
> > mmap(0,0x1000,0x7<PROT_READ|PROT_WRITE|PROT_EXEC>,0x1002<
> MAP_PRIVATE|MAP_ANON>,0xffffffff,0,0)
> >
> > 44416 a.out    RET   mmap 671535104/0x2806d000
> >
> >
> >
> > // Freebsd-11.0 ??? amd64 box
> >
> > 366 a.out    CALL
> > mmap(0,0x1000,0x7<PROT_READ|PROT_WRITE|PROT_EXEC>,0x1002<
> MAP_PRIVATE|MAP_ANON>,0xffffffff,0)
> >
> > 366 a.out    RET   mmap 34366287872/0x80063f000
> >
> >
> >
> > Also, the disassemble code show that an extra argument was pushed in i386
> > case
> >
> > <SNIP>
> >
> > ->  0x80485e6 <+38>:  movl   %esp, %ebx
> >
> >     0x80485e8 <+40>:  movl   $0x0, 0x18(%ebx)
> >
> >     0x80485ef <+47>:  movl   $0x0, 0x14(%ebx)
> >
> >     0x80485f6 <+54>:  movl   $0xffffffff, 0x10(%ebx)   ; imm = 0xFFFFFFFF
> >
> >     0x80485fd <+61>:  movl   $0x1002, 0xc(%ebx)        ; imm = 0x1002
> >
> >     0x8048604 <+68>:  movl   $0x7, 0x8(%ebx)
> >
> >     0x804860b <+75>:  movl   $0x1000, 0x4(%ebx)        ; imm = 0x1000
> >
> >     0x8048612 <+82>:  movl   $0x0, (%ebx)
> >
> > <SNIP>
> >
> >
> >
> > Please help me understand why this extra argument is seen in case of
> i386.
>
> off_t is 64bit.  It is not seventh arg, it is offset which takes two words.
>