Seventh argument seen in mmap on i386

[Konstantin Belousov]

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.