stack size rlimit

[Konstantin Belousov]

On Sun, Sep 21, 2014 at 03:28:38PM -0400, suresh gumpula wrote:
> Hi,
>     I am experimenting the RLIMIT_INFINITY for RLIMIT_STACK and I observed
> that we set to maximize(512M) .
> Looking at kern_setrlimit()  , it seems we are checking this condition and
> reseting to maxssize
> 
> While reading through the "design and implementation of freebsd" book , I
> came across a point that we map the shared libraries just below the stack
> limit.  But looking at sample map of curproc, I don't see shared libraries
> just below the stack limit.
> 
> in linux , we have two different address map layouts , one is  traditional
> layout which maps shared libraries somewhere in the middle and the other
> one which maps just below the stack limit.
> And it seems by default, it  prefers the flexible layout.
> 
> Can somebody please confirm freebsd layout convention. ?
> This is what I see on freebsd, does not look like its starting below the
> stack.

The default mmap() area starts right after the end of the max data
fragment. I.e., it is after the data segment of the main binary +
RLIMIT_DATA.

The runtime linker and kernel image activator (for the interpreter
mapping) utilize default mmap() selection of the address.

You can see this in your map below.
> 
> % cat /proc/curproc/map
> 0x400000 0x403000 3 0 0xffffff0003711d80 r-x 1 0 0x1000 COW NC vnode
> /bin/cat NCH -1
> 0x602000 0x800000 1 0 0xffffff014816aa20 rw- 1 0 0x3000 NCOW NNC default -
> CH 1002
> 0x800602000 0x800638000 34 0 0xffffff0003661ca8 r-x 81 40 0x1004 COW NC
> vnode /libexec/ld-elf.so.1 NCH -1
> 0x800638000 0x800640000 7 0 0xffffff0147f2ee58 rw- 1 0 0x3000 NCOW NNC
> default - CH 1002
> 0x800837000 0x80083b000 4 0 0xffffff0156ec0000 rw- 1 0 0x3000 COW NNC vnode
> /libexec/ld-elf.so.1 CH 1002
> 0x80083b000 0x80084a000 5 0 0xffffff0147fa16c0 rw- 1 0 0x3000 NCOW NNC
> default - CH 1002
> 0x80084a000 0x800984000 116 0 0xffffff00036156c0 r-x 81 40 0x1004 COW NC
> vnode /lib/libc.so.7 NCH -1
> 0x800984000 0x800b84000 0 0 0xffffff0147f32d80 --- 1 0 0x2000 NCOW NNC
> default - NCH -1
> 0x800b84000 0x800b8f000 11 0 0xffffff0147fb7510 rw- 1 0 0x3000 COW NNC
> vnode /lib/libc.so.7 CH 1002
> 0x800b8f000 0x800bf4000 4 0 0xffffff01481676c0 rw- 2 0 0x3000 NCOW NNC
> default - CH 1002
> 0x800c00000 0x800e00000 4 0 0xffffff01481676c0 rw- 2 0 0x3000 NCOW NNC
> default - CH 1002
> 0x7ffffffe0000 0x800000000000 3 0 0xffffff0156e09000 rwx 1 0 0x3000 NCOW
> NNC default - CH 1002
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