On Fri, 2005-10-21 at 08:46 -0400, Vincent W. Freeh wrote:
> I am trying to understand the Linux addr space. I figured someone might
> be able to shed some light on it. Or at least point me to some sources
> that will help.
>
> I don't understand what is happening with malloc and the heap in my
> process. According to /proc/<pid>/maps the memory from heap to stack
> initially looks like that. I only show the four "maps" from the heap
> and above. (This is a slightly altered form consisting of start_addr,
> end_addr, size_in_pgs, permissions, and path_if_one):
>
> 0x08d42000 - 0x08d63000 (33 pgs) rw-p path `[heap]'
> 0xb7ef8000 - 0xb7ef9000 (1 pgs) rw-p
> 0xb7f09000 - 0xb7f0b000 (2 pgs) rw-p
> 0xbfaf5000 - 0xbfb0b000 (22 pgs) rw-p path `[stack]'
>
> First, please fix any erroneous statements/assumptions above. Next I
> have many questions. A few follow.
>
> * How does the heap work? I learned/teach that heap is a contiguous
> chunk of memory that holds dynamically-allocated memory. Doesn't appear
> to be the case.
that's the old school 1970's stuff
the "heap" is still brk in linux, however there is no 1:1 relation
between heap and malloc. malloc in glibc is implemented both using brk
and mmap, depending on the size of your allocation.
>
> * Man pg says can only mprotect mmap-able pages. But what are these?
> How can I tell?
you need to mmap these yourself to be sure.. eg you cannot mprotect the
output of malloc, at least not reliably. Only of mmap.
>
> * Why does mprotect silently fail?
no it has sideeffects; eg it most likely affects more memory than just
your malloc()'d part
> * I thought brk indicated the top of the heap and that all dynamic
> memory would be between bss end and brk. That's not true. What is brk
> for then?
see definition of heap vs malloc above
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