Messages in this thread | | | Subject | Re: Understanding Linux addr space, malloc, and heap | From | Arjan van de Ven <> | Date | Fri, 21 Oct 2005 15:00:02 +0200 |
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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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