Re: Memory allocations in linux for processes
On 3/19/13, Niroj Pokhrel wrote:
>
> Hi Mulyadi .
> Thank you very much But I still have a minor confusion .
> All I ran was this short program
>
> #include
> int main()
> {
> while(1)
> {
> }
> return 0;
> }
well, before your program is loaded, certainly one or more memory
region must be allocated in RAM, right? if not, where will it be
stored ?
Like Valdis said, strace utility could help you understanding things
during the binary execution. You'll see lots of mmap, I promise :)
--
regards,
Mulyadi Santosa
Freelance Linux trainer and consultant
blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com
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Re: Memory allocations in linux for processes
On Tue, 19 Mar 2013 20:41:55 +0530, Niroj Pokhrel said:
> #include
> int main()
> {
> while(1)
> {
> }
> return 0;
> }
>
> I don't understand where does mmap or malloc come in to play in this code.
Unless you linked it statically, a lot of stuff happens before you ever
get to main() - namely, any shared library linking and mapping. Run
strace on your binary and see how many system calls happen before you hit
the infinite loop.
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Re: Memory allocations in linux for processes
On Tue, Mar 19, 2013 at 8:27 PM, Mulyadi Santosa
wrote:
> Hi Niroj
>
> Please see inlined answer below...
>
> On Mon, Mar 18, 2013 at 5:28 PM, Niroj Pokhrel
> wrote:
> > Hi all,
> > As I have read, whenever we execute a program, the memory is allocated in
> > different sections viz stack, text and data segment.
>
> Yup, that is correct
>
> > But, since we have used
> > loader and linker the three allocations will happen for them too.
>
> Correct again. Linker and loader will be the part of process address space.
>
> > But when I ran a program and did pmap pid, I saw several other fields
> which
> > I have no idea of. What is the [anon] and what is it doing here ?
>
> Anon is short of anonymous. It is a region of memory created by
> function e.g malloc() or mmap()
>
> >Why the
> > memory is being implemented for it and there are so many of them ?
>
> Drawing from above explanation, we can easily conclude somewhere in
> the program, it does malloc() or mmap().
>
> > And also the stack ( 3rd last element), is it the process stack??
>
> Yes, it's process' stack
>
> >Can
> > somebody please explain.
> > Thanking you all in advance.
> >
> > 5448: ./a.out
> > 0040 4K r-x-- /home/n.pokhrel/Personal/mywork/a.out
> > 0060 4K r /home/n.pokhrel/Personal/mywork/a.out
> > 00601000 4K rw--- /home/n.pokhrel/Personal/mywork/a.out
> > 7f57f5e18000 1512K r-x-- /lib/libc-2.11.1.so
> > 7f57f5f92000 2044K - /lib/libc-2.11.1.so
> > 7f57f6191000 16K r /lib/libc-2.11.1.so
> > 7f57f6195000 4K rw--- /lib/libc-2.11.1.so
> > 7f57f6196000 20K rw---[ anon ]
> > 7f57f619b000128K r-x-- /lib/ld-2.11.1.so
> > 7f57f6396000 12K rw---[ anon ]
> > 7f57f63b8000 8K rw---[ anon ]
> > 7f57f63ba000 4K r /lib/ld-2.11.1.so
> > 7f57f63bb000 4K rw--- /lib/ld-2.11.1.so
> > 7f57f63bc000 4K rw---[ anon ]
> > 7fffa2f37000 84K rw---[ stack ]
>
> > 7fffa2fa 4K r-x--[ anon ]
> > ff60 4K r-x--[ anon ]
>
> ok, one of the region above, I think it's VDSO (virtual dynamic shared
> object). It's a region that handle system call. When a process does
> system call, it jumps to VDSO, and it is the VDSO that does the
> actuall syscall
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>
Hi Mulyadi .
Thank you very much But I still have a minor confusion .
All I ran was this short program
#include
int main()
{
while(1)
{
}
return 0;
}
I don't understand where does mmap or malloc come in to play in this code.
It would be great if you can give me some insight.
Thanking you in advance.
Yours,
Niroj Pokhrel
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Re: Memory allocations in linux for processes
Hi Niroj Please see inlined answer below... On Mon, Mar 18, 2013 at 5:28 PM, Niroj Pokhrel wrote: > Hi all, > As I have read, whenever we execute a program, the memory is allocated in > different sections viz stack, text and data segment. Yup, that is correct > But, since we have used > loader and linker the three allocations will happen for them too. Correct again. Linker and loader will be the part of process address space. > But when I ran a program and did pmap pid, I saw several other fields which > I have no idea of. What is the [anon] and what is it doing here ? Anon is short of anonymous. It is a region of memory created by function e.g malloc() or mmap() >Why the > memory is being implemented for it and there are so many of them ? Drawing from above explanation, we can easily conclude somewhere in the program, it does malloc() or mmap(). > And also the stack ( 3rd last element), is it the process stack?? Yes, it's process' stack >Can > somebody please explain. > Thanking you all in advance. > > 5448: ./a.out > 0040 4K r-x-- /home/n.pokhrel/Personal/mywork/a.out > 0060 4K r /home/n.pokhrel/Personal/mywork/a.out > 00601000 4K rw--- /home/n.pokhrel/Personal/mywork/a.out > 7f57f5e18000 1512K r-x-- /lib/libc-2.11.1.so > 7f57f5f92000 2044K - /lib/libc-2.11.1.so > 7f57f6191000 16K r /lib/libc-2.11.1.so > 7f57f6195000 4K rw--- /lib/libc-2.11.1.so > 7f57f6196000 20K rw---[ anon ] > 7f57f619b000128K r-x-- /lib/ld-2.11.1.so > 7f57f6396000 12K rw---[ anon ] > 7f57f63b8000 8K rw---[ anon ] > 7f57f63ba000 4K r /lib/ld-2.11.1.so > 7f57f63bb000 4K rw--- /lib/ld-2.11.1.so > 7f57f63bc000 4K rw---[ anon ] > 7fffa2f37000 84K rw---[ stack ] > 7fffa2fa 4K r-x--[ anon ] > ff60 4K r-x--[ anon ] ok, one of the region above, I think it's VDSO (virtual dynamic shared object). It's a region that handle system call. When a process does system call, it jumps to VDSO, and it is the VDSO that does the actuall syscall -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Memory allocations in linux for processes
Hi all, As I have read, whenever we execute a program, the memory is allocated in different sections viz stack, text and data segment. But, since we have used loader and linker the three allocations will happen for them too. But when I ran a program and did pmap pid, I saw several other fields which I have no idea of. What is the [anon] and what is it doing here ? Why the memory is being implemented for it and there are so many of them ? And also the stack ( 3rd last element), is it the process stack?? Can somebody please explain. Thanking you all in advance. 5448: ./a.out 0040 4K r-x-- /home/n.pokhrel/Personal/mywork/a.out 0060 4K r /home/n.pokhrel/Personal/mywork/a.out 00601000 4K rw--- /home/n.pokhrel/Personal/mywork/a.out 7f57f5e18000 1512K r-x-- /lib/libc-2.11.1.so 7f57f5f92000 2044K - /lib/libc-2.11.1.so 7f57f6191000 16K r /lib/libc-2.11.1.so 7f57f6195000 4K rw--- /lib/libc-2.11.1.so 7f57f6196000 20K rw---[ anon ] 7f57f619b000128K r-x-- /lib/ld-2.11.1.so 7f57f6396000 12K rw---[ anon ] 7f57f63b8000 8K rw---[ anon ] 7f57f63ba000 4K r /lib/ld-2.11.1.so 7f57f63bb000 4K rw--- /lib/ld-2.11.1.so 7f57f63bc000 4K rw---[ anon ] 7fffa2f37000 84K rw---[ stack ] 7fffa2fa 4K r-x--[ anon ] ff60 4K r-x--[ anon ] total ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
