I'm trying to investigate the state of the C/C++ heap from within gdb on Linux amd64, is there a nice way to do this?
One approach I've tried is to "call mallinfo()" but unfortunately I can't then extract the values I want since gdb doesn't deal with the return value properly.
I'm not easily able to write a function to be compiled into the binary for the process I am attached to, so I can simply implement my own function to extract the values by calling mallinfo() in my own code this way. Is there perhaps a clever trick that will allow me to do this on-the-fly?
Another option could be to locate the heap and traverse the malloc headers / free list; I'd appreciate any pointers to where I could start in finding the location and layout of these.
I've been trying to Google and read around the problem for about 2 hours and I've learnt some fascinating stuff but still not found what I need.
@fd - the RedHat bug had your answer.
The mallinfo
function has been deprecated, and won't be updated. A true query stats API is TDB. Today, you have malloc_stats
and malloc_info
. I can't find any documentation on either one, but here's what they give you.
Is this close enough to what you need?
(gdb) call malloc_stats()
Arena 0:
system bytes = 135168
in use bytes = 96
Total (incl. mmap):
system bytes = 135168
in use bytes = 96
max mmap regions = 0
max mmap bytes = 0
(gdb) call malloc_info(0, stdout)
<malloc version="1">
<heap nr="0">
<sizes>
<unsorted from="1228788" to="1229476" total="3917678" count="3221220448"/>
</sizes>
<total type="fast" count="0" size="0"/>
<total type="rest" count="3221220448" size="3917678"/>
<system type="current" size="135168"/>
<system type="max" size="135168"/>
<aspace type="total" size="135168"/>
<aspace type="mprotect" size="135168"/>
</heap>
<total type="fast" count="0" size="0"/>
<total type="rest" count="3221220448" size="3917678"/>
<system type="current" size="135168
/>
<system type="max" size="135168
/>
<aspace type="total" size="135168"/>
<aspace type="mprotect" size="135168"/>
</malloc>