The pools memory usage calculation was done using ints by default, making
it harder to identify large ones. Let's switch to unsigned long for the
size calculations.
More and more often, core dumps retrieved on systems that build with
-fPIE by default are becoming unexploitable. Even functions and global
symbols get relocated and gdb cannot figure their final position.
Ironically the post_mortem struct lying in its own section that was
meant to ease its finding is not exempt from this problem.
The only remaining way is to inspect the core to search for the
post-mortem magic, figure its offset from the file and look up the
corresponding virtual address with objdump. This is quite a hassle.
This patch implements a simple utility that opens a 64-bit core dump,
scans the program headers looking for a data segment which contains
the post-mortem magic, and prints it on stdout. It also places the
"pm_init" command alone on its own line to ease copy-pasting into the
gdb console. With this, at least the other commands in this directory
work again and allow to inspect the program's state. E.g:
$ ./getpm core.57612
Found post-mortem magic in segment 5:
Core File Offset: 0xfc600 (0xd5000 + 0x27600)
Runtime VAddr: 0x5613e52b6600 (0x5613e528f000 + 0x27600)
Segment Size: 0x28000
In gdb, copy-paste this line:
pm_init 0x5613e52b6600
It's worth noting that the program has so few dependencies that it even
builds with nolibc, allowing to upload a static executable into containers
being debugged and lacking development tools and compilers. The build
procedure is indicated inthe source code.
These is a collection of functions I'm occasionally using to navigate
in core dumps. Only working ones were extracted.
Those requiring knowledge of global variables (e.g. pools, proxy list)
use the one extracted from the post_mortem struct. That one is defined
in post-mortem.gdb and needs to be initialized using "pm_init post_mortem"
or "pm_init <pointer>". From this point a number of global variables are
accessible even if symbols are missing; those ones are then used by other
functions to dump streams, threads, pools, proxies etc.
The files can be sourced or copy-pasted into a gdb session. It's worth
trying to keep them up-to-date, as the old ones used to navigate through
tasks are no longer usable due to massive changes.
