I'm running Arch linux on my laptop, which is kernel 3.12.9 right now. Something has changed about the way the kernel maps in a dynamically-linked executable and I can't figure it out. Here's the example:
% /usr/bin/cat /proc/self/maps ... 00400000-0040b000 r-xp 00000000 08:02 1186756 /usr/bin/cat 0060a000-0060b000 r--p 0000a000 08:02 1186756 /usr/bin/cat 0060b000-0060c000 rw-p 0000b000 08:02 1186756 /usr/bin/cat 00d6c000-00d8d000 rw-p 00000000 00:00 0 [heap] 7f29b3485000-7f29b3623000 r-xp 00000000 08:02 1182988 /usr/lib/libc-2.19.so ...
My question is: what is the third mapping from
readelf -l /usr/bin/cat, there's a loadable segment of 0x1f8 bytes that should map at 0x400000. There's a loadable segment of 0xae10 bytes at 0x60ae10. Those two pieces of file correspond to the 00400000-0040b000 mapping, and the 0060a000-0060b000 mapping. But the third mapping, which claims to be at a file offset of 0xb000 bytes, doesn't seem to correspond to any Elf64_Phdr. In fact, the elf header only has 2 PT_LOAD segments.
I read through
fs/binfm_elf.c in the kernel 3.13.2 source code, and I don't see that the kernel maps in anything other than PT_LOAD segments. If I run
strace -o trace.out /usr/bin/cat /proc/self/maps, I don't see any
mmap() calls that would map in a piece of
/usr/bin/cat, so that 3rd piece is mapped in by the kernel.
I ran the same command (
cat /proc/self/maps) on a RHEL server that was running kernel 2.6.18 + RH patches. That only shows 2 pieces of /usr/bin/cat mapped into memory, so this might be new with kernel 3.x.