I wanted to move away from the --with-pydebug to a normal python and I failed with:
# emerge dev-lang/python:2.7
* IMPORTANT: 11 news items need reading for repository 'gentoo'.
* Use eselect news to read news items.
Calculating dependencies... done!
Debug memory block at address p=0xa7f5900: API 'o'
80 bytes originally requested
The 7 pad bytes at p-7 are not all FORBIDDENBYTE (0xfb):
at p-7: 0xfb
at p-6: 0xfb
at p-5: 0xfa *** OUCH
at p-4: 0xfb
at p-3: 0xfb
at p-2: 0xfb
at p-1: 0xfb
Because memory is corrupted at the start, the count of bytes requested
may be bogus, and checking the trailing pad bytes may segfault.
The 8 pad bytes at tail=0xa7f5950 are FORBIDDENBYTE, as expected.
The block was made by call #21242094 to debug malloc/realloc.
Data at p: 73 00 00 00 79 00 00 00 ... 67 00 00 00 00 00 00 00
Fatal Python error: bad leading pad byte
Aborted (core dumped)
#
Great. So, what can we gather now from this? It got overwritten within few dozens of seconds at most since I started emerge. It is in a different memory region (so no memory module HW bug). I am attaching the resolved stacktrace just in case ...