Previously each malloc size class would keep around a limited number of
unused blocks which were marked with MADV_SET_VOLATILE which could then
be reinitialized when additional blocks were needed.
This changes malloc() so that it also keeps around a number of blocks
without marking them with MADV_SET_VOLATILE. I termed these "hot"
blocks whereas blocks which were marked as MADV_SET_VOLATILE are called
"cold" blocks because they're more expensive to reinitialize.
In the worst case this could increase memory usage per process by
1MB when a program requests a bunch of memory and frees all of it.
Also, in order to make more efficient use of these unused blocks
they're now shared between size classes.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Previous a mallocation was marked as 'reachable' when any other
mallocation or memory region had a pointer to that mallocation. However
there could be the situation that two mallocations have pointers to each
other while still being unreachable from anywhere else. They would be
marked as 'reachable' regardless.
This patch replaces the old way of detemining whether a mallocation is
reachable by analyzing the dependencies of the different mallocations
using a graph-approach. Now mallocations are only reachable if pointed
to by other reachable mallocations or other memory regions.
A nice bonus is that this gets rid of a nested for_each_mallocation, so
the complexity of leak finding becomes linear instead of quadratic.
Accesses in the header (or trailing padding) of a malloc block should
not be associated with any mallocation since only the chunk-sized slots
actually get returned by malloc.
Basically, allow address-to-chunk lookup to fail, and handle such
failures gracefully at call sites.
Fixes#5706.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
