boehmgc: disable SOFT_VDB on powerpc64le for version 8.2.2 #199978
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Upstream has not yet fixed the bug: ivmai/bdwgc#376 ivmai/bdwgc#479 However there is a recommended workaround: ivmai/bdwgc#479 (comment) This adds `CFLAGS_EXTRA=-DNO_SOFT_VDB` to the `makeFlags`, which prevents direct accesses to `/proc` being used for tracking dirtied pages (which must be rescanned): https://github.com/ivmai/bdwgc/blob/54522af853de28f45195044dadfd795c4e5942aa/include/private/gcconfig.h#L741 The collector will fall back to using mprotect() to trigger page faults on writes to clean pages and maintain its own dirty bits, which is slightly less efficient but (in this case) more reliable. Unreliable page-dirtiness bits can lead to use-after-free() corruption; this is not a situation where disabling the tests is a good idea.
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Nov 7, 2022
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Description of changes
Upstream has not yet fixed the bug:
ivmai/bdwgc#376
ivmai/bdwgc#479
However there is a recommended workaround:
ivmai/bdwgc#479 (comment)
This adds
CFLAGS_EXTRA=-DNO_SOFT_VDBto themakeFlags, which prevents direct accesses to/procbeing used for tracking dirtied pages (which must be rescanned):https://github.com/ivmai/bdwgc/blob/54522af853de28f45195044dadfd795c4e5942aa/include/private/gcconfig.h#L741
The collector will fall back to using mprotect() to trigger page faults on writes to clean pages and maintain its own dirty bits, which is slightly less efficient but (in this case) more reliable. Unreliable page-dirtiness bits can lead to use-after-free() corruption; this is not a situation where disabling the tests is a good idea.
CC: @trofi @jiegec
Things done
nix(with tests enabled)