Fix jl_gc_internal_obj_base_ptr #50231
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The function `jl_gc_internal_obj_base_ptr` takes a pointer and tries to determine if it is a valid object pointer. As such it has to carefully validate all data it reads, and abort whenever there are obvious inconsistencies. This patch adds a check which aborts when `meta->osize` is zero, just before we perform a division-with-remainder by this value, thus avoiding a potential division-by-zero exception. This fixes a crash we are seeing in our code. The crash did not happen before PR JuliaLang#49644 was merged because back then there was a check for `meta->ages` not being zero, which apparently was enough to detect invalid values for `meta` (e.g. when `meta` points into a null page).
oscardssmith
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The function
jl_gc_internal_obj_base_ptrtakes a pointer and tries to determine if it is a valid object pointer. As such it has to carefully validate all data it reads, and abort whenever there are obvious inconsistencies.This patch adds a check which aborts when
meta->osizeis zero, just before we perform a division-with-remainder by this value, thus avoiding a potential division-by-zero exception. This fixes a crash we are seeing in our code.The crash did not happen before PR #49644 was merged because back then there was a check for
meta->agesnot being zero, which apparently was enough to detect invalid values formeta(e.g. whenmetapoints into a null page).All credits for finding this should go to @benlorenz (see also the discussion at and after oscar-system/GAP.jl#901 (comment)), all misrepresentations are my fault.
Also CC @ThomasBreuer