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Fix crash in garbage collector #4941

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Fix crash in garbage collector #4941

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26 changes: 19 additions & 7 deletions src/libexpr/eval.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -233,22 +233,34 @@ static void * oomHandler(size_t requested)
}

class BoehmGCStackAllocator : public StackAllocator {
boost::coroutines2::protected_fixedsize_stack stack {
// We allocate 8 MB, the default max stack size on NixOS.
// A smaller stack might be quicker to allocate but reduces the stack
// depth available for source filter expressions etc.
std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))
boost::coroutines2::protected_fixedsize_stack stack {
// We allocate 8 MB, the default max stack size on NixOS.
// A smaller stack might be quicker to allocate but reduces the stack
// depth available for source filter expressions etc.
std::max(boost::context::stack_traits::default_size(), static_cast<std::size_t>(8 * 1024 * 1024))
};

// This is specific to boost::coroutines2::protected_fixedsize_stack.
// The stack protection page is included in sctx.size, so we have to
// subtract one page size from the stack size.
std::size_t pfss_usable_stack_size(boost::context::stack_context &sctx) {
return sctx.size - boost::context::stack_traits::page_size();
}

public:
boost::context::stack_context allocate() override {
auto sctx = stack.allocate();
GC_add_roots(static_cast<char *>(sctx.sp) - sctx.size, sctx.sp);

// Stacks generally start at a high address and grow to lower addresses.
// Architectures that do the opposite are rare; in fact so rare that
// boost_routine does not implement it.
// So we subtract the stack size.
GC_add_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
return sctx;
}

void deallocate(boost::context::stack_context sctx) override {
GC_remove_roots(static_cast<char *>(sctx.sp) - sctx.size, sctx.sp);
GC_remove_roots(static_cast<char *>(sctx.sp) - pfss_usable_stack_size(sctx), sctx.sp);
stack.deallocate(sctx);
}

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