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mem: actually fully fix the heap bug, add comments for future self

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This commit is contained in:
Michael Scire 2021-05-26 23:21:08 -07:00
parent 0f2855ada8
commit df5537b748
1 changed files with 14 additions and 6 deletions
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20
libraries/libstratosphere/source/mem/impl/heap/mem_impl_heap_tls_heap_central.cpp
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@ -976,27 +976,35 @@ namespace ams::mem::impl::heap {
return span; return span;
} }
} else { } else {
/* Save the extents of the free span we found. */
auto * const prev_ptr = span->start.p;
const size_t prev_pages = span->num_pages; const size_t prev_pages = span->num_pages;
/* Allocate a new span struct. */
Span *new_span = this->AllocateSpanStruct(); Span *new_span = this->AllocateSpanStruct();
if (new_span == nullptr) { if (new_span == nullptr) {
return nullptr; return nullptr;
} }
auto new_span_guard = SCOPE_GUARD { this->FreeSpanToSpanPage(new_span); }; auto new_span_guard = SCOPE_GUARD { this->FreeSpanToSpanPage(new_span); };
span = GetSpanFromPointer(std::addressof(this->span_table), span->start.p); /* Allocating the new span potentially invalidates the span we were looking at, so find the span for it in the table. */
const size_t found_pages = span->num_pages; span = GetSpanFromPointer(std::addressof(this->span_table), prev_ptr);
const size_t cur_pages = span->num_pages;
/* If the span was partially allocated, we need to find a new one that's big enough. */
if (found_pages != prev_pages) { if (cur_pages != prev_pages) {
span = this->SearchFreeSpan(num_pages); span = this->SearchFreeSpan(num_pages);
if (span == nullptr) { if (span == nullptr) {
return nullptr; return nullptr;
} }
} }
if (found_pages == prev_pages || num_pages != span->num_pages) { /* If the span is big enough to split (span->num_pages > num_pages), we want to split it. */
/* We're going to use the new span. */ /* span->num_pages > num_pages is true if the span wasn't partially allocated (cur_pages == prev_pages) */
/* OR if the new free span we found has num_pages > num_pages. Note that we know span->num_pages >= num_pages */
/* so this > condition can be expressed as span->num_pages != num_pages. */
if (cur_pages == prev_pages || num_pages != span->num_pages) {
/* We're going to use the new span for our split. */
new_span_guard.Cancel(); new_span_guard.Cancel();
return this->SplitSpan(span, num_pages, new_span); return this->SplitSpan(span, num_pages, new_span);