From 8391e57b2709b95b7e679c86e738617d99686cd6 Mon Sep 17 00:00:00 2001
From: Fedor <fedor@mail.ru>
Date: Thu, 26 Nov 2020 05:42:11 +0200
Subject: [PATCH] [xpcom] Don't use realloc for shrinking nsTArrays when
 allowRealloc is false.

---
 xpcom/glue/nsTArray-inl.h | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/xpcom/glue/nsTArray-inl.h b/xpcom/glue/nsTArray-inl.h
index 27fd38db0..2eaea8029 100644
--- a/xpcom/glue/nsTArray-inl.h
+++ b/xpcom/glue/nsTArray-inl.h
@@ -248,12 +248,28 @@ nsTArray_base<Alloc, Copy>::ShrinkCapacity(size_type aElemSize,
     return;
   }
 
-  size_type size = sizeof(Header) + length * aElemSize;
-  void* ptr = nsTArrayFallibleAllocator::Realloc(mHdr, size);
-  if (!ptr) {
-    return;
+  size_type newSize = sizeof(Header) + length * aElemSize;
+
+  Header* newHeader;
+  if (!Copy::allowRealloc) {
+    // Malloc() and copy
+    newHeader = static_cast<Header*>(nsTArrayFallibleAllocator::Malloc(newSize));
+    if (!newHeader) {
+      return;
+    }
+
+    Copy::MoveNonOverlappingRegionWithHeader(newHeader, mHdr, Length(), aElemSize);
+
+    nsTArrayFallibleAllocator::Free(mHdr);
+  } else {
+    // Realloc() existing data
+    newHeader = static_cast<Header*>(nsTArrayFallibleAllocator::Realloc(mHdr, newSize));
+    if (!newHeader) {
+      return;
+    }
   }
-  mHdr = static_cast<Header*>(ptr);
+  
+  mHdr = newHeader;
   mHdr->mCapacity = length;
 }