[llvm-branch-commits] [llvm] 9ed1927 - [server-llvm-21][MC] Fixing vector overflow

[Tobias Hieta via llvm-branch-commits]

Author: Lydia Kim
Date: 2025-11-27T11:38:40+01:00
New Revision: 9ed1927442a4e8f417dbfeeab342a9be4204198e

URL: https://github.com/llvm/llvm-project/commit/9ed1927442a4e8f417dbfeeab342a9be4204198e
DIFF: https://github.com/llvm/llvm-project/commit/9ed1927442a4e8f417dbfeeab342a9be4204198e.diff

LOG: [server-llvm-21][MC] Fixing vector overflow

Summary:

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:

Differential Revision: https://phabricator.intern.facebook.com/D87662897

Added: 
    

Modified: 
    llvm/include/llvm/MC/MCSection.h
    llvm/lib/MC/MCSection.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/MC/MCSection.h b/llvm/include/llvm/MC/MCSection.h
index 64b13972bfca1..9daaebf7e7935 100644
--- a/llvm/include/llvm/MC/MCSection.h
+++ b/llvm/include/llvm/MC/MCSection.h
@@ -298,8 +298,8 @@ class MCFragment {
 /// data.
 class MCEncodedFragment : public MCFragment {
   uint8_t BundlePadding = 0;
-  uint32_t ContentStart = 0;
-  uint32_t ContentEnd = 0;
+  uint32_t ContentSize = 0;
+  uint64_t ContentStart = 0;
   uint32_t FixupStart = 0;
   uint32_t FixupEnd = 0;
 
@@ -360,22 +360,23 @@ class MCEncodedFragment : public MCFragment {
 
   // Content-related functions manage parent's storage using ContentStart and
   // ContentSize.
-  void clearContents() { ContentEnd = ContentStart; }
+  void clearContents() { ContentSize = 0; }
   // Get a SmallVector reference. The caller should call doneAppending to update
-  // `ContentEnd`.
+  // `ContentSize`.
   SmallVectorImpl<char> &getContentsForAppending() {
     SmallVectorImpl<char> &S = getParent()->ContentStorage;
-    if (LLVM_UNLIKELY(ContentEnd != S.size())) {
+    if (LLVM_UNLIKELY(ContentStart + ContentSize != S.size())) {
       // Move the elements to the end. Reserve space to avoid invalidating
       // S.begin()+I for `append`.
-      auto Size = ContentEnd - ContentStart;
       auto I = std::exchange(ContentStart, S.size());
-      S.reserve(S.size() + Size);
-      S.append(S.begin() + I, S.begin() + I + Size);
+      S.reserve(S.size() + ContentSize);
+      S.append(S.begin() + I, S.begin() + I + ContentSize);
     }
     return S;
   }
-  void doneAppending() { ContentEnd = getParent()->ContentStorage.size(); }
+  void doneAppending() {
+    ContentSize = getParent()->ContentStorage.size() - ContentStart;
+  }
   void appendContents(ArrayRef<char> Contents) {
     getContentsForAppending().append(Contents.begin(), Contents.end());
     doneAppending();
@@ -387,11 +388,11 @@ class MCEncodedFragment : public MCFragment {
   LLVM_ABI void setContents(ArrayRef<char> Contents);
   MutableArrayRef<char> getContents() {
     return MutableArrayRef(getParent()->ContentStorage)
-        .slice(ContentStart, ContentEnd - ContentStart);
+        .slice(ContentStart, ContentSize);
   }
   ArrayRef<char> getContents() const {
     return ArrayRef(getParent()->ContentStorage)
-        .slice(ContentStart, ContentEnd - ContentStart);
+        .slice(ContentStart, ContentSize);
   }
 
   // Fixup-related functions manage parent's storage using FixupStart and
@@ -409,7 +410,7 @@ class MCEncodedFragment : public MCFragment {
         .slice(FixupStart, FixupEnd - FixupStart);
   }
 
-  size_t getSize() const { return ContentEnd - ContentStart; }
+  size_t getSize() const { return ContentSize; }
 };
 
 /// Fragment for data and encoded instructions.

diff  --git a/llvm/lib/MC/MCSection.cpp b/llvm/lib/MC/MCSection.cpp
index a7330692571de..97f591fbf0e28 100644
--- a/llvm/lib/MC/MCSection.cpp
+++ b/llvm/lib/MC/MCSection.cpp
@@ -84,11 +84,11 @@ LLVM_DUMP_METHOD void MCSection::dump(
 
 void MCEncodedFragment::setContents(ArrayRef<char> Contents) {
   auto &S = getParent()->ContentStorage;
-  if (ContentStart + Contents.size() > ContentEnd) {
+  if (Contents.size() > ContentSize) {
     ContentStart = S.size();
     S.resize_for_overwrite(S.size() + Contents.size());
   }
-  ContentEnd = ContentStart + Contents.size();
+  ContentSize = Contents.size();
   llvm::copy(Contents, S.begin() + ContentStart);
 }