[llvm] r267041 - [RuntimeDyld] Fix conservative over-allocation of memory for common symbols.

[Lang Hames via llvm-commits]

Author: lhames
Date: Thu Apr 21 15:08:06 2016
New Revision: 267041

URL: http://llvm.org/viewvc/llvm-project?rev=267041&view=rev
Log:
[RuntimeDyld] Fix conservative over-allocation of memory for common symbols.

The previous allocation code was over-estimating the amount of memory required.

No test case: we don't currently have a good way to detect conervative
over-allocation.


Modified:
    llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

Modified: llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp?rev=267041&r1=267040&r2=267041&view=diff
==============================================================================
--- llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp (original)
+++ llvm/trunk/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp Thu Apr 21 15:08:06 2016
@@ -397,17 +397,24 @@ void RuntimeDyldImpl::computeTotalAllocS
 
   // Compute the size of all common symbols
   uint64_t CommonSize = 0;
+  uint32_t CommonAlign = 1;
   for (symbol_iterator I = Obj.symbol_begin(), E = Obj.symbol_end(); I != E;
        ++I) {
     uint32_t Flags = I->getFlags();
     if (Flags & SymbolRef::SF_Common) {
       // Add the common symbols to a list.  We'll allocate them all below.
       uint64_t Size = I->getCommonSize();
-      CommonSize += Size;
+      uint32_t Align = I->getAlignment();
+      // If this is the first common symbol, use its alignment as the alignment
+      // for the common symbols section.
+      if (CommonSize == 0)
+	CommonAlign = Align;
+      CommonSize = alignTo(CommonSize, Align) + Size;
     }
   }
   if (CommonSize != 0) {
     RWSectionSizes.push_back(CommonSize);
+    RWDataAlign = std::max(RWDataAlign, CommonAlign);
   }
 
   // Compute the required allocation space for each different type of sections
@@ -491,6 +498,7 @@ void RuntimeDyldImpl::emitCommonSymbols(
     return;
 
   uint64_t CommonSize = 0;
+  uint32_t CommonAlign = CommonSymbols.begin()->getAlignment();
   CommonSymbolList SymbolsToAllocate;
 
   DEBUG(dbgs() << "Processing common symbols...\n");
@@ -511,14 +519,16 @@ void RuntimeDyldImpl::emitCommonSymbols(
     uint32_t Align = Sym.getAlignment();
     uint64_t Size = Sym.getCommonSize();
 
-    CommonSize += Align + Size;
+    CommonSize = alignTo(CommonSize, Align) + Size;
+    
     SymbolsToAllocate.push_back(Sym);
   }
 
   // Allocate memory for the section
   unsigned SectionID = Sections.size();
-  uint8_t *Addr = MemMgr.allocateDataSection(CommonSize, sizeof(void *),
-                                             SectionID, StringRef(), false);
+  uint8_t *Addr = MemMgr.allocateDataSection(CommonSize, CommonAlign,
+                                             SectionID, "<common symbols>",
+					     false);
   if (!Addr)
     report_fatal_error("Unable to allocate memory for common symbols!");
   uint64_t Offset = 0;