PEImageLayout: flush instruction cache only for pages with relocs. (dotnet/coreclr...

We need to flush instruction cache only for pages that have relocations
instead of full sections because otherwise application's shared clean
memory is increased in some cases on Linux.

Commit migrated from https://github.com/dotnet/coreclr/commit/539b1745463d697b883ac2c8f556afd82c25b5dc

diff --git a/src/coreclr/src/vm/peimagelayout.cpp b/src/coreclr/src/vm/peimagelayout.cpp
index a3514e5a06005a10d98814ff7c172fb3cc68c975..655c2831ab8b5861cebb7e2d375a1d3e3a9a804a 100644 (file)
--- a/src/coreclr/src/vm/peimagelayout.cpp
+++ b/src/coreclr/src/vm/peimagelayout.cpp
@@ -149,7 +149,10 @@ void PEImageLayout::ApplyBaseRelocations()
     SIZE_T cbWriteableRegion = 0;
     DWORD dwOldProtection = 0;
 
-    BOOL bRelocDone = FALSE;
+    BYTE * pFlushRegion = NULL;
+    SIZE_T cbFlushRegion = 0;
+    // The page size of PE file relocs is always 4096 bytes
+    const SIZE_T cbPageSize = 4096;
 
     COUNT_T dirPos = 0;
     while (dirPos < dirSize)
@@ -184,13 +187,6 @@ void PEImageLayout::ApplyBaseRelocations()
                                        dwOldProtection, &dwOldProtection))
                     ThrowLastError();
 
-                if (bRelocDone && bExecRegion)
-                {
-                    ClrFlushInstructionCache(pWriteableRegion, cbWriteableRegion);
-                }
-
-                bRelocDone = FALSE;
-
                 dwOldProtection = 0;
             }
 
@@ -223,6 +219,7 @@ void PEImageLayout::ApplyBaseRelocations()
             }
         }
 
+        BYTE* pEndAddressToFlush = NULL;
         for (COUNT_T fixupIndex = 0; fixupIndex < fixupsCount; fixupIndex++)
         {
             USHORT fixup = VAL16(fixups[fixupIndex]);
@@ -233,13 +230,13 @@ void PEImageLayout::ApplyBaseRelocations()
             {
             case IMAGE_REL_BASED_PTR:
                 *(TADDR *)address += delta;
-                bRelocDone = TRUE;
+                pEndAddressToFlush = max(pEndAddressToFlush, address + sizeof(TADDR));
                 break;
 
 #ifdef _TARGET_ARM_
             case IMAGE_REL_BASED_THUMB_MOV32:
                 PutThumb2Mov32((UINT16 *)address, GetThumb2Mov32((UINT16 *)address) + delta);
-                bRelocDone = TRUE;
+                pEndAddressToFlush = max(pEndAddressToFlush, address + 8);
                 break;
 #endif
 
@@ -252,6 +249,24 @@ void PEImageLayout::ApplyBaseRelocations()
             }
         }
 
+        BOOL bExecRegion = (dwOldProtection & (PAGE_EXECUTE | PAGE_EXECUTE_READ |
+            PAGE_EXECUTE_READWRITE | PAGE_EXECUTE_WRITECOPY)) != 0;
+
+        if (bExecRegion && pEndAddressToFlush != NULL)
+        {
+            // If the current page is not next to the pending region to flush, flush the current pending region and start a new one
+            if (pageAddress >= pFlushRegion + cbFlushRegion + cbPageSize || pageAddress < pFlushRegion)
+            {
+                if (pFlushRegion != NULL)
+                {
+                    ClrFlushInstructionCache(pFlushRegion, cbFlushRegion);
+                }
+                pFlushRegion = pageAddress;
+            }
+
+            cbFlushRegion = pEndAddressToFlush - pFlushRegion;
+        }
+
         dirPos += fixupsSize;
     }
     _ASSERTE(dirSize == dirPos);
@@ -266,13 +281,13 @@ void PEImageLayout::ApplyBaseRelocations()
         if (!ClrVirtualProtect(pWriteableRegion, cbWriteableRegion,
                                dwOldProtection, &dwOldProtection))
             ThrowLastError();
-
-        if (bRelocDone && bExecRegion)
-        {
-            ClrFlushInstructionCache(pWriteableRegion, cbWriteableRegion);
-        }
     }
 #endif // CROSSGEN_COMPILE
+
+    if (pFlushRegion != NULL)
+    {
+        ClrFlushInstructionCache(pFlushRegion, cbFlushRegion);
+    }
 }
 #endif // FEATURE_PREJIT