From 120f07bbc0221cb31877f77d95496badc46cc427 Mon Sep 17 00:00:00 2001
From: Konstantin Baladurin <k.baladurin@partner.samsung.com>
Date: Mon, 14 May 2018 12:35:09 +0300
Subject: PEImageLayout: flush instruction cache only for pages with relocs.

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.
---
 src/vm/peimagelayout.cpp | 46 +++++++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 17 deletions(-)

diff --git a/src/vm/peimagelayout.cpp b/src/vm/peimagelayout.cpp
index a3514e5a06..5f70363f7c 100644
--- a/src/vm/peimagelayout.cpp
+++ b/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);
@@ -259,18 +274,15 @@ void PEImageLayout::ApplyBaseRelocations()
 #ifndef CROSSGEN_COMPILE
     if (dwOldProtection != 0)
     {
-        BOOL bExecRegion = (dwOldProtection & (PAGE_EXECUTE | PAGE_EXECUTE_READ |
-            PAGE_EXECUTE_READWRITE | PAGE_EXECUTE_WRITECOPY)) != 0;
-
         // Restore the protection
         if (!ClrVirtualProtect(pWriteableRegion, cbWriteableRegion,
                                dwOldProtection, &dwOldProtection))
             ThrowLastError();
+    }
 
-        if (bRelocDone && bExecRegion)
-        {
-            ClrFlushInstructionCache(pWriteableRegion, cbWriteableRegion);
-        }
+    if (pFlushRegion != NULL)
+    {
+        ClrFlushInstructionCache(pFlushRegion, cbFlushRegion);
     }
 #endif // CROSSGEN_COMPILE
 }
-- 
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