[llvm] r263722 - [COFF] Refactor section alignment calculation

[David Majnemer via llvm-commits]

Author: majnemer
Date: Thu Mar 17 11:55:18 2016
New Revision: 263722

URL: http://llvm.org/viewvc/llvm-project?rev=263722&view=rev
Log:
[COFF] Refactor section alignment calculation

Section alignment isn't completely trivial, let it live in one place so
that we may reuse it in LLVM.

Modified:
    llvm/trunk/include/llvm/Object/COFF.h
    llvm/trunk/lib/Object/COFFObjectFile.cpp

Modified: llvm/trunk/include/llvm/Object/COFF.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Object/COFF.h?rev=263722&r1=263721&r2=263722&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Object/COFF.h (original)
+++ llvm/trunk/include/llvm/Object/COFF.h Thu Mar 17 11:55:18 2016
@@ -414,6 +414,18 @@ struct coff_section {
     return (Characteristics & COFF::IMAGE_SCN_LNK_NRELOC_OVFL) &&
            NumberOfRelocations == UINT16_MAX;
   }
+  uint32_t getAlignment() const {
+    // The IMAGE_SCN_TYPE_NO_PAD bit is a legacy way of getting to
+    // IMAGE_SCN_ALIGN_1BYTES.
+    if (Characteristics & COFF::IMAGE_SCN_TYPE_NO_PAD)
+      return 1;
+
+    // Bit [20:24] contains section alignment. Both 0 and 1 mean alignment 1.
+    uint32_t Shift = (Characteristics >> 20) & 0xF;
+    if (Shift > 0)
+      return 1U << (Shift - 1);
+    return 1;
+  }
 };
 
 struct coff_relocation {
@@ -494,8 +506,11 @@ struct coff_tls_directory {
   support::ulittle32_t SizeOfZeroFill;
   support::ulittle32_t Characteristics;
   uint32_t getAlignment() const {
-    uint32_t AlignBit = (Characteristics & 0x00F00000) >> 20;
-    return AlignBit ? 1 << (AlignBit - 1) : 0;
+    // Bit [20:24] contains section alignment.
+    uint32_t Shift = (Characteristics & 0x00F00000) >> 20;
+    if (Shift > 0)
+      return 1U << (Shift - 1);
+    return 0;
   }
 };
 

Modified: llvm/trunk/lib/Object/COFFObjectFile.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Object/COFFObjectFile.cpp?rev=263722&r1=263721&r2=263722&view=diff
==============================================================================
--- llvm/trunk/lib/Object/COFFObjectFile.cpp (original)
+++ llvm/trunk/lib/Object/COFFObjectFile.cpp Thu Mar 17 11:55:18 2016
@@ -290,7 +290,7 @@ std::error_code COFFObjectFile::getSecti
 
 uint64_t COFFObjectFile::getSectionAlignment(DataRefImpl Ref) const {
   const coff_section *Sec = toSec(Ref);
-  return uint64_t(1) << (((Sec->Characteristics & 0x00F00000) >> 20) - 1);
+  return Sec->getAlignment();
 }
 
 bool COFFObjectFile::isSectionText(DataRefImpl Ref) const {