Replace GCC-specific intrinsic with portable alternative.

Not all supported compilers have GCC intrinsics, so this patch
uses the correct portable alternative.

Additionally, this patch fixes an off-by-one error.  __builtin_ffs
returns the 1-based index of the least-significant 1-bit, but the
function expects the base 2 logarithm of the number, which is
equivalent to the 0-based index of the least-significant 1-bit.

Reviewed by: Keno Fischer

Differential Revision: http://reviews.llvm.org/D4284

llvm-svn: 211669

1 files changed, 5 insertions, 1 deletions

diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index 688b64cca81..bd733c8466b 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -30,6 +30,7 @@
 #include "lldb/Host/Host.h"
 
 #include "llvm/ADT/PointerUnion.h"
+#include "llvm/Support/MathExtras.h"
 
 #define CASE_AND_STREAM(s, def, width)                  \
     case def: s->Printf("%-*s", width, #def); break;
@@ -1227,6 +1228,9 @@ ObjectFileELF::CreateSections(SectionList &unified_section_list)
                     break;
             }
 
+            elf::elf_xword log2align = (header.sh_addralign==0)
+                                        ? 0
+                                        : llvm::Log2_64(header.sh_addralign);
             SectionSP section_sp (new Section(GetModule(),        // Module to which this section belongs.
                                               this,               // ObjectFile to which this section belongs and should read section data from.
                                               SectionIndex(I),    // Section ID.
@@ -1236,7 +1240,7 @@ ObjectFileELF::CreateSections(SectionList &unified_section_list)
                                               vm_size,            // VM size in bytes of this section.
                                               header.sh_offset,   // Offset of this section in the file.
                                               file_size,          // Size of the section as found in the file.
-                                              __builtin_ffs(header.sh_addralign), // Alignment of the section
+                                              log2align,          // Alignment of the section
                                               header.sh_flags));  // Flags for this section.
 
             if (is_thread_specific)