Generate optimal string table for section names; align section headers

Author: filipnavara

src/LibObjectFile/Elf/ElfObjectFile.cs

@@ -253,12 +253,23 @@ public unsafe void UpdateLayout(DiagnosticBag diagnostics)
                         shstrTable.Reset();
 
                         // Prepare all section names (to calculate the name indices and the size of the SectionNames)
-                        for (var j = 0; j < sections.Count; j++)
+                        // Do it in two passes to generate optimal string table
+                        for (var pass = 0; pass < 2; pass++)
                         {
-                            var otherSection = sections[j];
-                            if ((j == 0 && otherSection.Type == ElfSectionType.Null)) continue;
-                            if (otherSection.IsShadow) continue;
-                            otherSection.Name = otherSection.Name.WithIndex(shstrTable.GetOrCreateIndex(otherSection.Name));
+                            for (var j = 0; j < sections.Count; j++)
+                            {
+                                var otherSection = sections[j];
+                                if ((j == 0 && otherSection.Type == ElfSectionType.Null)) continue;
+                                if (otherSection.IsShadow) continue;
+                                if (pass == 0)
+                                {
+                                    shstrTable.ReserveString(otherSection.Name);
+                                }
+                                else
+                                {
+                                    otherSection.Name = otherSection.Name.WithIndex(shstrTable.GetOrCreateIndex(otherSection.Name));
+                                }
+                            }
                         }
                     }
 
@@ -276,9 +287,9 @@ public unsafe void UpdateLayout(DiagnosticBag diagnostics)
                 }
 
                 // The Section Header Table will be put just after all the sections
-                Layout.OffsetOfSectionHeaderTable = offset;
+                Layout.OffsetOfSectionHeaderTable = AlignHelper.AlignToUpper(offset, FileClass == ElfFileClass.Is32 ? 4u : 8u);
 
-                Layout.TotalSize = offset + (ulong)VisibleSectionCount * Layout.SizeOfSectionHeaderEntry;
+                Layout.TotalSize = Layout.OffsetOfSectionHeaderTable + (ulong)VisibleSectionCount * Layout.SizeOfSectionHeaderEntry;
             }
 
             // Update program headers with offsets from auto layout

src/LibObjectFile/Elf/ElfWriter{TEncoder}.cs

@@ -227,10 +227,16 @@ private void WriteSections()
         private void WriteSectionHeaderTable()
         {
             var offset = (ulong)Stream.Position - _startOfFile;
-            if (offset != Layout.OffsetOfSectionHeaderTable)
+            var diff = Layout.OffsetOfSectionHeaderTable - offset;
+            if (diff < 0 || diff > 8)
             {
                 throw new InvalidOperationException("Internal error. Unexpected offset for SectionHeaderTable");
             }
+            else if (diff != 0)
+            {
+                // Alignment
+                Stream.Write(stackalloc byte[(int)diff]);
+            }
 
             // Then write all regular sections
             var sections = ObjectFile.Sections;