[llvm-size] Output REL, RELA and STRTAB sections when allocatable

gnu size has a number of special cases regarding REL, RELA and STRTAB
sections being considered in size output. To avoid unnecessary
complexity this commit makes llvm size outputs these sections in cases
they have the SHF_ALLOC flag.

Differential Revision: https://reviews.llvm.org/D82479

llvm/test/tools/llvm-size/output-alloc.test

@@ -0,0 +1,38 @@
+## gnu size has a number of special cases regarding REL, RELA and STRTAB sections being considered in size output. 
+## To avoid unnecessary complexity llvm size outputs these sections in cases they have the SHF_ALLOC flag.
+
+# RUN: yaml2obj %s -o %t1
+# RUN: llvm-size --format=sysv %t1 | FileCheck %s
+
+# CHECK:      section     size   addr
+# CHECK-NEXT: .rela.alloc
+# CHECK-NEXT: .rel.alloc
+# CHECK-NEXT: .strtab.alloc
+# CHECK-NEXT: Total
+# CHECK-EMPTY:
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:  .rela.alloc
+    Type:  SHT_RELA
+    Flags: [ SHF_ALLOC ]
+  - Name:  .rel.alloc
+    Type:  SHT_REL
+    Flags: [ SHF_ALLOC ]
+  - Name:  .strtab.alloc
+    Type:  SHT_STRTAB
+    Flags: [ SHF_ALLOC ]
+  - Name:  .rela
+    Type:  SHT_RELA
+    Flags: []
+  - Name:  .rel
+    Type:  SHT_REL
+    Flags: []
+  - Name:  .strtab
+    Type:  SHT_STRTAB
+    Flags: []

llvm/tools/llvm-size/llvm-size.cpp

@@ -187,10 +187,11 @@ static bool considerForSize(ObjectFile *Obj, SectionRef Section) {
   switch (static_cast<ELFSectionRef>(Section).getType()) {
   case ELF::SHT_NULL:
   case ELF::SHT_SYMTAB:
+    return false;
   case ELF::SHT_STRTAB:
   case ELF::SHT_REL:
   case ELF::SHT_RELA:
-    return false;
+    return static_cast<ELFSectionRef>(Section).getFlags() & ELF::SHF_ALLOC;
   }
   return true;
 }