[mips] Removed the SHF_ALLOC flag from the .pdr section.

[s.egerton]

Summary

This section is used for debug information and has no need to be
in memory at runtime. With this patch, LLVM now emits the same flags as
the GNU assembler. This patch also fixes an error when compiling
the Linux kernel, The error is that there are relocations within the
.pdr section in a VDSO.

[dsanders]

LGTM with a couple tweaks to the commit message.

[mips] Made the .pdr section not allocatable.
This section is used for debug information and has no need to be
allocatable. This also causes errors when compiling the Linux kernel.

We should probably mention SHF_ALLOC on the first subject line.

Could you explain what kind of errors it fixes? It should be enough to mention eliminating relocations in a VDSO and that we now emit the same flags as GAS.

lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp

 }
 
 void MipsTargetELFStreamer::emitDirectiveEnd(StringRef Name) {
   MCAssembler &MCA = getStreamer().getAssembler();
   MCContext &Context = MCA.getContext();
   MCStreamer &OS = getStreamer();
 
   MCSectionELF *Sec = Context.getELFSection(".pdr", ELF::SHT_PROGBITS,
-                                            ELF::SHF_ALLOC | ELF::SHT_REL);
+                                            ELF::SHT_REL);
 
   MCSymbol *Sym = Context.getOrCreateSymbol(Name);
   const MCSymbolRefExpr *ExprRef =
       MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_None, Context);
 
   MCA.registerSection(*Sec);
   Sec->setAlignment(4);
 

test/MC/Mips/mips-pdr.s

 # ASMOUT:        .mask 0x10101010,-4
 # ASMOUT:        .fmask 0x01010101,-8
 # ASMOUT:        .end _local_foo
 # ASMOUT:        .size local_foo,
 
 # OBJOUT: Section {
 # OBJOUT:     Name: .pdr
 # OBJOUT:     Type: SHT_PROGBITS (0x1)
-# OBJOUT:     Flags [ (0xB)
-# OBJOUT:       SHF_ALLOC (0x2)
+# OBJOUT:     Flags [ (0x9)
+# OBJOUT-NOT:   SHF_ALLOC (0x2)
 # OBJOUT:       SHF_WRITE (0x1)
 # OBJOUT:     ]
 # OBJOUT:     Size: 64
 # OBJOUT:     SectionData (
 # OBJOUT:       0000: 00000000 10101010 FFFFFFFC 01010101
 # OBJOUT:       0010: FFFFFFF8 00000010 0000001E 0000001F
 # OBJOUT:       0020: 00000000 10101010 FFFFFFFC 01010101
 # OBJOUT:       0030: FFFFFFF8 00000010 0000001E 0000001F