[ELF] - Implemented -no-rosegment.

[grimar]

Summary

This is close to D26888, but implements only -no-rosegment flag.
This allows to reduce the changes.
So D26888 shows full version of functionality and can
be rebased if this one be landed.

[grimar]

• Addressed review comments.

lld/trunk/ELF/Config.h

struct Configuration {
   bool Nostdlib;
   bool OFormatBinary;
   bool Pic;
   bool Pie;
   bool PrintGcSections;
   bool Rela;
   bool Relocatable;
   bool SaveTemps;
+  bool SingleRoRx;
   bool Shared;
   bool Static = false;
   bool SysvHash = true;
   bool Target1Rel;
   bool Threads;
   bool Trace;
   bool Verbose;
   bool WarnCommon;

lld/trunk/ELF/Driver.cpp

case OPT_start_lib:
       InLib = true;
       break;
     case OPT_end_lib:
       InLib = false;
       break;
     }
   }
 
+  // -no-rosegment is used to avoid placing read only non-executable sections in
+  // their own segment. We do the same if SECTIONS command is present in linker
+  // script. See comment for computeFlags().
+  Config->SingleRoRx =
+      Args.hasArg(OPT_no_rosegment) || ScriptConfig->HasSections;
+
   if (Files.empty() && ErrorCount == 0)
     error("no input files");
 }
 
 // If -m <machine_type> was not given, infer it from object files.
 void LinkerDriver::inferMachineType() {
   if (Config->EKind != ELFNoneKind)
     return;

lld/trunk/ELF/Options.td

 def no_whole_archive: F<"no-whole-archive">,
   HelpText<"Restores the default behavior of loading archive members">;
 
 def noinhibit_exec: F<"noinhibit-exec">,
   HelpText<"Retain the executable output file whenever it is still usable">;
 
 def nopie: F<"nopie">, HelpText<"Do not create a position independent executable">;
 
+def no_rosegment: F<"no-rosegment">, HelpText<"Do not put read-only non-executable sections in their own segment">;
+
 def no_undefined: F<"no-undefined">,
   HelpText<"Report unresolved symbols even if the linker is creating a shared library">;
 
 def no_undefined_version: F<"no-undefined-version">,
   HelpText<"Report version scripts that refer undefined symbols">;
 
 def o: JoinedOrSeparate<["-"], "o">, MetaVarName<"<path>">,
   HelpText<"Path to file to write output">;

lld/trunk/ELF/Writer.cpp

 }
 
 // Linker scripts are responsible for aligning addresses. Unfortunately, most
 // linker scripts are designed for creating two PT_LOADs only, one RX and one
 // RW. This means that there is no alignment in the RO to RX transition and we
 // cannot create a PT_LOAD there.
 template <class ELFT>
 static typename ELFT::uint computeFlags(typename ELFT::uint F) {
-  if (ScriptConfig->HasSections && !(F & PF_W))
+  if (Config->SingleRoRx && !(F & PF_W))
     return F | PF_X;
   return F;
 }
 
 // Decide which program headers to create and which sections to include in each
 // one.
 template <class ELFT> std::vector<PhdrEntry<ELFT>> Writer<ELFT>::createPhdrs() {
   std::vector<Phdr> Ret;

lld/trunk/test/ELF/segments.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %t1
+# RUN: llvm-readobj --program-headers %t1 | FileCheck --check-prefix=ROSEGMENT %s
+
+# ROSEGMENT:      ProgramHeader {
+# ROSEGMENT:        Type: PT_LOAD
+# ROSEGMENT-NEXT:    Offset: 0x0
+# ROSEGMENT-NEXT:    VirtualAddress:
+# ROSEGMENT-NEXT:    PhysicalAddress:
+# ROSEGMENT-NEXT:    FileSize:
+# ROSEGMENT-NEXT:    MemSize:
+# ROSEGMENT-NEXT:    Flags [
+# ROSEGMENT-NEXT:      PF_R
+# ROSEGMENT-NEXT:    ]
+# ROSEGMENT-NEXT:    Alignment: 4096
+# ROSEGMENT-NEXT:  }
+# ROSEGMENT-NEXT:  ProgramHeader {
+# ROSEGMENT-NEXT:    Type: PT_LOAD
+# ROSEGMENT-NEXT:    Offset: 0x1000
+# ROSEGMENT-NEXT:    VirtualAddress:
+# ROSEGMENT-NEXT:    PhysicalAddress:
+# ROSEGMENT-NEXT:    FileSize:
+# ROSEGMENT-NEXT:    MemSize:
+# ROSEGMENT-NEXT:    Flags [
+# ROSEGMENT-NEXT:      PF_R
+# ROSEGMENT-NEXT:      PF_X
+# ROSEGMENT-NEXT:    ]
+# ROSEGMENT-NEXT:    Alignment: 4096
+# ROSEGMENT-NEXT:  }
+# ROSEGMENT-NEXT:  ProgramHeader {
+# ROSEGMENT-NEXT:    Type: PT_LOAD
+# ROSEGMENT-NEXT:    Offset: 0x2000
+# ROSEGMENT-NEXT:    VirtualAddress:
+# ROSEGMENT-NEXT:    PhysicalAddress:
+# ROSEGMENT-NEXT:    FileSize: 1
+# ROSEGMENT-NEXT:    MemSize: 1
+# ROSEGMENT-NEXT:    Flags [
+# ROSEGMENT-NEXT:      PF_R
+# ROSEGMENT-NEXT:      PF_W
+# ROSEGMENT-NEXT:    ]
+# ROSEGMENT-NEXT:    Alignment: 4096
+# ROSEGMENT-NEXT:  }
+
+# RUN: ld.lld -no-rosegment %t -o %t2
+# RUN: llvm-readobj --program-headers %t2 | FileCheck --check-prefix=NOROSEGMENT %s
+
+# NOROSEGMENT:     ProgramHeader {
+# NOROSEGMENT:       Type: PT_LOAD
+# NOROSEGMENT-NEXT:   Offset: 0x0
+# NOROSEGMENT-NEXT:   VirtualAddress:
+# NOROSEGMENT-NEXT:   PhysicalAddress:
+# NOROSEGMENT-NEXT:   FileSize:
+# NOROSEGMENT-NEXT:   MemSize:
+# NOROSEGMENT-NEXT:   Flags [
+# NOROSEGMENT-NEXT:     PF_R
+# NOROSEGMENT-NEXT:     PF_X
+# NOROSEGMENT-NEXT:   ]
+# NOROSEGMENT-NEXT:   Alignment: 4096
+# NOROSEGMENT-NEXT: }
+# NOROSEGMENT-NEXT: ProgramHeader {
+# NOROSEGMENT-NEXT:   Type: PT_LOAD
+# NOROSEGMENT-NEXT:   Offset: 0x1000
+# NOROSEGMENT-NEXT:   VirtualAddress:
+# NOROSEGMENT-NEXT:   PhysicalAddress:
+# NOROSEGMENT-NEXT:   FileSize:
+# NOROSEGMENT-NEXT:   MemSize:
+# NOROSEGMENT-NEXT:   Flags [
+# NOROSEGMENT-NEXT:     PF_R
+# NOROSEGMENT-NEXT:     PF_W
+# NOROSEGMENT-NEXT:   ]
+# NOROSEGMENT-NEXT:   Alignment: 4096
+# NOROSEGMENT-NEXT: }
+# NOROSEGMENT-NEXT: ProgramHeader {
+# NOROSEGMENT-NEXT:   Type: PT_GNU_STACK
+
+.global _start
+_start:
+ nop
+
+.section .ro,"a"
+nop
+
+.section .rw,"aw"
+nop
+
+.section .rx,"ax"
+nop