[ELF] Support FLAGS attribute in PHDR definition

[evgeny777]

Summary

Allows user to specify flags for each program header

[ruiu]

ELF/LinkerScript.cpp

620

Set Flags to PF_R by default. Then you should be able to remove HasFlags member.

[evgeny777]

ELF/LinkerScript.cpp

620

I have small concern about such change. Currently if we don't set PHDR flags in script then flags are OR-combined from member section flags. If we set flags in script then I guess we can't change them while assigning sections to segment, can we?

[ruiu]

ELF/LinkerScript.cpp

620

I see. Then how about setting to -1 if a flag is absent?

[evgeny777]

Review updated

[ruiu]

LGTM

[grimar]

ELF/LinkerScript.cpp

341–342

Is this correct ?

[evgeny777]

ELF/LinkerScript.cpp

341–342

That's definitely a bug. Thanks, George!

[grimar]

ELF/LinkerScript.cpp

341–342

Please update testcase to catch this then.

ELF/LinkerScript.h

struct SectionsCommand {
   std::vector<StringRef> Phdrs;
 };
 
 struct PhdrsCommand {
   StringRef Name;
   unsigned Type;
   bool HasFilehdr;
   bool HasPhdrs;
+  bool HasFlags;
+  unsigned Flags;
 };
 
 // ScriptConfiguration holds linker script parse results.
 struct ScriptConfiguration {
   // SECTIONS commands.
   std::vector<SectionRule> Sections;
 
   // Section fill attribute for each section.

ELF/LinkerScript.cpp

LinkerScript<ELFT>::createPhdrs(ArrayRef<OutputSectionBase<ELFT> *> Sections) {
   int TlsNum = -1;
   int NoteNum = -1;
   int RelroNum = -1;
   Phdr *Load = nullptr;
   uintX_t Flags = PF_R;
   std::vector<Phdr> Phdrs;
 
   for (const PhdrsCommand &Cmd : Opt.PhdrsCommands) {
-    Phdrs.emplace_back(Cmd.Type, PF_R);
+    Phdrs.emplace_back(Cmd.Type, Cmd.HasFlags ? Cmd.Flags : PF_R);
     Phdr &Added = Phdrs.back();
 
     if (Cmd.HasFilehdr)
       Added.AddSec(Out<ELFT>::ElfHeader);
     if (Cmd.HasPhdrs)
       Added.AddSec(Out<ELFT>::ProgramHeaders);
 
     switch (Cmd.Type) {
if (!needsPtLoad<ELFT>(Sec))
       continue;
 
     const std::vector<size_t> &PhdrIds =
         getPhdrIndicesForSection(Sec->getName());
     if (!PhdrIds.empty()) {
       // Assign headers specified by linker script
       for (size_t Id : PhdrIds) {
         Phdrs[Id].AddSec(Sec);
+        if (!Opt.PhdrsCommands[Id].HasFlags)
           Phdrs[Id].H.p_flags |= toPhdrFlags(Sec->getFlags());
       }
     } else {
       // If we have no load segment or flags've changed then we want new load
       // segment.
       uintX_t NewFlags = toPhdrFlags(Sec->getFlags());
       if (Load == nullptr || Flags != NewFlags) {
         Load = &*Phdrs.emplace(Phdrs.end(), PT_LOAD, NewFlags);
         Flags = NewFlags;
void ScriptParser::readOutputFormat() {
   next();
   expect(")");
 }
 
 void ScriptParser::readPhdrs() {
   expect("{");
   while (!Error && !skip("}")) {
     StringRef Tok = next();
-    Opt.PhdrsCommands.push_back({Tok, PT_NULL, false, false});
+    Opt.PhdrsCommands.push_back({Tok, PT_NULL, false, false, false, 0});
     PhdrsCommand &PhdrCmd = Opt.PhdrsCommands.back();
 
     PhdrCmd.Type = readPhdrType();
     do {
       Tok = next();
       if (Tok == ";")
         break;
       if (Tok == "FILEHDR")
         PhdrCmd.HasFilehdr = true;
       else if (Tok == "PHDRS")
         PhdrCmd.HasPhdrs = true;
+      else if (Tok == "FLAGS") {
+        PhdrCmd.HasFlags = true;
+        expect("(");
+        next().getAsInteger(0, PhdrCmd.Flags);
+        expect(")"); 
+      }
       else
         setError("unexpected header attribute: " + Tok);
     } while (!Error);
   }
 }
 
 void ScriptParser::readSearchDir() {
   expect("(");

test/ELF/linkerscript-phdrs-flags.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "PHDRS {all PT_LOAD FILEHDR PHDRS FLAGS (7);} \
+# RUN:       SECTIONS { \
+# RUN:           . = 0x10000200; \
+# RUN:           .text : {*(.text.*)} :all \
+# RUN:           .foo : {*(.foo.*)} :all \
+# RUN:           .data : {*(.data.*)} :all}" > %t.script
+
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-readobj -program-headers %t1 | FileCheck %s
+# CHECK:     ProgramHeaders [
+# CHECK-NEXT:  ProgramHeader {
+# CHECK-NEXT:    Type: PT_LOAD (0x1)
+# CHECK-NEXT:    Offset: 0x0
+# CHECK-NEXT:    VirtualAddress: 0x10000000
+# CHECK-NEXT:    PhysicalAddress: 0x10000000
+# CHECK-NEXT:    FileSize: 521
+# CHECK-NEXT:    MemSize: 521
+# CHECK-NEXT:    Flags [ (0x7)
+# CHECK-NEXT:      PF_R (0x4)
+# CHECK-NEXT:      PF_W (0x2)
+# CHECK-NEXT:      PF_X (0x1)
+# CHECK-NEXT:    ]
+
+.global _start
+_start:
+ nop
+
+.section .foo.1,"a"
+foo1:
+ .long 0
+
+.section .foo.2,"a"
+foo2:
+ .long 0