[ELF] Linkerscript: don't add program headers to segment when we have PHDRS directive but don't have FILEHDR and PHDRS attributes for segment

[evgeny777]

Summary

Linker shouldn't include program headers in PT_LOAD in the following case:

• PHDRS directive exists
• PT_LOAD segment doesn't contain PHDRS and/or FILEHDR attribute

Below is an example of such script:

PHDRS { 
  hdr PT_PHDR FILEHDR PHDRS;
  all PT_LOAD; 
}
SECTIONS { 
   . = 0x10000;
   .text : { *(.text) } : all
  /* other sections go here */
}

Current revision will detect that there is a place to put ELF and program headers and will do this even though 'all' segment doesn't
have PHDRS and FILEHDR attributes.

To make this patch as simple as possible, both FILEHDR and PHDRS attributes are required to put ELF and program headers to PT_LOAD.
GNU gold has the same requirement.

[• rafael]

LGTM

ELF/LinkerScript.cpp

else
       Sec->setVA(0);
   }
 
   uintX_t HeaderSize = getHeaderSize();
   auto FirstPTLoad =
       std::find_if(Phdrs.begin(), Phdrs.end(), [](const PhdrEntry<ELFT> &E) {
         return E.H.p_type == PT_LOAD;
       });
+
   if (HeaderSize <= MinVA && FirstPTLoad != Phdrs.end()) {
+    // If linker script specifies program headers and first PT_LOAD doesn't 
+    // both PHDRS and FILEHDR attributes then do nothing
+    if (!Opt.PhdrsCommands.empty()) {
+      size_t SegNum = std::distance(Phdrs.begin(), FirstPTLoad);
+      if (!Opt.PhdrsCommands[SegNum].HasPhdrs ||
+          !Opt.PhdrsCommands[SegNum].HasFilehdr)
+        return;
+    }
     // ELF and Program headers need to be right before the first section in
     // memory. Set their addresses accordingly.
     MinVA = alignDown(MinVA - HeaderSize, Target->PageSize);
     Out<ELFT>::ElfHeader->setVA(MinVA);
     Out<ELFT>::ProgramHeaders->setVA(Out<ELFT>::ElfHeader->getSize() + MinVA);
     FirstPTLoad->First = Out<ELFT>::ElfHeader;
     if (!FirstPTLoad->Last)
       FirstPTLoad->Last = Out<ELFT>::ProgramHeaders;

test/ELF/linkerscript/phdrs.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: echo "PHDRS {all PT_LOAD FILEHDR PHDRS ;} \
 # 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 that program headers are not written, unless we explicitly tell
+## lld to do this.
+# RUN: echo "PHDRS {all PT_LOAD;} \
+# RUN:       SECTIONS { \
+# RUN:           . = 0x10000200; \
+# RUN:           /DISCARD/ : {*(.text*)}  \
+# RUN:           .foo : {*(.foo.*)} :all \
+# RUN:       }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-readobj -program-headers %t1 | FileCheck --check-prefix=NOPHDR %s
+
 ## Check the AT(expr)
 # RUN: echo "PHDRS {all PT_LOAD FILEHDR PHDRS AT(0x500 + 0x500) ;} \
 # 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 --check-prefix=AT %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:    ]
 
+# NOPHDR:     ProgramHeaders [
+# NOPHDR-NEXT:  ProgramHeader {
+# NOPHDR-NEXT:    Type: PT_LOAD (0x1)
+# NOPHDR-NEXT:    Offset: 0x200
+# NOPHDR-NEXT:    VirtualAddress: 0x10000200
+# NOPHDR-NEXT:    PhysicalAddress: 0x10000200
+# NOPHDR-NEXT:    FileSize: 8
+# NOPHDR-NEXT:    MemSize: 8
+# NOPHDR-NEXT:    Flags [ (0x6)
+# NOPHDR-NEXT:      PF_R (0x4)
+# NOPHDR-NEXT:      PF_W (0x2)
+# NOPHDR-NEXT:    ]
+# NOPHDR-NEXT:    Alignment: 4096
+# NOPHDR-NEXT:  }
+# NOPHDR-NEXT: ]
+
 # AT:       ProgramHeaders [
 # AT-NEXT:    ProgramHeader {
 # AT-NEXT:      Type: PT_LOAD (0x1)
 # AT-NEXT:      Offset: 0x0
 # AT-NEXT:      VirtualAddress: 0x10000000
 # AT-NEXT:      PhysicalAddress: 0xA00
 # AT-NEXT:      FileSize: 521
 # AT-NEXT:      MemSize: 521