[ELF] Fix bugzilla #38748 for option no-rosegment

[NickHung]

Summary

Fix option no-rosegment for bugzilla #38784

* Prior to this revision, lld always groups read-only sections into
executable segments. This decision might cause a huge executable size as
described in the bugzilla.
* This revision tries to group the following sections with the current
segment if no-rosegment is on.

* add a new test case: no-rosegment.s
* modify 4 test cases accordingly.

[smeenai]

You'll wanna upload the patch with full context (http://llvm.org/docs/Phabricator.html).

[MaskRay]

I made a comment in https://bugs.llvm.org/show_bug.cgi?id=38784

For your example, it is ld.bfd which creates a 2.1M executable, not lld

ELF/Writer.cpp

     return PF_R | PF_W | PF_X;
   if (Config->ExecuteOnly && (Flags & PF_X))
     return Flags & ~PF_R;
-  if (Config->SingleRoRx && !(Flags & PF_W))
-    return Flags | PF_X;
   return Flags;
 }
 

   Load->add(Out::ElfHeader);
   Load->add(Out::ProgramHeaders);
 
+  auto isRO = [](uint64_t Flags) {
+    return ((Flags & PF_X) || (Flags & PF_W)) ? false : true;
+  };
+
   for (OutputSection *Sec : OutputSections) {
     if (!(Sec->Flags & SHF_ALLOC))
       break;

     if (((Sec->LMAExpr ||
           (Sec->LMARegion && (Sec->LMARegion != Load->FirstSec->LMARegion))) &&
          Load->LastSec != Out::ProgramHeaders) ||
-        Sec->MemRegion != Load->FirstSec->MemRegion || Flags != NewFlags) {
-
+        Sec->MemRegion != Load->FirstSec->MemRegion) {
       Load = AddHdr(PT_LOAD, NewFlags);
-      Flags = NewFlags;
+    } else if ((Load->p_flags != NewFlags)) {
+      if (Config->SingleRoRx && isRO(Load->p_flags))
+        Load->p_flags = NewFlags;
+      else
+        Load = AddHdr(PT_LOAD, NewFlags);
     }
-
     Load->add(Sec);
   }
 

test/ELF/linkerscript/at-self-reference.s

 # CHECK-NEXT:    PhysicalAddress: 0x1000
 # CHECK-NEXT:    FileSize: 3
 # CHECK-NEXT:    MemSize: 3
-# CHECK-NEXT:    Flags [ (0x5)
+# CHECK-NEXT:    Flags [ (0x4)
 # CHECK-NEXT:      PF_R (0x4)
-# CHECK-NEXT:      PF_X (0x1)
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Alignment: 4096
 # CHECK-NEXT:  }

test/ELF/linkerscript/at.s

 # CHECK-NEXT:     MemSize: 16
 # CHECK-NEXT:     Flags [
 # CHECK-NEXT:       PF_R
-# CHECK-NEXT:       PF_X
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Alignment:
 # CHECK-NEXT:   }

 # CHECK-NEXT:     MemSize: 8
 # CHECK-NEXT:     Flags [
 # CHECK-NEXT:       PF_R
-# CHECK-NEXT:       PF_X
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Alignment: 4096
 # CHECK-NEXT:   }

 # CHECK-NEXT:     MemSize: 8
 # CHECK-NEXT:     Flags [
 # CHECK-NEXT:       PF_R
-# CHECK-NEXT:       PF_X
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Alignment: 4096
 # CHECK-NEXT:   }

test/ELF/linkerscript/overlay.test

 
 # CHECK:      Program Headers:
 # CHECK:      Type Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
-# CHECK-NEXT: LOAD 0x001000 0x0000000000001000 0x0000000000004000 0x000008 0x000008 R E 0x1000
+# CHECK-NEXT: LOAD 0x001000 0x0000000000001000 0x0000000000004000 0x000008 0x000008 R  0x1000
 # CHECK-NEXT: LOAD 0x002000 0x0000000000001000 0x0000000000004008 0x000009 0x000009 R E 0x1000

test/ELF/no-rosegment.s

+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: echo "SECTIONS { \
+# RUN: .text : { *(.text) } \
+# RUN: . = 0x200000;  \
+# RUN: .rodata : { *(.rodata) } \
+# RUN: }" > %t.script
+# RUN: ld.lld --no-rosegment -o %t -T %t.script %t.o
+# RUN: llvm-readelf -l %t | FileCheck %s
+
+.text
+nop
+.rodata
+        .word 0x41
+        .word 0x42
+        .word 0x43
+        .word 0x44
+#CHECK: LOAD           0x001000 0x0000000000000000 0x0000000000000000 0x000001 0x000001 R E 0x1000
+#CHECK-NEXT: LOAD           0x002000 0x0000000000200000 0x0000000000200000 0x000008 0x000008 R   0x1000

test/ELF/phdr-align.s

 # CHECK-NEXT:      SHF_ALLOC
 # CHECK-NEXT:      SHF_WRITE
 # CHECK-NEXT:    ]
-# CHECK-NEXT:    Address: 0x158
-# CHECK-NEXT:    Offset: 0x158
+# CHECK-NEXT:    Address: 0x120
+# CHECK-NEXT:    Offset: 0x120
 # CHECK-NEXT:    Size: 6
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0

 # CHECK-NEXT:      SHF_ALLOC
 # CHECK-NEXT:      SHF_WRITE
 # CHECK-NEXT:    ]
-# CHECK-NEXT:    Address: 0x15E
-# CHECK-NEXT:    Offset: 0x15E
+# CHECK-NEXT:    Address: 0x126
+# CHECK-NEXT:    Offset: 0x126
 # CHECK-NEXT:    Size: 2
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0

 # CHECK-NEXT:      SHF_ALLOC
 # CHECK-NEXT:      SHF_EXECINSTR
 # CHECK-NEXT:    ]
-# CHECK-NEXT:    Address: 0x160
-# CHECK-NEXT:    Offset: 0x160
+# CHECK-NEXT:    Address: 0x128
+# CHECK-NEXT:    Offset: 0x128
 # CHECK-NEXT:    Size: 1
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0