Propagate sh_entsize out

[• rafael]

Summary

No difference in practice other than having sh_entsize in the output.

This should simplify the patch for handling SHF_MERGE in -r.

[ruiu]

LGTM

ELF/SyntheticSections.cpp

2517

Can you reword this comment a bit? I mean, at first I thought this comment explained that the code have ignored Entsize which isn't true.

[grimar]

LGTM.

ELF/SyntheticSections.cpp

2521

In theory I believe there could be equal pieces when we merge string sections with different Entsize.
But that is probably too synthetic and unexpected case to care about.

2531

That is probably fine for this patch, but I find confusing that we emit SHF_MERGE flag and wrong EntSize to
regular output. Currently we select max entrysize when adding input sections to output section.
That does not make much sence I believe.

We probably might want to drop entry size and flag when doing non-relocatable link in followups.

[• espindola]

318306.

ELF/SyntheticSections.cpp

for (InputSectionBase *&S : InputSections) {
     // them instead of trying to merge.
     if (!MS->Live)
       continue;
 
     StringRef OutsecName = getOutputSectionName(MS->Name);
     uint32_t Alignment = std::max<uint32_t>(MS->Alignment, MS->Entsize);
 
     auto I = llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
+      // We could ignore Entsize in here: We would create a single Syncthetic
+      // section for two different values of Entsize. That would work, but no
+      // piece from one could be equal to a piece from the other.
+      // Using Entsize in here also allows us to propagate it to the synthetic
+      // section.
       return Sec->Name == OutsecName && Sec->Flags == MS->Flags &&
-             Sec->Alignment == Alignment;
+             Sec->Entsize == MS->Entsize && Sec->Alignment == Alignment;
     });
     if (I == MergeSections.end()) {
       MergeSyntheticSection *Syn =
           createMergeSynthetic(OutsecName, MS->Type, MS->Flags, Alignment);
       MergeSections.push_back(Syn);
       I = std::prev(MergeSections.end());
       S = Syn;
+      Syn->Entsize = MS->Entsize;
     } else {
       S = nullptr;
     }
     (*I)->addSection(MS);
   }
   for (auto *MS : MergeSections)
     MS->finalizeContents();
 

test/ELF/basic-aarch64.s

 # CHECK-NEXT:       SHF_STRINGS (0x20)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0
 # CHECK-NEXT:     Offset: 0x11000
 # CHECK-NEXT:     Size: 8
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:     EntrySize: 1
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 3
 # CHECK-NEXT:     Name: .symtab
 # CHECK-NEXT:     Type: SHT_SYMTAB (0x2)
 # CHECK-NEXT:     Flags [ (0x0)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0

test/ELF/basic-mips.s

 # CHECK-NEXT:       SHF_STRINGS (0x20)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0
 # CHECK-NEXT:     Offset: 0x20008
 # CHECK-NEXT:     Size: 8
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:     EntrySize: 1
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 8
 # CHECK-NEXT:     Name: .symtab
 # CHECK-NEXT:     Type: SHT_SYMTAB (0x2)
 # CHECK-NEXT:     Flags [ (0x0)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0

test/ELF/basic-ppc.s

 // CHECK-NEXT:       SHF_STRINGS (0x20)
 // CHECK-NEXT:     ]
 // CHECK-NEXT:     Address: 0x0
 // CHECK-NEXT:     Offset: 0x2030
 // CHECK-NEXT:     Size: 8
 // CHECK-NEXT:     Link: 0
 // CHECK-NEXT:     Info: 0
 // CHECK-NEXT:     AddressAlignment: 1
-// CHECK-NEXT:     EntrySize: 0
+// CHECK-NEXT:     EntrySize: 1
 // CHECK-NEXT:     SectionData (
 // CHECK-NEXT:       0000: 4C4C4420 312E3000 |LLD 1.0.|
 // CHECK-NEXT:     )
 // CHECK-NEXT:   }
 // CHECK-NEXT:   Section {
 // CHECK-NEXT:     Index: 7
 // CHECK-NEXT:     Name: .symtab
 // CHECK-NEXT:     Type: SHT_SYMTAB (0x2)

test/ELF/basic-sparcv9.s

 # CHECK-NEXT:       SHF_STRINGS (0x20)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0
 # CHECK-NEXT:     Offset: 0x102000
 # CHECK-NEXT:     Size: 8
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:     EntrySize: 1
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 3
 # CHECK-NEXT:     Name: .symtab
 # CHECK-NEXT:     Type: SHT_SYMTAB (0x2)
 # CHECK-NEXT:     Flags [ (0x0)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0

test/ELF/basic.s

 # CHECK-NEXT:       SHF_STRINGS (0x20)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0
 # CHECK-NEXT:     Offset: 0x2000
 # CHECK-NEXT:     Size: 8
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:     EntrySize: 1
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 3
 # CHECK-NEXT:     Name: .symtab
 # CHECK-NEXT:     Type: SHT_SYMTAB (0x2)
 # CHECK-NEXT:     Flags [ (0x0)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0

test/ELF/basic32.s

 # CHECK-NEXT:       SHF_STRINGS (0x20)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0
 # CHECK-NEXT:     Offset: 0x2000
 # CHECK-NEXT:     Size: 8
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:     EntrySize: 1
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 3
 # CHECK-NEXT:     Name: .symtab
 # CHECK-NEXT:     Type: SHT_SYMTAB
 # CHECK-NEXT:     Flags [
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0

test/ELF/basic64be.s

 # CHECK-NEXT:       SHF_STRINGS (0x20)
 # CHECK-NEXT:     ]
 # CHECK-NEXT:     Address: 0x0
 # CHECK-NEXT:     Offset: 0x30000
 # CHECK-NEXT:     Size: 8
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
-# CHECK-NEXT:     EntrySize: 0
+# CHECK-NEXT:     EntrySize: 1
 # CHECK-NEXT:     SectionData (
 # CHECK-NEXT:         0000: 4C4C4420 312E3000 |LLD 1.0.|
 # CHECK-NEXT:     )
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 7
 # CHECK-NEXT:     Name: .symtab
 # CHECK-NEXT:     Type: SHT_SYMTAB (0x2)

test/ELF/build-id.s

 # ALIGN-NEXT: Size:
 # ALIGN-NEXT: Link:
 # ALIGN-NEXT: Info:
 # ALIGN-NEXT: AddressAlignment: 4
 
 # DEFAULT:      Contents of section .note.test:
 # DEFAULT:      Contents of section .note.gnu.build-id:
 # DEFAULT-NEXT: 04000000 08000000 03000000 474e5500  ............GNU.
-# DEFAULT-NEXT: 1950bcad 6ffba153
+# DEFAULT-NEXT: 894c04e8 fbf5556b
 
 # MD5:      Contents of section .note.gnu.build-id:
 # MD5-NEXT: 04000000 10000000 03000000 474e5500  ............GNU.
-# MD5-NEXT: 6560b957 58afb40a 70f61d5a 7d76104e
+# MD5-NEXT: 6a51bbd7 9e8ee3f9 2e02d213 711cfec9
 
 # SHA1:      Contents of section .note.gnu.build-id:
 # SHA1-NEXT: 04000000 14000000 03000000 474e5500  ............GNU.
-# SHA1-NEXT: c41b2962 9fd0d863 0a35299a 746a626f
+# SHA1-NEXT: 9a8618b1 d6fd0e5c eda73dd8 76de5596
 
 # UUID:      Contents of section .note.gnu.build-id:
 # UUID-NEXT: 04000000 10000000 03000000 474e5500  ............GNU.
 
 # HEX:      Contents of section .note.gnu.build-id:
 # HEX-NEXT: 04000000 04000000 03000000 474e5500  ............GNU.
 # HEX-NEXT: 12345678
 
 # NONE-NOT: Contents of section .note.gnu.build-id:

test/ELF/compressed-debug-input.s

 # DATA-NEXT:     SHF_STRINGS (0x20)
 # DATA-NEXT:   ]
 # DATA-NEXT:   Address: 0x0
 # DATA-NEXT:   Offset: 0x1060
 # DATA-NEXT:   Size: 69
 # DATA-NEXT:   Link: 0
 # DATA-NEXT:   Info: 0
 # DATA-NEXT:   AddressAlignment: 1
-# DATA-NEXT:   EntrySize: 0
+# DATA-NEXT:   EntrySize: 1
 # DATA-NEXT:   SectionData (
 # DATA-NEXT:     0000: 6C6F6E67 20756E73 69676E65 6420696E  |long unsigned in|
 # DATA-NEXT:     0010: 7400756E 7369676E 65642063 68617200  |t.unsigned char.|
 # DATA-NEXT:     0020: 756E7369 676E6564 20696E74 00636861  |unsigned int.cha|
 # DATA-NEXT:     0030: 72007368 6F727420 756E7369 676E6564  |r.short unsigned|
 # DATA-NEXT:     0040: 20696E74 00                          | int.|
 # DATA-NEXT:   )
 # DATA-NEXT: }

test/ELF/gc-merge-local-sym.s

 // CHECK-NEXT:   SHF_STRINGS
 // CHECK-NEXT: ]
 // CHECK-NEXT: Address: 0x1C8
 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: 4
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 1
-// CHECK-NEXT: EntrySize: 0
+// CHECK-NEXT: EntrySize: 1
 // CHECK-NEXT: SectionData (
 // CHECK-NEXT:   0000: 61626300 |abc.|
 // CHECK-NEXT: )
 
 // CHECK:      Symbols [
 // CHECK:        Symbol {
 // CHECK-NOT:          Name: bar
 
         .global foo
 foo:
         leaq    .L.str(%rip), %rsi
         .section        .rodata.str1.1,"aMS",@progbits,1
 .L.str:
         .asciz  "abc"
 bar:
         .asciz  "def"

test/ELF/gc-sections-merge-addend.s

 // CHECK-NEXT:   SHF_STRINGS
 // CHECK-NEXT: ]
 // CHECK-NEXT: Address:
 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: 4
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 1
-// CHECK-NEXT: EntrySize: 0
+// CHECK-NEXT: EntrySize: 1
 // CHECK-NEXT: SectionData (
 // CHECK-NEXT:   0000: 62617200                    |bar.|
 // CHECK-NEXT: )
 
         .section        .data.f,"aw",@progbits
         .globl  f
 f:
         .quad .rodata.str1.1 + 4

test/ELF/gc-sections-merge-implicit-addend.s

 // CHECK-NEXT:   SHF_STRINGS
 // CHECK-NEXT: ]
 // CHECK-NEXT: Address:
 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: 4
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 1
-// CHECK-NEXT: EntrySize: 0
+// CHECK-NEXT: EntrySize: 1
 // CHECK-NEXT: SectionData (
 // CHECK-NEXT:   0000: 62617200                    |bar.|
 // CHECK-NEXT: )
 
         .section        .data.f,"aw",@progbits
         .globl  f
 f:
         .long .rodata.str1.1 + 4

test/ELF/gc-sections-merge.s

 // CHECK-NEXT:   SHF_STRINGS
 // CHECK-NEXT: ]
 // CHECK-NEXT: Address:
 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: 8
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 1
-// CHECK-NEXT: EntrySize: 0
+// CHECK-NEXT: EntrySize: 1
 // CHECK-NEXT: SectionData (
 // CHECK-NEXT:   0000: 666F6F00 62617200                    |foo.bar.|
 // CHECK-NEXT: )
 
 // GC:      Name: .rodata
 // GC-NEXT: Type: SHT_PROGBITS
 // GC-NEXT: Flags [
 // GC-NEXT:   SHF_ALLOC
 // GC-NEXT:   SHF_MERGE
 // GC-NEXT:   SHF_STRINGS
 // GC-NEXT: ]
 // GC-NEXT: Address:
 // GC-NEXT: Offset:
 // GC-NEXT: Size: 4
 // GC-NEXT: Link: 0
 // GC-NEXT: Info: 0
 // GC-NEXT: AddressAlignment: 1
-// GC-NEXT: EntrySize: 0
+// GC-NEXT: EntrySize: 1
 // GC-NEXT: SectionData (
 // GC-NEXT:   0000: 666F6F00                                |foo.|
 // GC-NEXT: )
 
         .section        .text.f,"ax",@progbits
         .globl  f
 f:
         leaq    .L.str(%rip), %rax

test/ELF/linkerscript/merge-sections.s

 # CHECK-NEXT:     SHF_STRINGS
 # CHECK-NEXT:   ]
 # CHECK-NEXT:   Address: 0x[[ADDR1:.*]]
 # CHECK-NEXT:   Offset: 0x[[ADDR1]]
 # CHECK-NEXT:   Size: 14
 # CHECK-NEXT:   Link: 0
 # CHECK-NEXT:   Info: 0
 # CHECK-NEXT:   AddressAlignment: 2
-# CHECK-NEXT:   EntrySize: 0
+# CHECK-NEXT:   EntrySize: 2
 # CHECK-NEXT: }
 
 # CHECK:      Name: begin
 # CHECK-NEXT: Value: 0x[[ADDR1]]
 
 # CHECK:      Name: end
 # 0x19E = begin + sizeof(.foo) = 0x190 + 0xE
 # CHECK-NEXT: Value: 0x19E

test/ELF/merge-string.s

 // CHECK-NEXT:   SHF_STRINGS
 // CHECK-NEXT: ]
 // CHECK-NEXT: Address:         0x1C8
 // CHECK-NEXT: Offset:  0x1C8
 // CHECK-NEXT: Size:    4
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 1
-// CHECK-NEXT: EntrySize: 0
+// CHECK-NEXT: EntrySize: 1
 // CHECK-NEXT: SectionData (
 // CHECK-NEXT:   0000: 61626300                             |abc.|
 // CHECK-NEXT: )
 
 // NOTAIL:      Name:    .rodata1
 // NOTAIL-NEXT: Type:    SHT_PROGBITS
 // NOTAIL-NEXT: Flags [
 // NOTAIL-NEXT:   SHF_ALLOC
 // NOTAIL-NEXT:   SHF_MERGE
 // NOTAIL-NEXT:   SHF_STRINGS
 // NOTAIL-NEXT: ]
 // NOTAIL-NEXT: Address:         0x1C8
 // NOTAIL-NEXT: Offset:  0x1C8
 // NOTAIL-NEXT: Size:    7
 // NOTAIL-NEXT: Link: 0
 // NOTAIL-NEXT: Info: 0
 // NOTAIL-NEXT: AddressAlignment: 1
-// NOTAIL-NEXT: EntrySize: 0
+// NOTAIL-NEXT: EntrySize: 1
 // NOTAIL-NEXT: SectionData (
 // NOTAIL-NEXT:   0000: 62630061 626300                     |bc.abc.|
 // NOTAIL-NEXT: )
 
 // NOMERGE:      Name:    .rodata1
 // NOMERGE-NEXT: Type:    SHT_PROGBITS
 // NOMERGE-NEXT: Flags [
 // NOMERGE-NEXT:   SHF_ALLOC

 // CHECK-NEXT:   SHF_STRINGS
 // CHECK-NEXT: ]
 // CHECK-NEXT: Address: 0x1CC
 // CHECK-NEXT: Offset: 0x1CC
 // CHECK-NEXT: Size: 4
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 2
-// CHECK-NEXT: EntrySize: 0
+// CHECK-NEXT: EntrySize: 2
 // CHECK-NEXT: SectionData (
 // CHECK-NEXT:   0000: 14000000                             |....|
 // CHECK-NEXT: )
 
 
 // CHECK:      Name:    bar
 // CHECK-NEXT: Value:   0x1C9
 
 // CHECK:      Name:    foo
 // CHECK-NEXT: Value:   0x1C8
 
 // CHECK:      Name: zed
 // CHECK-NEXT: Value: 0x1CC
 // CHECK-NEXT: Size: 0

test/ELF/merge.s

 // CHECK-NEXT:      SHF_MERGE
 // CHECK-NEXT:    ]
 // CHECK-NEXT:    Address: 0x200120
 // CHECK-NEXT:    Offset: 0x120
 // CHECK-NEXT:    Size: 8
 // CHECK-NEXT:    Link: 0
 // CHECK-NEXT:    Info: 0
 // CHECK-NEXT:    AddressAlignment: 4
-// CHECK-NEXT:    EntrySize: 0
+// CHECK-NEXT:    EntrySize: 4
 // CHECK-NEXT:    SectionData (
 // CHECK-NEXT:      0000: 10000000 42000000
 // CHECK-NEXT:    )
 
 
 // Address of the constant 0x10 = 0x200120 = 2097440
 // Address of the constant 0x42 = 0x200124 = 2097444