[ELF] - Linkerscript: make section with no content to be SHT_PROGBITS by default.

[grimar]

Summary

Imagine next script:

SECTIONS { BYTE(0x11); }

Section content written to disk will be 0x11. Previous LLD behavior was to make this
section SHT_NOBITS. What is not correct because section has content.
ld.bfd makes such sections SHT_PROGBITS, this patch do the same.

This fixes PR32537

[ruiu]

LGTM

lld/trunk/ELF/LinkerScript.cpp

 }
 
 void LinkerScript::adjustSectionsBeforeSorting() {
   // If the output section contains only symbol assignments, create a
   // corresponding output section. The bfd linker seems to only create them if
   // '.' is assigned to, but creating these section should not have any bad
   // consequeces and gives us a section to put the symbol in.
   uint64_t Flags = SHF_ALLOC;
-  uint32_t Type = SHT_NOBITS;
+  uint32_t Type = SHT_PROGBITS;
   for (BaseCommand *Base : Opt.Commands) {
     auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
     if (!Cmd)
       continue;
     if (OutputSection *Sec = findSection(Cmd->Name, *OutputSections)) {
       Cmd->Sec = Sec;
       Flags = Sec->Flags;
       Type = Sec->Type;

lld/trunk/test/ELF/linkerscript/orphan-first-cmd.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 # RUN: echo "SECTIONS { \
 # RUN:         foo = 123; \
 # RUN:         . = 0x1000; \
 # RUN:         . = 0x2000; \
-# RUN:         .bar : { . = . + 1; } \
+# RUN:         .bar : { *(.bar) } \
 # RUN:       }" > %t.script
 # RUN: ld.lld -o %t -T %t.script %t.o -shared
 # RUN: llvm-readobj -s %t | FileCheck %s
 
 # CHECK:      Name: .text
 # CHECK-NEXT: Type: SHT_PROGBITS
 # CHECK-NEXT: Flags [
 # CHECK-NEXT:   SHF_ALLOC
 # CHECK-NEXT:   SHF_EXECINSTR
 # CHECK-NEXT: ]
 # CHECK-NEXT: Address: 0x1000
+
+.section .bar, "aw"

lld/trunk/test/ELF/linkerscript/symbol-only.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 
 # RUN: echo "SECTIONS { \
 # RUN:  . = SIZEOF_HEADERS; \
 # RUN:  abc : { foo = .; } \
 # RUN:  . = ALIGN(0x1000); \
 # RUN:  bar : { *(bar) } \
 # RUN: }" > %t.script
 # RUN: ld.lld -o %t1 --script %t.script %t -shared
 # RUN: llvm-objdump -section-headers -t %t1 | FileCheck %s
 # CHECK:      Sections:
 # CHECK-NEXT: Idx Name          Size      Address
 # CHECK-NEXT:   0               00000000 0000000000000000
-# CHECK:          abc           00000000 [[ADDR:[0-9a-f]*]] BSS
+# CHECK:          abc           00000000 [[ADDR:[0-9a-f]*]] DATA
 # CHECK-NEXT:     bar           00000000 0000000000001000 DATA
 
 # CHECK: SYMBOL TABLE:
 # CHECK:     [[ADDR]]         abc                00000000 foo
 
 .section bar, "a"