[LLD] [COFF] Merge the .ctors, .dtors and .CRT sections into .rdata for MinGW

[mstorsjo]

Summary

There's no point in keeping them as separate sections.

This differs from GNU ld, which places .ctors and .dtors content in .text (implemented by a built-in linker script). But since the content only is pointers, there's no need to have it executable.

GNU ld also leaves .CRT separate as its own standalone section.

[mstorsjo]

On the same topic; GNU ld doesn't merge .CRT into .rdata either, but perhaps we should? (It shouldn't hurt.) For MSVC environments, afaik this is handled by an embedded directive /merge:.CRT=.rdata from msvcrt.lib.

[rnk]

lgtm

COFF/Driver.cpp

   // Add default section merging rules after user rules. User rules take
   // precedence, but we will emit a warning if there is a conflict.
   parseMerge(".idata=.rdata");
   parseMerge(".didat=.rdata");
   parseMerge(".edata=.rdata");
   parseMerge(".xdata=.rdata");
   parseMerge(".bss=.data");
 
+  if (Config->MinGW) {
+    parseMerge(".ctors=.rdata");
+    parseMerge(".dtors=.rdata");
+    parseMerge(".CRT=.rdata");
+  }
+
   // Handle /section
   for (auto *Arg : Args.filtered(OPT_section))
     parseSection(Arg->getValue());
 
   // Handle /aligncomm
   for (auto *Arg : Args.filtered(OPT_aligncomm))
     parseAligncomm(Arg->getValue());
 

test/COFF/ctors_dtors_priority.s

 # REQUIRES: x86
 # RUN: llvm-mc -triple=x86_64-windows-gnu -filetype=obj -o %t.obj %s
-# RUN: lld-link -entry:main %t.obj -out:%t.exe
+# RUN: lld-link -lldmingw -entry:main %t.obj -out:%t.exe
 # RUN: llvm-objdump -s %t.exe | FileCheck %s
 
 .globl main
 main:
   nop
 
 .section .ctors.00005, "w"
   .quad 2
 .section .ctors, "w"
   .quad 1
 .section .ctors.00100, "w"
   .quad 3
 
 .section .dtors, "w"
-  .quad 1
+  .quad 4
 .section .dtors.00100, "w"
-  .quad 3
+  .quad 6
 .section .dtors.00005, "w"
-  .quad 2
+  .quad 5
+
+# Also test that the .CRT section is merged into .rdata
+
+.section .CRT$XCA, "dw"
+  .quad 7
+  .quad 8
 
-# CHECK:      Contents of section .ctors:
-# CHECK-NEXT: 140002000 01000000 00000000 02000000 00000000
-# CHECK-NEXT: 140002010 03000000 00000000
-
-# CHECK:      Contents of section .dtors:
-# CHECK-NEXT: 140003000 01000000 00000000 02000000 00000000
-# CHECK-NEXT: 140003010 03000000 00000000
+# CHECK:      Contents of section .rdata:
+# CHECK-NEXT: 140002000 07000000 00000000 08000000 00000000
+# CHECK-NEXT: 140002010 01000000 00000000 02000000 00000000
+# CHECK-NEXT: 140002020 03000000 00000000 04000000 00000000
+# CHECK-NEXT: 140002030 05000000 00000000 06000000 00000000