[LLD][COFF] Merge .wowthk section to .text. (#76254)

.wowthk section is used by the compiler for ARM64EC entry thunks.

Author: cjacek

lld/COFF/Driver.cpp

@@ -1951,6 +1951,9 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   parseMerge(".00cfg=.rdata");
   parseMerge(".bss=.data");
 
+  if (isArm64EC(config->machine))
+    parseMerge(".wowthk=.text");
+
   if (config->mingw) {
     parseMerge(".ctors=.rdata");
     parseMerge(".dtors=.rdata");

lld/test/COFF/merge-wowthk.s

@@ -0,0 +1,44 @@
+// REQUIRES: aarch64
+
+// RUN: llvm-mc -filetype=obj -triple=arm64ec-windows %s -o %t-arm64ec.obj
+// RUN: llvm-mc -filetype=obj -triple=aarch64-windows %s -o %t-arm64.obj
+// RUN: llvm-mc -filetype=obj -triple=arm64ec-windows %S/Inputs/loadconfig-arm64ec.s -o %t-loadcfg.obj
+
+// Check that .wowthk section is merged into .text on ARM64EC target.
+
+// RUN: lld-link -out:%t.dll -machine:arm64ec %t-arm64ec.obj %t-loadcfg.obj -dll -noentry
+// RUN: llvm-objdump -d %t.dll | FileCheck  -check-prefix=DISASM %s
+// DISASM:      0000000180001000 <.text>:
+// DISASM-NEXT: 180001000: 52800040     mov     w0, #0x2                // =2
+// DISASM-NEXT: 180001004: d65f03c0     ret
+// DISASM-NEXT: 180001008: 52800060     mov     w0, #0x3                // =3
+// DISASM-NEXT: 18000100c: d65f03c0     ret
+
+// Check that .wowthk section is not merged on aarch64 target.
+
+// RUN: lld-link -out:%t.dll -machine:arm64 %t-arm64.obj -dll -noentry
+// RUN: llvm-objdump -d %t.dll | FileCheck -check-prefix=DISASM2 %s
+// DISASM2:      0000000180001000 <.text>:
+// DISASM2-NEXT: 180001000: 52800040     mov     w0, #0x2                // =2
+// DISASM2-NEXT: 180001004: d65f03c0     ret
+// DISASM2-EMPTY:
+// DISASM2-NEXT: Disassembly of section .wowthk:
+// DISASM2-EMPTY:
+// DISASM2-NEXT: 0000000180002000 <.wowthk>:
+// DISASM2-NEXT: 180002000: 52800060     mov     w0, #0x3                // =3
+// DISASM2-NEXT: 180002004: d65f03c0     ret
+
+
+        .text
+        .globl arm64ec_func_sym
+        .p2align 2, 0x0
+arm64ec_func_sym:
+        mov w0, #2
+        ret
+
+        .section .wowthk$aa, "x"
+        .globl wowthk_sym
+        .p2align 3, 0x0
+wowthk_sym:
+        mov w0, #3
+        ret