[lld] [llvm] [WebAssembly] Add segment NO_STRIP flag to support private retained data (PR #81539)

[Sam Clegg via llvm-commits]

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@@ -0,0 +1,62 @@
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj --triple=wasm32-unknown-unknown -o %t/main.o %t/main.s
+# RUN: llvm-mc -filetype=obj --triple=wasm32-unknown-unknown -o %t/liba_x.o %t/liba_x.s
+# RUN: llvm-mc -filetype=obj --triple=wasm32-unknown-unknown -o %t/liba_y.o %t/liba_y.s
+# RUN: rm -f %t/liba.a
+# RUN: llvm-ar rcs %t/liba.a %t/liba_x.o %t/liba_y.o
+# RUN: wasm-ld %t/main.o %t/liba.a --gc-sections -o %t/main.wasm --print-gc-sections | FileCheck %s --check-prefix=GC
+# RUN: obj2yaml %t/main.wasm | FileCheck %s
+
+# --gc-sections should remove non-retained and unused "weathers" section from live object liba_x.o
+# GC: removing unused section {{.*}}/liba.a(liba_x.o):(weathers)
+# Should not remove retained "greetings" sections from live objects main.o and liba_x.o
+# GC-NOT: removing unused section %t/main.o:(greetings)
+# GC-NOT: removing unused section %t/liba_x.o:(greetings)
+
+# Note: All symbols are private so that they don't join the symbol table.
+
+#--- main.s
+  .functype grab_liba () -> ()
+  .globl  _start
+_start:
+  .functype _start () -> ()
+  call grab_liba
+  end_function
+
+  .section greetings,"R",@
+  .asciz  "hello"
+  .section weathers,"R",@
+  .asciz  "cloudy"
+
+#--- liba_x.s
+  .globl  grab_liba
+grab_liba:
+  .functype grab_liba () -> ()
+  end_function
+
+  .section greetings,"R",@
+  .asciz  "world"
+  .section weathers,"",@
+  .asciz  "rainy"
+
+#--- liba_y.s
+        .section        greetings,"R",@
+        .asciz  "bye"
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sbc100 wrote:

Its kind of shame we can't do somekind hexdump of the resulting binary here and use `CHECK-NOT: bye` and `CHECK: world`..  I can't remember of llvm-objdump and do that yet?  @dschuff might know?

https://github.com/llvm/llvm-project/pull/81539