[lld][WebAssembly] Fix memory size in dylink section for -pie exectuables

This field to represents the amount of static data needed by
an dynamic library or executable it should not include things
like heap or stack areas, which in the case of `-pie` are
not determined until runtime (e.g. __stack_pointer is imported).

Differential Revision: https://reviews.llvm.org/D90261

Author: sbc100

lld/test/wasm/pie.ll

@@ -1,5 +1,5 @@
 ; RUN: llc -relocation-model=pic -mattr=+mutable-globals -filetype=obj %s -o %t.o
-; RUN: wasm-ld --no-gc-sections --allow-undefined -pie -o %t.wasm %t.o
+; RUN: wasm-ld --no-gc-sections --allow-undefined --experimental-pic -pie -o %t.wasm %t.o
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 target triple = "wasm32-unknown-emscripten"
@@ -30,6 +30,15 @@ define void @_start() {
   ret void
 }
 
+;      CHECK: Sections:
+; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     Name:            dylink
+; CHECK-NEXT:     MemorySize:      16
+; CHECK-NEXT:     MemoryAlignment: 2
+; CHECK-NEXT:     TableSize:       1
+; CHECK-NEXT:     TableAlignment:  0
+; CHECK-NEXT:     Needed:          []
+
 ; CHECK:        - Type:            IMPORT
 ; CHECK-NEXT:     Imports:
 ; CHECK-NEXT:       - Module:          env

lld/wasm/Writer.cpp

@@ -293,10 +293,10 @@ void Writer::layoutMemory() {
   if (WasmSym::dataEnd)
     WasmSym::dataEnd->setVirtualAddress(memoryPtr);
 
-  log("mem: static data = " + Twine(memoryPtr - dataStart));
-
-  if (config->shared) {
-    out.dylinkSec->memSize = memoryPtr;
+  uint64_t staticDataSize = memoryPtr - dataStart;
+  log("mem: static data = " + Twine(staticDataSize));
+  if (config->isPic) {
+    out.dylinkSec->memSize = staticDataSize;
     return;
   }
 
@@ -323,7 +323,6 @@ void Writer::layoutMemory() {
             Twine(maxMemorySetting));
     memoryPtr = config->initialMemory;
   }
-  out.dylinkSec->memSize = memoryPtr;
   out.memorySec->numMemoryPages =
       alignTo(memoryPtr, WasmPageSize) / WasmPageSize;
   log("mem: total pages = " + Twine(out.memorySec->numMemoryPages));