[WebAssembly] Use GeneralDynamic TLS for exception handling builtins.

[sbc100]

Summary

These global TLS symbols are shared across all shared libraries and
cannot be assumed to be local to the currently module.

Also add new error in the linker when TLS relocations are used against
undefined symbols. TLS relocations are offsets into the current modules
tls data segment, and don't make sense for undefined symbols which are
modeled as global imports.

Fixes: https://github.com/emscripten-core/emscripten/issues/13398

[sbc100]

• add lld error

[sbc100]

• rebase

[aheejin]

These global TLS symbols are shared across all shared libraries and cannot be assumed to be local to the currently module.

Is there any other libraries other than compiler-rt with which these variables are shared?

Fixes: https://github.com/emscripten-core/emscripten/issues/1339

I think the link is incorrect? That issue is from 2013.

[sbc100]

In D119630#3320208, @aheejin wrote:

These global TLS symbols are shared across all shared libraries and cannot be assumed to be local to the currently module.

Is there any other libraries other than compiler-rt with which these variables are shared?

No, as afar as I know system/lib/compiler-rt/emscripten_exception_builtins.c is the only place these get defined or used aside from in this code here.

Fixes: https://github.com/emscripten-core/emscripten/issues/1339

I think the link is incorrect? That issue is from 2013.

Oops I was missing an 8: https://github.com/emscripten-core/emscripten/issues/13398

lld/test/wasm/relocation-bad-tls.s

 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
 # RUN: not wasm-ld --shared-memory %t.o -o %t.wasm 2>&1 | FileCheck %s
 
 .globl _start
 _start:
   .functype _start () -> ()
   i32.const foo@TLSREL
   i32.const bar@TLSREL
+  i32.const baz@TLSREL
+  drop
   drop
   drop
   end_function
 
 .section  .data,"",@
 .globl  foo
 foo:
   .int32  0
   .size foo, 4
 
 .section  .bss,"",@
 .globl  bar
 bar:
   .int32  0
   .size bar, 4
 
 # CHECK: relocation R_WASM_MEMORY_ADDR_TLS_SLEB cannot be used against `foo` in non-TLS section: .data
 # CHECK: relocation R_WASM_MEMORY_ADDR_TLS_SLEB cannot be used against `bar` in non-TLS section: .bss
+# CHECK: relocation R_WASM_MEMORY_ADDR_TLS_SLEB cannot be used against an undefined symbol `baz`

lld/wasm/Relocations.cpp

case R_WASM_TABLE_INDEX_REL_SLEB64:
       break;
     case R_WASM_GLOBAL_INDEX_LEB:
     case R_WASM_GLOBAL_INDEX_I32:
       if (!isa<GlobalSymbol>(sym))
         addGOTEntry(sym);
       break;
     case R_WASM_MEMORY_ADDR_TLS_SLEB:
     case R_WASM_MEMORY_ADDR_TLS_SLEB64:
+      if (!sym->isDefined()) {
+        error(toString(file) + ": relocation " + relocTypeToString(reloc.Type) +
+              " cannot be used against an undefined symbol `" + toString(*sym) +
+              "`");
+      }
       // In single-threaded builds TLS is lowered away and TLS data can be
       // merged with normal data and allowing TLS relocation in non-TLS
       // segments.
       if (config->sharedMemory) {
         if (!sym->isTLS()) {
           error(toString(file) + ": relocation " +
                 relocTypeToString(reloc.Type) +
                 " cannot be used against non-TLS symbol `" + toString(*sym) +

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

static GlobalVariable *getGlobalVariable(Module &M, Type *Ty,
 
   // If the target supports TLS, make this variable thread-local. We can't just
   // unconditionally make it thread-local and depend on
   // CoalesceFeaturesAndStripAtomics to downgrade it, because stripping TLS has
   // the side effect of disallowing the object from being linked into a
   // shared-memory module, which we don't want to be responsible for.
   auto *Subtarget = TM.getSubtargetImpl();
   auto TLS = Subtarget->hasAtomics() && Subtarget->hasBulkMemory()
-                 ? GlobalValue::LocalExecTLSModel
+                 ? GlobalValue::GeneralDynamicTLSModel
                  : GlobalValue::NotThreadLocal;
   GV->setThreadLocalMode(TLS);
   return GV;
 }
 
 // Simple function name mangler.
 // This function simply takes LLVM's string representation of parameter types
 // and concatenate them with '_'. There are non-alphanumeric characters but llc

llvm/test/CodeGen/WebAssembly/lower-em-exceptions.ll

 ; RUN: opt < %s -wasm-lower-em-ehsjlj -enable-emscripten-cxx-exceptions -S | FileCheck %s --check-prefixes=CHECK,NO-TLS -DPTR=i32
 ; RUN: opt < %s -wasm-lower-em-ehsjlj -enable-emscripten-cxx-exceptions -S --mattr=+atomics,+bulk-memory | FileCheck %s --check-prefixes=CHECK,TLS -DPTR=i32
 ; RUN: opt < %s -wasm-lower-em-ehsjlj -enable-emscripten-cxx-exceptions --mtriple=wasm64-unknown-unknown -data-layout="e-m:e-p:64:64-i64:64-n32:64-S128" -S | FileCheck %s --check-prefixes=CHECK -DPTR=i64
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 @_ZTIi = external constant i8*
 @_ZTIc = external constant i8*
 ; NO-TLS-DAG: __THREW__ = external global [[PTR]]
 ; NO-TLS-DAG: __threwValue = external global i32
-; TLS-DAG: __THREW__ = external thread_local(localexec) global [[PTR]]
-; TLS-DAG: __threwValue = external thread_local(localexec) global i32
+; TLS-DAG: __THREW__ = external thread_local global [[PTR]]
+; TLS-DAG: __threwValue = external thread_local global i32
 
 ; Test invoke instruction with clauses (try-catch block)
 define void @clause() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
 ; CHECK-LABEL: @clause(
 entry:
   invoke void @foo(i32 3)
           to label %invoke.cont unwind label %lpad
 ; CHECK: entry:

llvm/test/CodeGen/WebAssembly/lower-em-sjlj.ll

 ; RUN: opt < %s -wasm-lower-em-ehsjlj -enable-emscripten-sjlj -S | FileCheck %s --check-prefixes=CHECK,NO-TLS -DPTR=i32
 ; RUN: opt < %s -wasm-lower-em-ehsjlj -enable-emscripten-sjlj -S --mattr=+atomics,+bulk-memory | FileCheck %s --check-prefixes=CHECK,TLS -DPTR=i32
 ; RUN: opt < %s -wasm-lower-em-ehsjlj -enable-emscripten-sjlj --mtriple=wasm64-unknown-unknown -data-layout="e-m:e-p:64:64-i64:64-n32:64-S128" -S | FileCheck %s --check-prefixes=CHECK -DPTR=i64
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 %struct.__jmp_buf_tag = type { [6 x i32], i32, [32 x i32] }
 
 @global_var = global i32 0, align 4
 ; NO-TLS-DAG: __THREW__ = external global [[PTR]]
 ; NO-TLS-DAG: __threwValue = external global [[PTR]]
-; TLS-DAG: __THREW__ = external thread_local(localexec) global i32
-; TLS-DAG: __threwValue = external thread_local(localexec) global i32
+; TLS-DAG: __THREW__ = external thread_local global i32
+; TLS-DAG: __threwValue = external thread_local global i32
 @global_longjmp_ptr = global void (%struct.__jmp_buf_tag*, i32)* @longjmp, align 4
 ; CHECK-DAG: @global_longjmp_ptr = global void (%struct.__jmp_buf_tag*, i32)* bitcast (void ([[PTR]], i32)* @emscripten_longjmp to void (%struct.__jmp_buf_tag*, i32)*)
 
 ; Test a simple setjmp - longjmp sequence
 define void @setjmp_longjmp() {
 ; CHECK-LABEL: @setjmp_longjmp
 entry:
   %buf = alloca [1 x %struct.__jmp_buf_tag], align 16