[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

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