[WebAssembly] Allow import and export of TLS symbols between DSOs

We previously had a limitation that TLS variables could not
be exported (and therefore could also not be imported).  This
change removed that limitation.

Differential Revision: https://reviews.llvm.org/D108877

Author: sbc100

lld/test/wasm/pie.ll

@@ -91,7 +91,7 @@ declare void @external_func()
 ; RUN: obj2yaml %t.shmem.wasm | FileCheck %s --check-prefix=SHMEM
 
 ; SHMEM:         - Type:            CODE
-; SHMEM:           - Index:           6
+; SHMEM:           - Index:           7
 ; SHMEM-NEXT:        Locals:          []
 ; SHMEM-NEXT:        Body:            100310050B
 
@@ -109,11 +109,13 @@ declare void @external_func()
 ; SHMEM-NEXT:      - Index:           5
 ; SHMEM-NEXT:        Name:            __wasm_apply_global_relocs
 ; SHMEM-NEXT:      - Index:           6
-; SHMEM-NEXT:        Name:            __wasm_start
+; SHMEM-NEXT:        Name:            __wasm_apply_global_tls_relocs
 ; SHMEM-NEXT:      - Index:           7
-; SHMEM-NEXT:        Name:            foo
+; SHMEM-NEXT:        Name:            __wasm_start
 ; SHMEM-NEXT:      - Index:           8
-; SHMEM-NEXT:        Name:            get_data_address
+; SHMEM-NEXT:        Name:            foo
 ; SHMEM-NEXT:      - Index:           9
+; SHMEM-NEXT:        Name:            get_data_address
+; SHMEM-NEXT:      - Index:           10
 ; SHMEM-NEXT:        Name:            _start
 

lld/test/wasm/shared-needed.s

@@ -29,6 +29,7 @@ data:
 # SO1-NEXT:     TableSize:       0
 # SO1-NEXT:     TableAlignment:  0
 # SO1-NEXT:     Needed:          []
+# SO1-NEXT:     ExportInfo:      []
 # SO1-NEXT:   - Type:            TYPE
 
 # SO2:      Sections:
@@ -40,4 +41,5 @@ data:
 # SO2-NEXT:     TableAlignment:  0
 # SO2-NEXT:     Needed:
 # SO2-NEXT:       - shared-needed.s.tmp1.so
+# SO2-NEXT:     ExportInfo:      []
 # SO2-NEXT:   - Type:            TYPE

lld/test/wasm/shared.s

@@ -133,6 +133,7 @@ get_local_func_address:
 # CHECK-NEXT:     TableSize:       2
 # CHECK-NEXT:     TableAlignment:  0
 # CHECK-NEXT:     Needed:          []
+# CHECK-NEXT:     ExportInfo:      []
 # CHECK-NEXT:   - Type:            TYPE
 
 # check for import of __table_base and __memory_base globals

lld/test/wasm/shared64.s

@@ -134,6 +134,7 @@ get_local_func_address:
 # CHECK-NEXT:     TableSize:       2
 # CHECK-NEXT:     TableAlignment:  0
 # CHECK-NEXT:     Needed:          []
+# CHECK-NEXT:     ExportInfo:      []
 # CHECK-NEXT:   - Type:            TYPE
 
 # check for import of __table_base and __memory_base globals

lld/test/wasm/tls-export.s

@@ -1,10 +1,6 @@
 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
-# RUN: wasm-ld -no-gc-sections --shared-memory --no-entry -o %t.wasm %t.o
-# RUN: not wasm-ld --shared-memory --no-entry --export=tls1 -o %t.wasm %t.o 2>&1 | FileCheck %s
-# With --export-all we ignore TLS symbols so we don't expect an error here
-# RUN: wasm-ld --shared-memory --no-entry --export-all -o %t.wasm %t.o
-
-# CHECK: error: TLS symbols cannot yet be exported: `tls1`
+# RUN: wasm-ld -shared --experimental-pic -o %t.so %t.o
+# RUN: obj2yaml %t.so | FileCheck %s
 
 .section  .tdata.tls1,"",@
 .globl  tls1
@@ -24,3 +20,26 @@ tls1:
   .int8 43
   .int8 15
   .ascii "mutable-globals"
+
+#      CHECK:    ExportInfo:
+# CHECK-NEXT:      - Name:            tls1
+# CHECK-NEXT:        Flags:           [ TLS ]
+# CHECK-NEXT:  - Type:            TYPE
+
+#      CHECK:  - Type:            GLOBAL
+# CHECK-NEXT:    Globals:
+# CHECK-NEXT:      - Index:           2
+# CHECK-NEXT:        Type:            I32
+# CHECK-NEXT:        Mutable:         false
+# CHECK-NEXT:        InitExpr:
+# CHECK-NEXT:          Opcode:          I32_CONST
+# CHECK-NEXT:          Value:           0
+
+#      CHECK:  - Type:            EXPORT
+# CHECK-NEXT:    Exports:
+# CHECK-NEXT:      - Name:            __wasm_call_ctors
+# CHECK-NEXT:        Kind:            FUNCTION
+# CHECK-NEXT:        Index:           0
+# CHECK-NEXT:      - Name:            tls1
+# CHECK-NEXT:        Kind:            GLOBAL
+# CHECK-NEXT:        Index:           2

lld/test/wasm/tls-import.s

@@ -1,5 +1,5 @@
 # Test that linking without shared memory causes __tls_base to be
-# internalized
+# internalized.
 
 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
 
@@ -13,14 +13,20 @@ get_tls1:
   i32.add
   end_function
 
+.globl get_tls1_got
+get_tls1_got:
+  .functype get_tls1_got () -> (i32)
+  global.get tls1@GOT@TLS
+  end_function
+
 .section  .data.no_tls,"",@
 .globl  no_tls
 .p2align  2
 no_tls:
   .int32  42
   .size no_tls, 4
 
-.section  .tdata.tls1,"",@
+.section  .tdata.tls1,"T",@
 .globl  tls1
 .p2align  2
 tls1:
@@ -58,6 +64,13 @@ tls1:
 # CHECK-NEXT:         InitExpr:
 # CHECK-NEXT:           Opcode:          I32_CONST
 # CHECK-NEXT:           Value:           1024
+# GOT.data.internal.tls1
+# CHECK-NEXT:       - Index:           2
+# CHECK-NEXT:         Type:            I32
+# CHECK-NEXT:         Mutable:         false
+# CHECK-NEXT:         InitExpr:
+# CHECK-NEXT:           Opcode:          I32_CONST
+# CHECK-NEXT:           Value:           1024
 # CHECK-NEXT:   - Type:            EXPORT
 
 #      CHECK:  - Type:            DATA

lld/test/wasm/tls-non-shared-memory.s

@@ -139,12 +139,6 @@ void scanRelocations(InputChunk *chunk) {
     }
 
     if (config->isPic) {
-      if (sym->isTLS() && sym->isUndefined()) {
-        error(toString(file) +
-              ": TLS symbol is undefined, but TLS symbols cannot yet be "
-              "imported: `" +
-              toString(*sym) + "`");
-      }
       switch (reloc.Type) {
       case R_WASM_TABLE_INDEX_SLEB:
       case R_WASM_TABLE_INDEX_SLEB64:

lld/wasm/Relocations.cpp

@@ -74,6 +74,7 @@ DefinedFunction *WasmSym::callDtors;
 DefinedFunction *WasmSym::initMemory;
 DefinedFunction *WasmSym::applyDataRelocs;
 DefinedFunction *WasmSym::applyGlobalRelocs;
+DefinedFunction *WasmSym::applyGlobalTLSRelocs;
 DefinedFunction *WasmSym::initTLS;
 DefinedFunction *WasmSym::startFunction;
 DefinedData *WasmSym::dsoHandle;

lld/wasm/Symbols.cpp

@@ -552,10 +552,15 @@ struct WasmSym {
   static DefinedFunction *applyDataRelocs;
 
   // __wasm_apply_global_relocs
-  // Function that applies relocations to data segment post-instantiation.
+  // Function that applies relocations to wasm globals post-instantiation.
   // Unlike __wasm_apply_data_relocs this needs to run on every thread.
   static DefinedFunction *applyGlobalRelocs;
 
+  // __wasm_apply_global_tls_relocs
+  // Like applyGlobalRelocs but for globals that hold TLS addresess.  These
+  // must be delayed until __wasm_init_tls.
+  static DefinedFunction *applyGlobalTLSRelocs;
+
   // __wasm_init_tls
   // Function that allocates thread-local storage and initializes it.
   static DefinedFunction *initTLS;