Auto merge of #117873 - quininer:android-emutls, r=Amanieu

Add emulated TLS support

This is a reopen of https://github.com/rust-lang/rust/pull/96317 . many android devices still only use 128 pthread keys, so using emutls can be helpful.

Currently LLVM uses emutls by default for some targets (such as android, openbsd), but rust does not use it, because `has_thread_local` is false.

This commit has some changes to allow users to enable emutls:

1. add `-Zhas-thread-local` flag to specify that std uses `#[thread_local]` instead of pthread key.
2. when using emutls, decorate symbol names to find thread local symbol correctly.
3. change `-Zforce-emulated-tls` to `-Ztls-model=emulated` to explicitly specify whether to generate emutls.

r? `@Amanieu`

1 files changed, 3 insertions, 7 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
index 0edcac93b62..55e1c84c8a2 100644
--- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
@@ -410,7 +410,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     const char *SplitDwarfFile,
     const char *OutputObjFile,
     const char *DebugInfoCompression,
-    bool ForceEmulatedTls,
+    bool UseEmulatedTls,
     const char *ArgsCstrBuff, size_t ArgsCstrBuffLen) {
 
   auto OptLevel = fromRust(RustOptLevel);
@@ -456,13 +456,9 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   Options.UseInitArray = UseInitArray;
 
 #if LLVM_VERSION_LT(17, 0)
-  if (ForceEmulatedTls) {
-    Options.ExplicitEmulatedTLS = true;
-    Options.EmulatedTLS = true;
-  }
-#else
-  Options.EmulatedTLS = ForceEmulatedTls || Trip.hasDefaultEmulatedTLS();
+  Options.ExplicitEmulatedTLS = true;
 #endif
+  Options.EmulatedTLS = UseEmulatedTls;
 
   if (TrapUnreachable) {
     // Tell LLVM to codegen `unreachable` into an explicit trap instruction.