From b5cc658ab4113b4db4f709dbec258910696990bd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Sun, 6 Jul 2025 22:19:08 +0200
Subject: [PATCH] llvm: Use emulated TLS when appropriate for the target

Closes #24236.
---
 src/codegen/llvm.zig          |  1 +
 src/codegen/llvm/bindings.zig |  1 +
 src/main.zig                  |  2 +-
 src/target.zig                | 13 +++++++++++++
 src/zig_llvm.cpp              |  6 +++++-
 src/zig_llvm.h                |  2 +-
 6 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index 27092a1de8..db628eab5d 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -1047,6 +1047,7 @@ pub const Object = struct {
             comp.data_sections,
             float_abi,
             if (target_util.llvmMachineAbi(&comp.root_mod.resolved_target.result)) |s| s.ptr else null,
+            target_util.useEmulatedTls(&comp.root_mod.resolved_target.result),
         );
         errdefer target_machine.dispose();
 
diff --git a/src/codegen/llvm/bindings.zig b/src/codegen/llvm/bindings.zig
index 5d2d4c2a99..7fa2a7da43 100644
--- a/src/codegen/llvm/bindings.zig
+++ b/src/codegen/llvm/bindings.zig
@@ -79,6 +79,7 @@ pub const TargetMachine = opaque {
         data_sections: bool,
         float_abi: FloatABI,
         abi_name: ?[*:0]const u8,
+        emulated_tls: bool,
     ) *TargetMachine;
 
     pub const dispose = LLVMDisposeTargetMachine;
diff --git a/src/main.zig b/src/main.zig
index 7b7d5be59a..aa20b8fae1 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -6324,7 +6324,7 @@ fn cmdDumpLlvmInts(
         if (llvm.Target.getFromTriple(triple, &target, &error_message) != .False) @panic("bad");
         break :t target;
     };
-    const tm = llvm.TargetMachine.create(target, triple, null, null, .None, .Default, .Default, false, false, .Default, null);
+    const tm = llvm.TargetMachine.create(target, triple, null, null, .None, .Default, .Default, false, false, .Default, null, false);
     const dl = tm.createTargetDataLayout();
     const context = llvm.Context.create();
 
diff --git a/src/target.zig b/src/target.zig
index 28cdf3e3aa..7852dda7a4 100644
--- a/src/target.zig
+++ b/src/target.zig
@@ -85,6 +85,19 @@ pub fn defaultSingleThreaded(target: *const std.Target) bool {
     return false;
 }
 
+pub fn useEmulatedTls(target: *const std.Target) bool {
+    if (target.abi.isAndroid()) {
+        if (target.os.version_range.linux.android < 29) return true;
+        return false;
+    }
+    if (target.abi.isOpenHarmony()) return true;
+    return switch (target.os.tag) {
+        .openbsd => true,
+        .windows => target.abi == .cygnus,
+        else => false,
+    };
+}
+
 pub fn hasValgrindSupport(target: *const std.Target, backend: std.builtin.CompilerBackend) bool {
     // We can't currently output the necessary Valgrind client request assembly when using the C
     // backend and compiling with an MSVC-like compiler.
diff --git a/src/zig_llvm.cpp b/src/zig_llvm.cpp
index fe4e421dc3..c9a30bb167 100644
--- a/src/zig_llvm.cpp
+++ b/src/zig_llvm.cpp
@@ -83,7 +83,7 @@ static const bool assertions_on = false;
 LLVMTargetMachineRef ZigLLVMCreateTargetMachine(LLVMTargetRef T, const char *Triple,
     const char *CPU, const char *Features, LLVMCodeGenOptLevel Level, LLVMRelocMode Reloc,
     LLVMCodeModel CodeModel, bool function_sections, bool data_sections, ZigLLVMFloatABI float_abi,
-    const char *abi_name)
+    const char *abi_name, bool emulated_tls)
 {
     std::optional<Reloc::Model> RM;
     switch (Reloc){
@@ -149,6 +149,10 @@ LLVMTargetMachineRef ZigLLVMCreateTargetMachine(LLVMTargetRef T, const char *Tri
         opt.MCOptions.ABIName = abi_name;
     }
 
+    if (emulated_tls) {
+        opt.EmulatedTLS = true;
+    }
+
     TargetMachine *TM = reinterpret_cast<Target*>(T)->createTargetMachine(Triple, CPU, Features, opt, RM, CM,
             OL, JIT);
     return reinterpret_cast<LLVMTargetMachineRef>(TM);
diff --git a/src/zig_llvm.h b/src/zig_llvm.h
index e2dba338c3..db331512bd 100644
--- a/src/zig_llvm.h
+++ b/src/zig_llvm.h
@@ -105,7 +105,7 @@ ZIG_EXTERN_C bool ZigLLVMTargetMachineEmitToFile(LLVMTargetMachineRef targ_machi
 ZIG_EXTERN_C LLVMTargetMachineRef ZigLLVMCreateTargetMachine(LLVMTargetRef T, const char *Triple,
     const char *CPU, const char *Features, LLVMCodeGenOptLevel Level, LLVMRelocMode Reloc,
     LLVMCodeModel CodeModel, bool function_sections, bool data_sections, ZigLLVMFloatABI float_abi,
-    const char *abi_name);
+    const char *abi_name, bool emulated_tls);
 
 ZIG_EXTERN_C void ZigLLVMSetOptBisectLimit(LLVMContextRef context_ref, int limit);