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

Use emulated TLS for android

This is a reopen of rust-lang#96317 . many android devices still only use 128 pthread keys, so using emutls can be helpful.

r? `@Amanieu`

Author: bors

compiler/rustc_codegen_gcc/src/context.rs

@@ -569,5 +569,6 @@ fn to_gcc_tls_mode(tls_model: TlsModel) -> gccjit::TlsModel {
         TlsModel::LocalDynamic => gccjit::TlsModel::LocalDynamic,
         TlsModel::InitialExec => gccjit::TlsModel::InitialExec,
         TlsModel::LocalExec => gccjit::TlsModel::LocalExec,
+        TlsModel::EmulatedTls => gccjit::TlsModel::GlobalDynamic,
     }
 }

compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs

@@ -39,7 +39,7 @@ impl OwnedTargetMachine {
         split_dwarf_file: &CStr,
         output_obj_file: &CStr,
         debug_info_compression: &CStr,
-        force_emulated_tls: bool,
+        use_emulated_tls: bool,
         args_cstr_buff: &[u8],
     ) -> Result<Self, LlvmError<'static>> {
         assert!(args_cstr_buff.len() > 0);
@@ -71,7 +71,7 @@ impl OwnedTargetMachine {
                 split_dwarf_file.as_ptr(),
                 output_obj_file.as_ptr(),
                 debug_info_compression.as_ptr(),
-                force_emulated_tls,
+                use_emulated_tls,
                 args_cstr_buff.as_ptr() as *const c_char,
                 args_cstr_buff.len(),
             )

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -33,7 +33,7 @@ use rustc_session::config::{self, Lto, OutputType, Passes, SplitDwarfKind, Switc
 use rustc_session::Session;
 use rustc_span::symbol::sym;
 use rustc_span::InnerSpan;
-use rustc_target::spec::{CodeModel, RelocModel, SanitizerSet, SplitDebuginfo};
+use rustc_target::spec::{CodeModel, RelocModel, SanitizerSet, SplitDebuginfo, TlsModel};
 
 use crate::llvm::diagnostic::OptimizationDiagnosticKind;
 use libc::{c_char, c_int, c_uint, c_void, size_t};
@@ -223,7 +223,7 @@ pub fn target_machine_factory(
 
     let path_mapping = sess.source_map().path_mapping().clone();
 
-    let force_emulated_tls = sess.target.force_emulated_tls;
+    let use_emulated_tls = matches!(sess.tls_model(), TlsModel::EmulatedTls);
 
     // copy the exe path, followed by path all into one buffer
     // null terminating them so we can use them as null terminated strings
@@ -297,7 +297,7 @@ pub fn target_machine_factory(
             &split_dwarf_file,
             &output_obj_file,
             &debuginfo_compression,
-            force_emulated_tls,
+            use_emulated_tls,
             &args_cstr_buff,
         )
     })

compiler/rustc_codegen_llvm/src/context.rs

@@ -120,6 +120,7 @@ fn to_llvm_tls_model(tls_model: TlsModel) -> llvm::ThreadLocalMode {
         TlsModel::LocalDynamic => llvm::ThreadLocalMode::LocalDynamic,
         TlsModel::InitialExec => llvm::ThreadLocalMode::InitialExec,
         TlsModel::LocalExec => llvm::ThreadLocalMode::LocalExec,
+        TlsModel::EmulatedTls => llvm::ThreadLocalMode::GeneralDynamic,
     }
 }
 

compiler/rustc_codegen_llvm/src/lib.rs

@@ -305,7 +305,13 @@ impl CodegenBackend for LlvmCodegenBackend {
             }
             PrintKind::TlsModels => {
                 writeln!(out, "Available TLS models:");
-                for name in &["global-dynamic", "local-dynamic", "initial-exec", "local-exec"] {
+                for name in &[
+                    "global-dynamic",
+                    "local-dynamic",
+                    "initial-exec",
+                    "local-exec",
+                    "emulated-tls",
+                ] {
                     writeln!(out, "    {name}");
                 }
                 writeln!(out);

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -1748,7 +1748,9 @@ fn exported_symbols_for_non_proc_macro(tcx: TyCtxt<'_>, crate_type: CrateType) -
     let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
     for_each_exported_symbols_include_dep(tcx, crate_type, |symbol, info, cnum| {
         if info.level.is_below_threshold(export_threshold) {
-            symbols.push(symbol_export::symbol_name_for_instance_in_crate(tcx, symbol, cnum));
+            symbols.push(symbol_export::exporting_symbol_name_for_instance_in_crate(
+                tcx, symbol, cnum,
+            ));
         }
     });
 

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -16,7 +16,7 @@ use rustc_middle::ty::{self, SymbolName, TyCtxt};
 use rustc_middle::ty::{GenericArgKind, GenericArgsRef};
 use rustc_middle::util::Providers;
 use rustc_session::config::{CrateType, OomStrategy};
-use rustc_target::spec::SanitizerSet;
+use rustc_target::spec::{SanitizerSet, TlsModel};
 
 pub fn threshold(tcx: TyCtxt<'_>) -> SymbolExportLevel {
     crates_export_threshold(tcx.crate_types())
@@ -608,6 +608,25 @@ pub fn linking_symbol_name_for_instance_in_crate<'tcx>(
     format!("{prefix}{undecorated}{suffix}{args_in_bytes}")
 }
 
+pub fn exporting_symbol_name_for_instance_in_crate<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    symbol: ExportedSymbol<'tcx>,
+    cnum: CrateNum,
+) -> String {
+    let undecorated = symbol_name_for_instance_in_crate(tcx, symbol, cnum);
+
+    if matches!(tcx.sess.tls_model(), TlsModel::EmulatedTls)
+        && let ExportedSymbol::NonGeneric(def_id) = symbol
+        && tcx.is_thread_local_static(def_id)
+    {
+        // When using emutls, LLVM will add the `__emutls_v.` prefix to thread local symbols,
+        // and exported symbol name need to match this.
+        format!("__emutls_v.{undecorated}")
+    } else {
+        undecorated
+    }
+}
+
 fn wasm_import_module_map(tcx: TyCtxt<'_>, cnum: CrateNum) -> FxHashMap<DefId, String> {
     // Build up a map from DefId to a `NativeLib` structure, where
     // `NativeLib` internally contains information about

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.

compiler/rustc_target/src/spec/base/android.rs

@@ -1,11 +1,12 @@
-use crate::spec::{base, SanitizerSet, TargetOptions};
+use crate::spec::{base, SanitizerSet, TargetOptions, TlsModel};
 
 pub fn opts() -> TargetOptions {
     let mut base = base::linux::opts();
     base.os = "android".into();
     base.is_like_android = true;
     base.default_dwarf_version = 2;
-    base.has_thread_local = false;
+    base.tls_model = TlsModel::EmulatedTls;
+    base.has_thread_local = true;
     base.supported_sanitizers = SanitizerSet::ADDRESS;
     // This is for backward compatibility, see https://github.com/rust-lang/rust/issues/49867
     // for context. (At that time, there was no `-C force-unwind-tables`, so the only solution

compiler/rustc_target/src/spec/base/linux_ohos.rs

@@ -1,11 +1,11 @@
-use crate::spec::{base, TargetOptions};
+use crate::spec::{base, TargetOptions, TlsModel};
 
 pub fn opts() -> TargetOptions {
     let mut base = base::linux::opts();
 
     base.env = "ohos".into();
     base.crt_static_default = false;
-    base.force_emulated_tls = true;
+    base.tls_model = TlsModel::EmulatedTls;
     base.has_thread_local = false;
 
     base

compiler/rustc_target/src/spec/mod.rs

@@ -929,6 +929,7 @@ pub enum TlsModel {
     LocalDynamic,
     InitialExec,
     LocalExec,
+    EmulatedTls,
 }
 
 impl FromStr for TlsModel {
@@ -942,6 +943,7 @@ impl FromStr for TlsModel {
             "local-dynamic" => TlsModel::LocalDynamic,
             "initial-exec" => TlsModel::InitialExec,
             "local-exec" => TlsModel::LocalExec,
+            "emulated-tls" => TlsModel::EmulatedTls,
             _ => return Err(()),
         })
     }
@@ -954,6 +956,7 @@ impl ToJson for TlsModel {
             TlsModel::LocalDynamic => "local-dynamic",
             TlsModel::InitialExec => "initial-exec",
             TlsModel::LocalExec => "local-exec",
+            TlsModel::EmulatedTls => "emulated-tls",
         }
         .to_json()
     }
@@ -2190,9 +2193,6 @@ pub struct TargetOptions {
 
     /// Whether the target supports XRay instrumentation.
     pub supports_xray: bool,
-
-    /// Forces the use of emulated TLS (__emutls_get_address)
-    pub force_emulated_tls: bool,
 }
 
 /// Add arguments for the given flavor and also for its "twin" flavors
@@ -2408,7 +2408,6 @@ impl Default for TargetOptions {
             entry_name: "main".into(),
             entry_abi: Conv::C,
             supports_xray: false,
-            force_emulated_tls: false,
         }
     }
 }
@@ -3112,7 +3111,6 @@ impl Target {
         key!(entry_name);
         key!(entry_abi, Conv)?;
         key!(supports_xray, bool);
-        key!(force_emulated_tls, bool);
 
         if base.is_builtin {
             // This can cause unfortunate ICEs later down the line.
@@ -3368,7 +3366,6 @@ impl ToJson for Target {
         target_option_val!(entry_name);
         target_option_val!(entry_abi);
         target_option_val!(supports_xray);
-        target_option_val!(force_emulated_tls);
 
         if let Some(abi) = self.default_adjusted_cabi {
             d.insert("default-adjusted-cabi".into(), Abi::name(abi).to_json());

library/std/src/sys/unix/thread_local_dtor.rs

@@ -12,7 +12,13 @@
 // compiling from a newer linux to an older linux, so we also have a
 // fallback implementation to use as well.
 #[allow(unexpected_cfgs)]
-#[cfg(any(target_os = "linux", target_os = "fuchsia", target_os = "redox", target_os = "hurd"))]
+#[cfg(any(
+    target_os = "linux",
+    target_os = "android",
+    target_os = "fuchsia",
+    target_os = "redox",
+    target_os = "hurd"
+))]
 // FIXME: The Rust compiler currently omits weakly function definitions (i.e.,
 // __cxa_thread_atexit_impl) and its metadata from LLVM IR.
 #[no_sanitize(cfi, kcfi)]

src/doc/unstable-book/src/compiler-flags/tls-model.md

@@ -20,6 +20,8 @@ loaded at program startup.
 The TLS data must not be in a library loaded after startup (via `dlopen`).
 - `local-exec` - model usable only if the TLS data is defined directly in the executable,
 but not in a shared library, and is accessed only from that executable.
+- `emulated-tls` - Uses thread-specific data keys to implement emulated TLS.
+It is like using a general-dynamic TLS model for all modes.
 
 `rustc` and LLVM may use a more optimized model than specified if they know that we are producing
 an executable rather than a library, or that the `static` item is private enough.