From f900ee331dfe95493390e1beecb82a277158b60b Mon Sep 17 00:00:00 2001
From: hyd-dev <yd-huang@outlook.com>
Date: Tue, 23 Mar 2021 02:38:30 +0800
Subject: [PATCH] Allow not emitting `uwtable` on Android

---
 compiler/rustc_session/src/session.rs          |  2 +-
 compiler/rustc_target/src/spec/android_base.rs |  5 ++++-
 compiler/rustc_target/src/spec/mod.rs          |  7 +++++++
 src/test/codegen/default-requires-uwtable.rs   | 15 +++++++++++++++
 src/test/codegen/force-no-unwind-tables.rs     |  7 +++++++
 5 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 src/test/codegen/default-requires-uwtable.rs
 create mode 100644 src/test/codegen/force-no-unwind-tables.rs

diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index fc57b6b8acedf..203af36b05313 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -863,7 +863,7 @@ impl Session {
         } else if self.target.requires_uwtable {
             true
         } else {
-            self.opts.cg.force_unwind_tables.unwrap_or(false)
+            self.opts.cg.force_unwind_tables.unwrap_or(self.target.default_uwtable)
         }
     }
 
diff --git a/compiler/rustc_target/src/spec/android_base.rs b/compiler/rustc_target/src/spec/android_base.rs
index f6fbe7cd5f622..c7d2f2329ee86 100644
--- a/compiler/rustc_target/src/spec/android_base.rs
+++ b/compiler/rustc_target/src/spec/android_base.rs
@@ -12,7 +12,10 @@ pub fn opts() -> TargetOptions {
     base.dwarf_version = Some(2);
     base.position_independent_executables = true;
     base.has_elf_tls = false;
-    base.requires_uwtable = true;
+    // 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
+    // was to always emit `uwtable`).
+    base.default_uwtable = true;
     base.crt_static_respected = false;
     base
 }
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index c9fffd213d768..ddfd82625221f 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -1111,6 +1111,10 @@ pub struct TargetOptions {
     /// unwinders.
     pub requires_uwtable: bool,
 
+    /// Whether or not to emit `uwtable` attributes on functions if `-C force-unwind-tables`
+    /// is not specified and `uwtable` is not required on this target.
+    pub default_uwtable: bool,
+
     /// Whether or not SIMD types are passed by reference in the Rust ABI,
     /// typically required if a target can be compiled with a mixed set of
     /// target features. This is `true` by default, and `false` for targets like
@@ -1248,6 +1252,7 @@ impl Default for TargetOptions {
             default_hidden_visibility: false,
             emit_debug_gdb_scripts: true,
             requires_uwtable: false,
+            default_uwtable: false,
             simd_types_indirect: true,
             limit_rdylib_exports: true,
             override_export_symbols: None,
@@ -1711,6 +1716,7 @@ impl Target {
         key!(default_hidden_visibility, bool);
         key!(emit_debug_gdb_scripts, bool);
         key!(requires_uwtable, bool);
+        key!(default_uwtable, bool);
         key!(simd_types_indirect, bool);
         key!(limit_rdylib_exports, bool);
         key!(override_export_symbols, opt_list);
@@ -1947,6 +1953,7 @@ impl ToJson for Target {
         target_option_val!(default_hidden_visibility);
         target_option_val!(emit_debug_gdb_scripts);
         target_option_val!(requires_uwtable);
+        target_option_val!(default_uwtable);
         target_option_val!(simd_types_indirect);
         target_option_val!(limit_rdylib_exports);
         target_option_val!(override_export_symbols);
diff --git a/src/test/codegen/default-requires-uwtable.rs b/src/test/codegen/default-requires-uwtable.rs
new file mode 100644
index 0000000000000..d4c4200c5d230
--- /dev/null
+++ b/src/test/codegen/default-requires-uwtable.rs
@@ -0,0 +1,15 @@
+// revisions: WINDOWS ANDROID
+// needs-llvm-components: x86 arm
+// compile-flags: -C panic=abort
+// [WINDOWS] compile-flags: --target=x86_64-pc-windows-msvc
+// [ANDROID] compile-flags: --target=armv7-linux-androideabi
+
+#![feature(no_core, lang_items)]
+#![crate_type = "lib"]
+#![no_core]
+
+#[lang = "sized"]
+trait Sized {}
+
+// CHECK: attributes #{{.*}} uwtable
+pub fn foo() {}
diff --git a/src/test/codegen/force-no-unwind-tables.rs b/src/test/codegen/force-no-unwind-tables.rs
new file mode 100644
index 0000000000000..dc77e6cb70917
--- /dev/null
+++ b/src/test/codegen/force-no-unwind-tables.rs
@@ -0,0 +1,7 @@
+// compile-flags: -C no-prepopulate-passes -C panic=abort -C force-unwind-tables=n
+// ignore-windows
+
+#![crate_type="lib"]
+
+// CHECK-NOT: attributes #{{.*}} uwtable
+pub fn foo() {}