Pack relocations for Android API >= 28 (llvm#117624)

Patch copied from:
android/ndk#909 (comment)
Fixes: android/ndk#909

Author: hiraditya

clang/lib/Driver/ToolChains/Linux.cpp

@@ -256,6 +256,24 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
       ExtraOpts.push_back("-z");
       ExtraOpts.push_back("max-page-size=16384");
     }
+    if (Triple.isAndroidVersionLT(29)) {
+      // https://github.com/android/ndk/issues/1196
+      // The unwinder used by the crash handler on versions of Android prior to
+      // API 29 did not correctly handle binaries built with rosegment, which is
+      // enabled by default for LLD. Android only supports LLD, so it's not an
+      // issue that this flag is not accepted by other linkers.
+      ExtraOpts.push_back("--no-rosegment");
+    }
+    if (!Triple.isAndroidVersionLT(28)) {
+      // Android supports relr packing starting with API 28 and had its own
+      // flavor (--pack-dyn-relocs=android) starting in API 23.
+      // TODO: It's possible to use both with --pack-dyn-relocs=android+relr,
+      // but we need to gather some data on the impact of that form before we
+      // can know if it's a good default.
+      // On the other hand, relr should always be an improvement.
+      ExtraOpts.push_back("--use-android-relr-tags");
+      ExtraOpts.push_back("--pack-dyn-relocs=relr");
+    }
   }
 
   if (GCCInstallation.getParentLibPath().contains("opt/rh/"))

clang/test/Driver/linux-ld.c

@@ -940,6 +940,36 @@
 // CHECK-ANDROID-HASH-STYLE-M: "{{.*}}ld{{(.exe)?}}"
 // CHECK-ANDROID-HASH-STYLE-M: "--hash-style=gnu"
 
+// Check that we pass --no-rosegment for pre-29 Android versions and do not for
+// 29+.
+// RUN: %clang %s -### -o %t.o 2>&1 \
+// RUN:     --target=armv7-linux-android28 \
+// RUN:   | FileCheck --check-prefix=CHECK-ANDROID-ROSEGMENT-28 %s
+// CHECK-ANDROID-ROSEGMENT-28: "{{.*}}ld{{(.exe)?}}"
+// CHECK-ANDROID-ROSEGMENT-28: "--no-rosegment"
+//
+// RUN: %clang %s -### -o %t.o 2>&1 \
+// RUN:     --target=armv7-linux-android29 \
+// RUN:   | FileCheck --check-prefix=CHECK-ANDROID-ROSEGMENT-29 %s
+// CHECK-ANDROID-ROSEGMENT-29: "{{.*}}ld{{(.exe)?}}"
+// CHECK-ANDROID-ROSEGMENT-29-NOT: "--no-rosegment"
+
+// Check that we pass --pack-dyn-relocs=relr for API 28+ and not before.
+// RUN: %clang %s -### -o %t.o 2>&1 \
+// RUN:     --target=armv7-linux-android27 \
+// RUN:   | FileCheck --check-prefix=CHECK-ANDROID-RELR-27 %s
+// CHECK-ANDROID-RELR-27: "{{.*}}ld{{(.exe)?}}"
+// CHECK-ANDROID-RELR-27-NOT: "--pack-dyn-relocs=relr"
+// CHECK-ANDROID-RELR-27-NOT: "--pack-dyn-relocs=android+relr"
+//
+// RUN: %clang %s -### -o %t.o 2>&1 \
+// RUN:     --target=armv7-linux-android28 \
+// RUN:   | FileCheck --check-prefix=CHECK-ANDROID-RELR-28 %s
+// CHECK-ANDROID-RELR-28: "{{.*}}ld{{(.exe)?}}"
+// CHECK-ANDROID-RELR-28: "--use-android-relr-tags"
+// CHECK-ANDROID-RELR-28: "--pack-dyn-relocs=relr"
+// CHECK-ANDROID-RELR-28-NOT: "--pack-dyn-relocs=android+relr"
+
 // RUN: %clang -### %s -no-pie 2>&1 --target=mips64-linux-gnuabin32 \
 // RUN:   | FileCheck --check-prefix=CHECK-MIPS64EL-GNUABIN32 %s
 // CHECK-MIPS64EL-GNUABIN32: "{{.*}}ld{{(.exe)?}}"