Start reserving x18 by default on Android targets.

[kcc]

Don't you need a test?
srhines@, what kind of documentation change need to be done?

[pcc]

• Add test

[pcc]

In D45588#1066620, @kcc wrote:

Don't you need a test?

Probably the easiest way to test this is to check that clang -fsanitize=shadow-call-stack does not complain about needing -ffixed-x18, so that is what I've done.

[kcc]

This test is great, but I'd like to also see some more direct test, maybe something in tools/clang/test/Driver/aarch64-fixed-x18.c?

LGTM for the code, but I still want to hear LGTM from srhines@

[pcc]

• Add LLVM code generation test

[pcc]

In D45588#1067402, @kcc wrote:

This test is great, but I'd like to also see some more direct test, maybe something in tools/clang/test/Driver/aarch64-fixed-x18.c?

That won't test what we want here because the platform defaults are not applied via target features. I added a case for Android to one of the code generation tests.

[kcc]

Yep, that's the one, thanks!

[pcc]

@srhines Ping.

[srhines]

Sorry, this got buried in my inbox back in April right before EuroLLVM.

clang/test/Driver/sanitizer-ld.c

 // CHECK-SHADOWCALLSTACK-LINUX-AARCH64: '-fsanitize=shadow-call-stack' only allowed with '-ffixed-x18'
 
 // RUN: %clang -fsanitize=shadow-call-stack %s -### -o %t.o 2>&1 \
 // RUN:     -target aarch64-unknown-linux -fuse-ld=ld -ffixed-x18 \
 // RUN:   | FileCheck --check-prefix=CHECK-SHADOWCALLSTACK-LINUX-AARCH64-X18 %s
 // RUN: %clang -fsanitize=shadow-call-stack %s -### -o %t.o 2>&1 \
 // RUN:     -target arm64-unknown-ios -fuse-ld=ld \
 // RUN:   | FileCheck --check-prefix=CHECK-SHADOWCALLSTACK-LINUX-AARCH64-X18 %s
+// RUN: %clang -fsanitize=shadow-call-stack %s -### -o %t.o 2>&1 \
+// RUN:     -target aarch64-unknown-linux-android -fuse-ld=ld \
+// RUN:   | FileCheck --check-prefix=CHECK-SHADOWCALLSTACK-LINUX-AARCH64-X18 %s
 // CHECK-SHADOWCALLSTACK-LINUX-AARCH64-X18-NOT: error:
 
 // RUN: %clang -fsanitize=shadow-call-stack %s -### -o %t.o 2>&1 \
 // RUN:     -target x86-unknown-linux -fuse-ld=ld \
 // RUN:   | FileCheck --check-prefix=CHECK-SHADOWCALLSTACK-LINUX-X86 %s
 // CHECK-SHADOWCALLSTACK-LINUX-X86: error: unsupported option '-fsanitize=shadow-call-stack' for target 'x86-unknown-linux'
 
 // RUN: %clang -fsanitize=shadow-call-stack %s -### -o %t.o 2>&1 \

llvm/lib/Support/TargetParser.cpp

 }
 
 // Version number (ex. v8 = 8).
 unsigned llvm::AArch64::parseArchVersion(StringRef Arch) {
   return ARM::parseArchVersion(Arch);
 }
 
 bool llvm::AArch64::isX18ReservedByDefault(const Triple &TT) {
-  return TT.isOSDarwin() || TT.isOSFuchsia() || TT.isOSWindows();
+  return TT.isAndroid() || TT.isOSDarwin() || TT.isOSFuchsia() ||
+         TT.isOSWindows();
 }

llvm/test/CodeGen/AArch64/arm64-platform-reg.ll

 ; RUN: llc -mtriple=arm64-apple-ios -mattr=+reserve-x18 -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 ; RUN: llc -mtriple=arm64-freebsd-gnu -mattr=+reserve-x18 -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 ; RUN: llc -mtriple=arm64-linux-gnu -o - %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-linux-android -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 ; RUN: llc -mtriple=aarch64-fuchsia -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 ; RUN: llc -mtriple=aarch64-windows -o - %s | FileCheck %s --check-prefix=CHECK-RESERVE-X18
 
 ; x18 is reserved as a platform register on Darwin but not on other
 ; systems. Create loads of register pressure and make sure this is respected.
 
 ; Also, fp must always refer to a valid frame record, even if it's not the one
 ; of the current function, so it shouldn't be used either.