[RISCV] Use the thread local stack protector for Android targets

[ilovepi]

Android supports per thread stack protectors that are individually managed and
initialized, which can provide stronger protections than using the global stack
protector cookie. This patch matches the convention for other architectures
targeting Android platforms.

[llvmbot]

@llvm/pr-subscribers-backend-risc-v

Author: Paul Kirth (ilovepi)

Changes

Android supports per thread stack protectors that are individually managed and
initialized, which can provide stronger protections than using the global stack
protector cookie. This patch matches the convention for other architectures
targeting Android platforms.

---

Full diff: https://github.com/llvm/llvm-project/pull/87672.diff

1 Files Affected:

• (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+6)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 279d8a435a04ca..5bd96d5e2c403c 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -20657,6 +20657,12 @@ Value *RISCVTargetLowering::getIRStackGuard(IRBuilderBase &IRB) const {
   if (Subtarget.isTargetFuchsia())
     return useTpOffset(IRB, -0x10);
 
+  // Android provides a fixed TLS slot for the stack cookie. See the definition
+  // of TLS_SLOT_STACK_GUARD in
+  // https://android.googlesource.com/platform/bionic/+/master/libc/platform/bionic/tls_defines.h
+  if (Subtarget.isTargetAndroid())
+    return useTpOffset(IRB, -0x18);
+
   return TargetLowering::getIRStackGuard(IRB);
 }
 

[enh-google]

s/master/main/ in the url to get the current version. (master "works" but it's frozen in time; main will track future changes.)

otherwise lgtm...

[topperc]

s/master/main/ in the url to get the current version. (master "works" but it's frozen in time; main will track future changes.)

otherwise lgtm...

Probably someone should update AArch64 which has the same comment?

[rprichard]

LGTM

[ilovepi]

s/master/main/ in the url to get the current version. (master "works" but it's frozen in time; main will track future changes.)
otherwise lgtm...

Probably someone should update AArch64 which has the same comment?

Done in #87726

[ilovepi]

I plan to land this today, after presubmits are green.