[AArch64] Make width of stack protector guard value load configurable. (#195379)

Certain embedded targets store the value of the stack protector global
in an MMIO register, which requires a load of a specific width. Allow
changing the backend to emit a 4-byte load for the value of the stack
protector, instead of an 8-byte load. (Or vice versa for an ilp32
target.)

The current version of the patch has a limitation: it still allocates a
pointer-sized stack slot for the guard. This could be fixed in the
future, if it becomes relevant.

GitOrigin-RevId: 57fcde7df138c64793cf349bb97303e921f9c5f6

include/clang/Basic/CodeGenOptions.def

diff --git a/include/clang/Basic/CodeGenOptions.def b/include/clang/Basic/CodeGenOptions.def
index fd0b6d9..aa36de6 100644
--- a/include/clang/Basic/CodeGenOptions.def
+++ b/include/clang/Basic/CodeGenOptions.def
@@ -433,6 +433,9 @@
 /// The default stack protector guard offset to use.
 VALUE_CODEGENOPT(StackProtectorGuardOffset, 32, INT_MAX, Benign)
 
+/// The width to use for the stack protector guard value.
+VALUE_CODEGENOPT(StackProtectorGuardValueWidth, 32, UINT_MAX, Benign)
+
 /// Number of path components to strip when emitting checks. (0 == full
 /// filename)
 VALUE_CODEGENOPT(EmitCheckPathComponentsToStrip, 32, 0, Benign)

include/clang/Options/Options.td

diff --git a/include/clang/Options/Options.td b/include/clang/Options/Options.td
index 0dc74ea..71ad4b7 100644
--- a/include/clang/Options/Options.td
+++ b/include/clang/Options/Options.td
@@ -6082,6 +6082,15 @@
   Visibility<[ClangOption, CC1Option]>,
   HelpText<"Use the given offset for addressing the stack-protector guard">,
   MarshallingInfoInt<CodeGenOpts<"StackProtectorGuardOffset">, "INT_MAX", "int">;
+def mstack_protector_guard_value_width_EQ : Joined<["-"], "mstack-protector-guard-value-width=">, Group<m_Group>,
+  Visibility<[ClangOption, CC1Option]>,
+  HelpText<"Use the given width for the value of the the stack-protector guard (AArch64-only)">,
+  MarshallingInfoInt<CodeGenOpts<"StackProtectorGuardValueWidth">, "UINT_MAX", "unsigned">,
+  DocBrief<[{Set the width of the stack-protector guard variable. By default,
+the width is the same as the pointer width.  Currently only supported on AArch64
+targets.  Only the values "4" and "8" are currently supported.  This currently
+only modifies the size of accesses to the global variable, not the value
+stored on the stack.}]>;
 def mstack_protector_guard_symbol_EQ : Joined<["-"], "mstack-protector-guard-symbol=">, Group<m_Group>,
   Visibility<[ClangOption, CC1Option]>,
   HelpText<"Use the given symbol for addressing the stack-protector guard">,

lib/CodeGen/CodeGenModule.cpp

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 416a5be..9ed67d9 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -1716,6 +1716,9 @@
   if (getCodeGenOpts().StackProtectorGuardOffset != INT_MAX)
     getModule().setStackProtectorGuardOffset(
         getCodeGenOpts().StackProtectorGuardOffset);
+  if (getCodeGenOpts().StackProtectorGuardValueWidth != UINT_MAX)
+    getModule().setStackProtectorGuardValueWidth(
+        getCodeGenOpts().StackProtectorGuardValueWidth);
   if (getCodeGenOpts().StackAlignment)
     getModule().setOverrideStackAlignment(getCodeGenOpts().StackAlignment);
   if (getCodeGenOpts().SkipRaxSetup)

lib/Driver/ToolChains/Clang.cpp

diff --git a/lib/Driver/ToolChains/Clang.cpp b/lib/Driver/ToolChains/Clang.cpp
index 92b3045..e411775 100644
--- a/lib/Driver/ToolChains/Clang.cpp
+++ b/lib/Driver/ToolChains/Clang.cpp
@@ -3634,6 +3634,25 @@
     }
     A->render(Args, CmdArgs);
   }
+
+  if (Arg *A =
+          Args.getLastArg(options::OPT_mstack_protector_guard_value_width_EQ)) {
+    if (!EffectiveTriple.isAArch64())
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getAsString(Args) << TripleStr;
+    StringRef Value = A->getValue();
+    unsigned Width;
+    if (Value.getAsInteger(10, Width)) {
+      D.Diag(diag::err_drv_invalid_value) << A->getOption().getName() << Value;
+      return;
+    }
+    if (Width != 4 && Width != 8) {
+      D.Diag(diag::err_drv_invalid_int_value)
+          << A->getOption().getName() << Value;
+      return;
+    }
+    A->render(Args, CmdArgs);
+  }
 }
 
 static void RenderSCPOptions(const ToolChain &TC, const ArgList &Args,

test/CodeGen/stack-protector-guard.c

diff --git a/test/CodeGen/stack-protector-guard.c b/test/CodeGen/stack-protector-guard.c
index 7bffa2a..5438671 100644
--- a/test/CodeGen/stack-protector-guard.c
+++ b/test/CodeGen/stack-protector-guard.c
@@ -27,6 +27,8 @@
 // RUN: %clang_cc1 -mstack-protector-guard=sysreg -triple aarch64-linux-gnu \
 // RUN:   -mstack-protector-guard-offset=1024 -mstack-protector-guard-reg=far_el2 \
 // RUN:   -emit-llvm %s -o - | FileCheck %s --check-prefix=AARCH64 --check-prefix=AARCH64-FAR-EL2
+// RUN: %clang_cc1 -mstack-protector-guard-value-width=4 -triple aarch64-linux-gnu \
+// RUN:   -emit-llvm %s -o - | FileCheck %s --check-prefix=AARCH64-WIDTH-4
 // RUN: %clang_cc1 -mstack-protector-guard=tls -triple riscv64-unknown-elf \
 // RUN:   -mstack-protector-guard-offset=44 -mstack-protector-guard-reg=tp \
 // RUN:   -emit-llvm %s -o - | FileCheck %s --check-prefix=RISCV
@@ -57,6 +59,9 @@
 // AARCH64-FAR-EL2: [[ATTR2]] = !{i32 1, !"stack-protector-guard-reg", !"far_el2"}
 // AARCH64: [[ATTR3]] = !{i32 1, !"stack-protector-guard-offset", i32 1024}
 
+// AARCH64-WIDTH-4: !llvm.module.flags = !{{{.*}}[[ATTR1:![0-9]+]]}
+// AARCH64-WIDTH-4: [[ATTR1]] = !{i32 1, !"stack-protector-guard-value-width", i32 4}
+
 // RISCV: !llvm.module.flags = !{{{.*}}[[ATTR1:![0-9]+]], [[ATTR2:![0-9]+]], [[ATTR3:![0-9]+]], [[ATTR4:![0-9]+]]}
 // RISCV: [[ATTR1]] = !{i32 1, !"stack-protector-guard", !"tls"}
 // RISCV: [[ATTR2]] = !{i32 1, !"stack-protector-guard-reg", !"tp"}