[ARM] Implement execute-only support in CodeGen

Summary:
This implements execute-only support for ARM code generation, which
prevents the compiler from generating data accesses to code sections.
The following changes are involved:

* Add the CodeGen option "-arm-execute-only" to the ARM code generator.
* Add the clang flag "-mexecute-only" as well as the GCC-compatible
  alias "-mpure-code" to enable this option.
* When enabled, literal pools are replaced with MOVW/MOVT instructions,
  with VMOV used in addition for floating-point literals. As the MOVT
  instruction is required, execute-only support is only available in
  Thumb mode for targets supporting ARMv8-M baseline or Thumb2.
* Jump tables are placed in data sections when in execute-only mode.
* The execute-only text section is assigned section ID 0, and is
  marked as unreadable with the SHF_ARM_PURECODE flag with symbol 'y'.
  This also overrides selection of ELF sections for globals.

Reviewers: t.p.northover, rengolin

Subscribers: llvm-commits, aemerson

Differential Revision: https://reviews.llvm.org/D27450

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@289786 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 131 insertions, 1 deletions

diff --git a/include/clang/Basic/DiagnosticCommonKinds.td b/include/clang/Basic/DiagnosticCommonKinds.td
index adc74d9619..e8180eb1db 100644
--- a/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/include/clang/Basic/DiagnosticCommonKinds.td
@@ -190,6 +190,8 @@ def err_target_unsupported_fpmath : Error<
     "the '%0' unit is not supported with this instruction set">;
 def err_target_unsupported_unaligned : Error<
   "the %0 sub-architecture does not support unaligned accesses">;
+def err_target_unsupported_execute_only : Error<
+  "execute only is not supported for the %0 sub-architecture">;
 def err_opt_not_valid_with_opt : Error<
   "option '%0' cannot be specified with '%1'">;
 
diff --git a/include/clang/Driver/Options.td b/include/clang/Driver/Options.td
index 74f0c2a9df..35e15ed866 100644
--- a/include/clang/Driver/Options.td
+++ b/include/clang/Driver/Options.td
@@ -1455,6 +1455,12 @@ def mlong_calls : Flag<["-"], "mlong-calls">, Group<m_Group>,
   HelpText<"Generate branches with extended addressability, usually via indirect jumps.">;
 def mno_long_calls : Flag<["-"], "mno-long-calls">, Group<m_Group>,
   HelpText<"Restore the default behaviour of not generating long calls">;
+def mexecute_only : Flag<["-"], "mexecute-only">, Group<m_arm_Features_Group>,
+  HelpText<"Disallow generation of data access to code sections (ARM only)">;
+def mno_execute_only : Flag<["-"], "mno-execute-only">, Group<m_arm_Features_Group>,
+  HelpText<"Allow generation of data access to code sections (ARM only)">;
+def mpure_code : Flag<["-"], "mpure-code">, Alias<mexecute_only>; // Alias for GCC compatibility
+def mno_pure_code : Flag<["-"], "mno-pure-code">, Alias<mno_execute_only>;
 def mtvos_version_min_EQ : Joined<["-"], "mtvos-version-min=">, Group<m_Group>;
 def mappletvos_version_min_EQ : Joined<["-"], "mappletvos-version-min=">, Alias<mtvos_version_min_EQ>;
 def mtvos_simulator_version_min_EQ : Joined<["-"], "mtvos-simulator-version-min=">, Alias<mtvos_version_min_EQ>;
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 3b20805c88..8f1f341c7b 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1001,6 +1001,7 @@ arm::FloatABI arm::getARMFloatABI(const ToolChain &TC, const ArgList &Args) {
 static void getARMTargetFeatures(const ToolChain &TC,
                                  const llvm::Triple &Triple,
                                  const ArgList &Args,
+                                 ArgStringList &CmdArgs,
                                  std::vector<StringRef> &Features,
                                  bool ForAS) {
   const Driver &D = TC.getDriver();
@@ -1139,6 +1140,28 @@ static void getARMTargetFeatures(const ToolChain &TC,
       Features.push_back("+long-calls");
   }
 
+  // Generate execute-only output (no data access to code sections).
+  // Supported only on ARMv6T2 and ARMv7 and above.
+  // Cannot be combined with -mno-movt or -mlong-calls
+  if (Arg *A = Args.getLastArg(options::OPT_mexecute_only, options::OPT_mno_execute_only)) {
+    if (A->getOption().matches(options::OPT_mexecute_only)) {
+      if (getARMSubArchVersionNumber(Triple) < 7 &&
+          llvm::ARM::parseArch(Triple.getArchName()) != llvm::ARM::AK_ARMV6T2)
+            D.Diag(diag::err_target_unsupported_execute_only) << Triple.getArchName();
+      else if (Arg *B = Args.getLastArg(options::OPT_mno_movt))
+        D.Diag(diag::err_opt_not_valid_with_opt) << A->getAsString(Args) << B->getAsString(Args);
+      // Long calls create constant pool entries and have not yet been fixed up
+      // to play nicely with execute-only. Hence, they cannot be used in
+      // execute-only code for now
+      else if (Arg *B = Args.getLastArg(options::OPT_mlong_calls, options::OPT_mno_long_calls)) {
+        if (B->getOption().matches(options::OPT_mlong_calls))
+          D.Diag(diag::err_opt_not_valid_with_opt) << A->getAsString(Args) << B->getAsString(Args);
+      }
+
+      CmdArgs.push_back("-arm-execute-only");
+    }
+  }
+
   // Kernel code has more strict alignment requirements.
   if (KernelOrKext)
     Features.push_back("+strict-align");
@@ -2703,7 +2726,7 @@ static void getTargetFeatures(const ToolChain &TC, const llvm::Triple &Triple,
   case llvm::Triple::armeb:
   case llvm::Triple::thumb:
   case llvm::Triple::thumbeb:
-    getARMTargetFeatures(TC, Triple, Args, Features, ForAS);
+    getARMTargetFeatures(TC, Triple, Args, CmdArgs, Features, ForAS);
     break;
 
   case llvm::Triple::ppc:
diff --git a/test/Driver/arm-execute-only.c b/test/Driver/arm-execute-only.c
new file mode 100644
index 0000000000..f564594b83
--- /dev/null
+++ b/test/Driver/arm-execute-only.c
@@ -0,0 +1,99 @@
+// RUN: %clang -target armv6t2-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv6t2-eabi -### -mexecute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv6t2-eabi -### -mexecute-only -mno-execute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv7m-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv7m-eabi -### -mexecute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv7m-eabi -### -mexecute-only -mno-execute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.base-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.base-eabi -### -mexecute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.base-eabi -### -mexecute-only -mno-execute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.main-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.main-eabi -### -mexecute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.main-eabi -### -mexecute-only -mno-execute-only %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: not %clang -c -target thumbv6m-eabi -mexecute-only %s 2>&1 | \
+// RUN:   FileCheck --check-prefix CHECK-EXECUTE-ONLY-NOT-SUPPORTED %s
+
+// RUN: not %clang -target armv8m.main-eabi -mexecute-only -mno-movt %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY-NO-MOVT
+
+// RUN: not %clang -target armv8m.main-eabi -mexecute-only -mlong-calls %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY-LONG-CALLS
+
+
+// -mpure-code flag for GCC compatibility
+// RUN: %clang -target armv6t2-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv6t2-eabi -### -mpure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv6t2-eabi -### -mpure-code -mno-pure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv7m-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv7m-eabi -### -mpure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv7m-eabi -### -mpure-code -mno-pure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.base-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.base-eabi -### -mpure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.base-eabi -### -mpure-code -mno-pure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.main-eabi -### %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.main-eabi -### -mpure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY
+
+// RUN: %clang -target armv8m.main-eabi -### -mpure-code -mno-pure-code %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-NO-EXECUTE-ONLY
+
+// RUN: not %clang -c -target thumbv6m-eabi -mpure-code %s 2>&1 | \
+// RUN:   FileCheck --check-prefix CHECK-EXECUTE-ONLY-NOT-SUPPORTED %s
+
+// RUN: not %clang -target armv8m.main-eabi -mpure-code -mno-movt %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY-NO-MOVT
+
+// RUN: not %clang -target armv8m.main-eabi -mpure-code -mlong-calls %s 2>&1 \
+// RUN:    | FileCheck %s -check-prefix CHECK-EXECUTE-ONLY-LONG-CALLS
+
+//
+// CHECK-NO-EXECUTE-ONLY-NOT: "-arm-execute-only"
+// CHECK-EXECUTE-ONLY: "-arm-execute-only"
+
+// CHECK-EXECUTE-ONLY-NOT-SUPPORTED: error: execute only is not supported for the thumbv6m sub-architecture
+// CHECK-EXECUTE-ONLY-NO-MOVT: error: option '-mexecute-only' cannot be specified with '-mno-movt'
+// CHECK-EXECUTE-ONLY-LONG-CALLS: error: option '-mexecute-only' cannot be specified with '-mlong-calls'