[ARM] Implement execute-only support in CodeGen
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.
llvm-svn: 289784
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.h b/llvm/lib/Target/ARM/ARMSubtarget.h
index c3a355b..8c8218d 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.h
+++ b/llvm/lib/Target/ARM/ARMSubtarget.h
@@ -301,6 +301,9 @@
/// Generate calls via indirect call instructions.
bool GenLongCalls = false;
+ /// Generate code that does not contain data access to code sections.
+ bool GenExecuteOnly = false;
+
/// Target machine allowed unsafe FP math (such as use of NEON fp)
bool UnsafeFPMath = false;
@@ -494,6 +497,7 @@
bool useNaClTrap() const { return UseNaClTrap; }
bool useSjLjEH() const { return UseSjLjEH; }
bool genLongCalls() const { return GenLongCalls; }
+ bool genExecuteOnly() const { return GenExecuteOnly; }
bool hasFP16() const { return HasFP16; }
bool hasD16() const { return HasD16; }