Add -fzero-call-used-regs option and zero_call_used_regs function attributes.

This new feature causes the compiler to zero a  subset of all call-used
registers at function return.  This is used to increase program security
by either mitigating Return-Oriented Programming (ROP) attacks or
preventing information leakage through registers.

gcc/ChangeLog:

2020-10-30  Qing Zhao  <qing.zhao@oracle.com>
	    H.J.Lu  <hjl.tools@gmail.com>

	* common.opt: Add new option -fzero-call-used-regs
	* config/i386/i386.c (zero_call_used_regno_p): New function.
	(zero_call_used_regno_mode): Likewise.
	(zero_all_vector_registers): Likewise.
	(zero_all_st_registers): Likewise.
	(zero_all_mm_registers): Likewise.
	(ix86_zero_call_used_regs): Likewise.
	(TARGET_ZERO_CALL_USED_REGS): Define.
	* df-scan.c (df_epilogue_uses_p): New function.
	(df_get_exit_block_use_set): Replace EPILOGUE_USES with
	df_epilogue_uses_p.
	* df.h (df_epilogue_uses_p): Declare.
	* doc/extend.texi: Document the new zero_call_used_regs attribute.
	* doc/invoke.texi: Document the new -fzero-call-used-regs option.
	* doc/tm.texi: Regenerate.
	* doc/tm.texi.in (TARGET_ZERO_CALL_USED_REGS): New hook.
	* emit-rtl.h (struct rtl_data): New field must_be_zero_on_return.
	* flag-types.h (namespace zero_regs_flags): New namespace.
	* function.c (gen_call_used_regs_seq): New function.
	(class pass_zero_call_used_regs): New class.
	(pass_zero_call_used_regs::execute): New function.
	(make_pass_zero_call_used_regs): New function.
	* optabs.c (expand_asm_reg_clobber_mem_blockage): New function.
	* optabs.h (expand_asm_reg_clobber_mem_blockage): Declare.
	* opts.c (zero_call_used_regs_opts): New structure array
	initialization.
	(parse_zero_call_used_regs_options): New function.
	(common_handle_option): Handle -fzero-call-used-regs.
	* opts.h (zero_call_used_regs_opts): New structure array.
	* passes.def: Add new pass pass_zero_call_used_regs.
	* recog.c (valid_insn_p): New function.
	* recog.h (valid_insn_p): Declare.
	* resource.c (init_resource_info): Replace EPILOGUE_USES with
	df_epilogue_uses_p.
	* target.def (zero_call_used_regs): New hook.
	* targhooks.c (default_zero_call_used_regs): New function.
	* targhooks.h (default_zero_call_used_regs): Declare.
	* tree-pass.h (make_pass_zero_call_used_regs): Declare.

gcc/c-family/ChangeLog:

2020-10-30  Qing Zhao  <qing.zhao@oracle.com>
	    H.J.Lu  <hjl.tools@gmail.com>

	* c-attribs.c (c_common_attribute_table): Add new attribute
	zero_call_used_regs.
	(handle_zero_call_used_regs_attribute): New function.

gcc/testsuite/ChangeLog:

2020-10-30  Qing Zhao  <qing.zhao@oracle.com>
	    H.J.Lu  <hjl.tools@gmail.com>

	* c-c++-common/zero-scratch-regs-1.c: New test.
	* c-c++-common/zero-scratch-regs-10.c: New test.
	* c-c++-common/zero-scratch-regs-11.c: New test.
	* c-c++-common/zero-scratch-regs-2.c: New test.
	* c-c++-common/zero-scratch-regs-3.c: New test.
	* c-c++-common/zero-scratch-regs-4.c: New test.
	* c-c++-common/zero-scratch-regs-5.c: New test.
	* c-c++-common/zero-scratch-regs-6.c: New test.
	* c-c++-common/zero-scratch-regs-7.c: New test.
	* c-c++-common/zero-scratch-regs-8.c: New test.
	* c-c++-common/zero-scratch-regs-9.c: New test.
	* c-c++-common/zero-scratch-regs-attr-usages.c: New test.
	* gcc.target/i386/zero-scratch-regs-1.c: New test.
	* gcc.target/i386/zero-scratch-regs-10.c: New test.
	* gcc.target/i386/zero-scratch-regs-11.c: New test.
	* gcc.target/i386/zero-scratch-regs-12.c: New test.
	* gcc.target/i386/zero-scratch-regs-13.c: New test.
	* gcc.target/i386/zero-scratch-regs-14.c: New test.
	* gcc.target/i386/zero-scratch-regs-15.c: New test.
	* gcc.target/i386/zero-scratch-regs-16.c: New test.
	* gcc.target/i386/zero-scratch-regs-17.c: New test.
	* gcc.target/i386/zero-scratch-regs-18.c: New test.
	* gcc.target/i386/zero-scratch-regs-19.c: New test.
	* gcc.target/i386/zero-scratch-regs-2.c: New test.
	* gcc.target/i386/zero-scratch-regs-20.c: New test.
	* gcc.target/i386/zero-scratch-regs-21.c: New test.
	* gcc.target/i386/zero-scratch-regs-22.c: New test.
	* gcc.target/i386/zero-scratch-regs-23.c: New test.
	* gcc.target/i386/zero-scratch-regs-24.c: New test.
	* gcc.target/i386/zero-scratch-regs-25.c: New test.
	* gcc.target/i386/zero-scratch-regs-26.c: New test.
	* gcc.target/i386/zero-scratch-regs-27.c: New test.
	* gcc.target/i386/zero-scratch-regs-28.c: New test.
	* gcc.target/i386/zero-scratch-regs-29.c: New test.
	* gcc.target/i386/zero-scratch-regs-30.c: New test.
	* gcc.target/i386/zero-scratch-regs-31.c: New test.
	* gcc.target/i386/zero-scratch-regs-3.c: New test.
	* gcc.target/i386/zero-scratch-regs-4.c: New test.
	* gcc.target/i386/zero-scratch-regs-5.c: New test.
	* gcc.target/i386/zero-scratch-regs-6.c: New test.
	* gcc.target/i386/zero-scratch-regs-7.c: New test.
	* gcc.target/i386/zero-scratch-regs-8.c: New test.
	* gcc.target/i386/zero-scratch-regs-9.c: New test.

1 files changed, 32 insertions, 0 deletions

diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index 5d94fce..4e4d100 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -56,6 +56,9 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-ssa-alias.h"
 #include "gimple-expr.h"
 #include "memmodel.h"
+#include "backend.h"
+#include "emit-rtl.h"
+#include "df.h"
 #include "tm_p.h"
 #include "stringpool.h"
 #include "tree-vrp.h"
@@ -987,6 +990,35 @@ default_function_value_regno_p (const unsigned int regno ATTRIBUTE_UNUSED)
 #endif
 }
 
+/* The default hook for TARGET_ZERO_CALL_USED_REGS.  */
+
+HARD_REG_SET
+default_zero_call_used_regs (HARD_REG_SET need_zeroed_hardregs)
+{
+  gcc_assert (!hard_reg_set_empty_p (need_zeroed_hardregs));
+
+  for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
+    if (TEST_HARD_REG_BIT (need_zeroed_hardregs, regno))
+      {
+	rtx_insn *last_insn = get_last_insn ();
+	machine_mode mode = GET_MODE (regno_reg_rtx[regno]);
+	rtx zero = CONST0_RTX (mode);
+	rtx_insn *insn = emit_move_insn (regno_reg_rtx[regno], zero);
+	if (!valid_insn_p (insn))
+	  {
+	    static bool issued_error;
+	    if (!issued_error)
+	      {
+		issued_error = true;
+		sorry ("%qs not supported on this target",
+			"-fzero-call-used_regs");
+	      }
+	    delete_insns_since (last_insn);
+	  }
+      }
+  return need_zeroed_hardregs;
+}
+
 rtx
 default_internal_arg_pointer (void)
 {