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, 44 insertions, 0 deletions

diff --git a/gcc/opts.c b/gcc/opts.c
index da503c3..96291e8 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -1776,6 +1776,24 @@ const struct sanitizer_opts_s coverage_sanitizer_opts[] =
   { NULL, 0U, 0UL, false }
 };
 
+/* -fzero-call-used-regs= suboptions.  */
+const struct zero_call_used_regs_opts_s zero_call_used_regs_opts[] =
+{
+#define ZERO_CALL_USED_REGS_OPT(name, flags) \
+    { #name, flags }
+  ZERO_CALL_USED_REGS_OPT (skip, zero_regs_flags::SKIP),
+  ZERO_CALL_USED_REGS_OPT (used-gpr-arg, zero_regs_flags::USED_GPR_ARG),
+  ZERO_CALL_USED_REGS_OPT (used-gpr, zero_regs_flags::USED_GPR),
+  ZERO_CALL_USED_REGS_OPT (used-arg, zero_regs_flags::USED_ARG),
+  ZERO_CALL_USED_REGS_OPT (used, zero_regs_flags::USED),
+  ZERO_CALL_USED_REGS_OPT (all-gpr-arg, zero_regs_flags::ALL_GPR_ARG),
+  ZERO_CALL_USED_REGS_OPT (all-gpr, zero_regs_flags::ALL_GPR),
+  ZERO_CALL_USED_REGS_OPT (all-arg, zero_regs_flags::ALL_ARG),
+  ZERO_CALL_USED_REGS_OPT (all, zero_regs_flags::ALL),
+#undef ZERO_CALL_USED_REGS_OPT
+  {NULL, 0U}
+};
+
 /* A struct for describing a run of chars within a string.  */
 
 class string_fragment
@@ -1970,6 +1988,27 @@ parse_no_sanitize_attribute (char *value)
   return flags;
 }
 
+/* Parse -fzero-call-used-regs suboptions from ARG, return the FLAGS.  */
+
+unsigned int
+parse_zero_call_used_regs_options (const char *arg)
+{
+  unsigned int flags = 0;
+
+  /* Check to see if the string matches a sub-option name.  */
+  for (unsigned int i = 0; zero_call_used_regs_opts[i].name != NULL; ++i)
+    if (strcmp (arg, zero_call_used_regs_opts[i].name) == 0)
+      {
+	flags = zero_call_used_regs_opts[i].flag;
+	break;
+      }
+
+  if (!flags)
+    error ("unrecognized argument to %<-fzero-call-used-regs=%>: %qs", arg);
+
+  return flags;
+}
+
 /* Parse -falign-NAME format for a FLAG value.  Return individual
    parsed integer values into RESULT_VALUES array.  If REPORT_ERROR is
    set, print error message at LOC location.  */
@@ -2596,6 +2635,11 @@ common_handle_option (struct gcc_options *opts,
       /* Automatically sets -ftree-loop-vectorize and
 	 -ftree-slp-vectorize.  Nothing more to do here.  */
       break;
+    case OPT_fzero_call_used_regs_:
+      opts->x_flag_zero_call_used_regs
+	= parse_zero_call_used_regs_options (arg);
+      break;
+
     case OPT_fshow_column:
       dc->show_column = value;
       break;