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, 42 insertions, 0 deletions

diff --git a/gcc/optabs.c b/gcc/optabs.c
index 8ad7f4b..1820b91 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -6484,6 +6484,48 @@ expand_memory_blockage (void)
     expand_asm_memory_blockage ();
 }
 
+/* Generate asm volatile("" : : : "memory") as a memory blockage, at the
+   same time clobbering the register set specified by REGS.  */
+
+void
+expand_asm_reg_clobber_mem_blockage (HARD_REG_SET regs)
+{
+  rtx asm_op, clob_mem;
+
+  unsigned int num_of_regs = 0;
+  for (unsigned int i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    if (TEST_HARD_REG_BIT (regs, i))
+      num_of_regs++;
+
+  asm_op = gen_rtx_ASM_OPERANDS (VOIDmode, "", "", 0,
+				 rtvec_alloc (0), rtvec_alloc (0),
+				 rtvec_alloc (0), UNKNOWN_LOCATION);
+  MEM_VOLATILE_P (asm_op) = 1;
+
+  rtvec v = rtvec_alloc (num_of_regs + 2);
+
+  clob_mem = gen_rtx_SCRATCH (VOIDmode);
+  clob_mem = gen_rtx_MEM (BLKmode, clob_mem);
+  clob_mem = gen_rtx_CLOBBER (VOIDmode, clob_mem);
+
+  RTVEC_ELT (v, 0) = asm_op;
+  RTVEC_ELT (v, 1) = clob_mem;
+
+  if (num_of_regs > 0)
+    {
+      unsigned int j = 2;
+      for (unsigned int i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+	if (TEST_HARD_REG_BIT (regs, i))
+	  {
+	    RTVEC_ELT (v, j) = gen_rtx_CLOBBER (VOIDmode, regno_reg_rtx[i]);
+ 	    j++;
+	  }
+      gcc_assert (j == (num_of_regs + 2));
+    }
+
+  emit_insn (gen_rtx_PARALLEL (VOIDmode, v));
+}
+
 /* This routine will either emit the mem_thread_fence pattern or issue a 
    sync_synchronize to generate a fence for memory model MEMMODEL.  */