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.

12 files changed, 159 insertions, 0 deletions

diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-1.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-1.c
new file mode 100644
index 0000000..2463353
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-1.c
@@ -0,0 +1,15 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=skip" } */
+
+volatile int result = 0;
+int 
+__attribute__((noipa))
+foo (int x)
+{
+  return x;
+}
+int main()
+{
+  result = foo (2);
+  return 0;
+}
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c
new file mode 100644
index 0000000..bdaf8e7
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-10.c
@@ -0,0 +1,92 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#include <assert.h>
+int result = 0;
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("skip")))
+foo1 (int x)
+{
+  return (x + 1);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("used-gpr-arg")))
+foo2 (int x)
+{
+  return (x + 2);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("used-gpr")))
+foo3 (int x)
+{
+  return (x + 3);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("used-arg")))
+foo4 (int x)
+{
+  return (x + 4);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("used")))
+foo5 (int x)
+{
+  return (x + 5);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("all-gpr-arg")))
+foo6 (int x)
+{
+  return (x + 6);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("all-gpr")))
+foo7 (int x)
+{
+  return (x + 7);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("all-arg")))
+foo8 (int x)
+{
+  return (x + 8);
+}
+
+int 
+__attribute__((noipa))
+__attribute__ ((zero_call_used_regs("all")))
+foo9 (int x)
+{
+  return (x + 9);
+}
+
+int main()
+{
+  result = foo1 (1);
+  result += foo2 (1);
+  result += foo3 (1);
+  result += foo4 (1);
+  result += foo5 (1);
+  result += foo6 (1);
+  result += foo7 (1);
+  result += foo8 (1);
+  result += foo9 (1);
+  assert (result == 54);
+  return 0;
+}
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c
new file mode 100644
index 0000000..7721e39
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-11.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=all" } */
+
+#include "zero-scratch-regs-10.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-2.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-2.c
new file mode 100644
index 0000000..25891ac
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-2.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=used-gpr-arg" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-3.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-3.c
new file mode 100644
index 0000000..7c3d286
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-3.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=used-gpr" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-4.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-4.c
new file mode 100644
index 0000000..ba28c06
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-4.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=used-arg" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-5.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-5.c
new file mode 100644
index 0000000..26679a4
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-5.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=used" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-6.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-6.c
new file mode 100644
index 0000000..80f5bbb
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-6.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=all-gpr-arg" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-7.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-7.c
new file mode 100644
index 0000000..159f35c
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-7.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=all-gpr" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c
new file mode 100644
index 0000000..c1faaf0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-8.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=all-arg" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c
new file mode 100644
index 0000000..3f14bac
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-9.c
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fzero-call-used-regs=all" } */
+
+#include "zero-scratch-regs-1.c"
diff --git a/gcc/testsuite/c-c++-common/zero-scratch-regs-attr-usages.c b/gcc/testsuite/c-c++-common/zero-scratch-regs-attr-usages.c
new file mode 100644
index 0000000..1e75795
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/zero-scratch-regs-attr-usages.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int result __attribute__ ((zero_call_used_regs("all"))); /* { dg-error "attribute applies only to functions" } */
+int
+__attribute__ ((zero_call_used_regs("gpr-arg-all")))
+foo1 (int x) /* { dg-error "unrecognized 'zero_call_used_regs' attribute argument" } */
+{
+  return (x + 1);
+}
+int
+__attribute__ ((zero_call_used_regs(1)))
+foo2 (int x) /* { dg-error "argument not a string" } */
+{
+  return (x + 2);
+}