Support instrumenting returns of instrumented functions

When instrumenting programs using __fentry__ it is often useful
to instrument the function return too. Traditionally this
has been done by patching the return address on the stack
frame on entry. However this is fairly complicated (trace
function has to emulate a stack) and also slow because
it causes a branch misprediction on every return.

Add an option to generate call or nop instrumentation for
every return instead, including patch sections.

This will increase the program size slightly, but can be a
lot faster and simpler.

This version only instruments true returns, not sibling
calls or tail recursion. This matches the semantics of the
original stack.

gcc/:

2018-11-29  Andi Kleen  <ak@linux.intel.com>

	* config/i386/i386-opts.h (enum instrument_return): Add.
	* config/i386/i386.c (output_return_instrumentation): Add.
	(ix86_output_function_return): Call output_return_instrumentation.
	(ix86_output_call_insn): Call output_return_instrumentation.
	* config/i386/i386.opt: Add -minstrument-return=.
	* doc/invoke.texi (-minstrument-return): Document.

gcc/testsuite/:

2018-11-29  Andi Kleen  <ak@linux.intel.com>

	* gcc.target/i386/returninst1.c: New test.
	* gcc.target/i386/returninst2.c: New test.
	* gcc.target/i386/returninst3.c: New test.

From-SVN: r266652

gcc/ChangeLog

@@ -1,3 +1,12 @@
+2018-11-29  Andi Kleen  <ak@linux.intel.com>
+
+	* config/i386/i386-opts.h (enum instrument_return): Add.
+	* config/i386/i386.c (output_return_instrumentation): Add.
+	(ix86_output_function_return): Call output_return_instrumentation.
+	(ix86_output_call_insn): Call output_return_instrumentation.
+	* config/i386/i386.opt: Add -minstrument-return=.
+	* doc/invoke.texi (-minstrument-return): Document.
+
 2018-11-29  Eric Botcazou  <ebotcazou@adacore.com>
 
 	PR target/87807

gcc/config/i386/i386-opts.h

@@ -119,4 +119,10 @@ enum indirect_branch {
   indirect_branch_thunk_extern
 };
 
+enum instrument_return {
+  instrument_return_none = 0,
+  instrument_return_call,
+  instrument_return_nop5
+};
+
 #endif

gcc/config/i386/i386.c

@@ -28385,12 +28385,47 @@ ix86_output_indirect_jmp (rtx call_op)
     return "%!jmp\t%A0";
 }
 
+/* Output return instrumentation for current function if needed.  */
+
+static void
+output_return_instrumentation (void)
+{
+  if (ix86_instrument_return != instrument_return_none
+      && flag_fentry
+      && !DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT (cfun->decl))
+    {
+      if (ix86_flag_record_return)
+	fprintf (asm_out_file, "1:\n");
+      switch (ix86_instrument_return)
+	{
+	case instrument_return_call:
+	  fprintf (asm_out_file, "\tcall\t__return__\n");
+	  break;
+	case instrument_return_nop5:
+	  /* 5 byte nop: nopl 0(%[re]ax,%[re]ax,1)  */
+	  fprintf (asm_out_file, ASM_BYTE "0x0f, 0x1f, 0x44, 0x00, 0x00\n");
+	  break;
+	case instrument_return_none:
+	  break;
+	}
+
+      if (ix86_flag_record_return)
+	{
+	  fprintf (asm_out_file, "\t.section __return_loc, \"a\",@progbits\n");
+	  fprintf (asm_out_file, "\t.%s 1b\n", TARGET_64BIT ? "quad" : "long");
+	  fprintf (asm_out_file, "\t.previous\n");
+	}
+    }
+}
+
 /* Output function return.  CALL_OP is the jump target.  Add a REP
    prefix to RET if LONG_P is true and function return is kept.  */
 
 const char *
 ix86_output_function_return (bool long_p)
 {
+  output_return_instrumentation ();
+
   if (cfun->machine->function_return_type != indirect_branch_keep)
     {
       char thunk_name[32];
@@ -28503,6 +28538,7 @@ ix86_output_call_insn (rtx_insn *insn, rtx call_op)
 
   if (SIBLING_CALL_P (insn))
     {
+      output_return_instrumentation ();
       if (direct_p)
 	{
 	  if (ix86_nopic_noplt_attribute_p (call_op))

gcc/config/i386/i386.opt

@@ -1067,3 +1067,24 @@ Support WAITPKG built-in functions and code generation.
 mcldemote
 Target Report Mask(ISA_CLDEMOTE) Var(ix86_isa_flags2) Save
 Support CLDEMOTE built-in functions and code generation.
+
+minstrument-return=
+Target Report RejectNegative Joined Enum(instrument_return) Var(ix86_instrument_return) Init(instrument_return_none)
+Instrument function exit in instrumented functions with __fentry__.
+
+Enum
+Name(instrument_return) Type(enum instrument_return)
+Known choices for return instrumentation with -minstrument-return=
+
+EnumValue
+Enum(instrument_return) String(none) Value(instrument_return_none)
+
+EnumValue
+Enum(instrument_return) String(call) Value(instrument_return_call)
+
+EnumValue
+Enum(instrument_return) String(nop5) Value(instrument_return_nop5)
+
+mrecord-return
+Target Report Var(ix86_flag_record_return) Init(0)
+Generate a __return_loc section pointing to all return instrumentation code.

gcc/doc/invoke.texi

@@ -1316,6 +1316,7 @@ See RS/6000 and PowerPC Options.
 -mcmodel=@var{code-model}  -mabi=@var{name}  -maddress-mode=@var{mode} @gol
 -m32  -m64  -mx32  -m16  -miamcu  -mlarge-data-threshold=@var{num} @gol
 -msse2avx  -mfentry  -mrecord-mcount  -mnop-mcount  -m8bit-idiv @gol
+-minstrument-return=@var{type} @gol
 -mavx256-split-unaligned-load  -mavx256-split-unaligned-store @gol
 -malign-data=@var{type}  -mstack-protector-guard=@var{guard} @gol
 -mstack-protector-guard-reg=@var{reg} @gol
@@ -29077,6 +29078,19 @@ the profiling functions as NOPs. This is useful when they
 should be patched in later dynamically. This is likely only
 useful together with @option{-mrecord-mcount}.
 
+@item -minstrument-return=@var{type}
+@opindex minstrument-return
+Instrument function exit in -pg -mfentry instrumented functions with
+call to specified function. This only instruments true returns ending
+with ret, but not sibling calls ending with jump. Valid types
+are @var{none} to not instrument, @var{call} to generate a call to __return__,
+or @var{nop5} to generate a 5 byte nop.
+
+@item -mrecord-return
+@itemx -mno-record-return
+@opindex mrecord-return
+Generate a __return_loc section pointing to all return instrumentation code.
+
 @item -mskip-rax-setup
 @itemx -mno-skip-rax-setup
 @opindex mskip-rax-setup

gcc/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2018-11-29  Andi Kleen  <ak@linux.intel.com>
+
+	* gcc.target/i386/returninst1.c: New test.
+	* gcc.target/i386/returninst2.c: New test.
+	* gcc.target/i386/returninst3.c: New test.
+
 2018-11-29  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gcc.target/sparc/20181129-1.c: New test.

gcc/testsuite/gcc.target/i386/returninst1.c

@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-pg -mfentry -minstrument-return=call -mrecord-return" } */
+/* { dg-final { scan-assembler "call.*__return__" } } */
+/* { dg-final { scan-assembler "section.*return_loc" } } */
+
+int func(int a)
+{
+  return a+1;
+}
+
+int func2(int a)
+{
+  return a+1;
+}

gcc/testsuite/gcc.target/i386/returninst2.c

@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-pg -mfentry -minstrument-return=nop5 -mrecord-return" } */
+/* { dg-final { scan-assembler-times "0x0f, 0x1f, 0x44, 0x00, 0x00" 3 } } */
+/* { dg-final { scan-assembler "section.*return_loc" } } */
+
+int func(int a)
+{
+  return a+1;
+}
+
+int func2(int a)
+{
+  return a+1;
+}
+
+extern void func4(int);
+
+int func3(int a)
+{
+  func4(a + 1);
+}

gcc/testsuite/gcc.target/i386/returninst3.c

@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-pg -mfentry -minstrument-return=call" } */
+/* { dg-final { scan-assembler-not "call.*__return__" } } */
+
+__attribute__((no_instrument_function))
+int func(int a)
+{
+  return a+1;
+}