[11,2/5] x86: Add -mharden-sls=[none|all|return|indirect-branch]

diff --git a/gcc/config/i386/i386-opts.h b/gcc/config/i386/i386-opts.h
index de6e7e01661..e159019e904 100644
--- a/gcc/config/i386/i386-opts.h
+++ b/gcc/config/i386/i386-opts.h
@@ -125,4 +125,11 @@  enum instrument_return {
   instrument_return_nop5
 };
 
+enum harden_sls {
+  harden_sls_none = 0,
+  harden_sls_return = 1 << 0,
+  harden_sls_indirect_branch = 1 << 1,
+  harden_sls_all = harden_sls_return | harden_sls_indirect_branch
+};
+
 #endif
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 4ba1a218ee6..f3c4991317d 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -5798,6 +5798,8 @@  output_indirect_thunk (unsigned int regno)
     }
 
   fputs ("\tret\n", asm_out_file);
+  if ((ix86_harden_sls & harden_sls_return))
+    fputs ("\tint3\n", asm_out_file);
 }
 
 /* Output a funtion with a call and return thunk for indirect branch.
@@ -15733,6 +15735,8 @@  ix86_output_jmp_thunk_or_indirect (const char *thunk_name, const int regno)
       fprintf (asm_out_file, "\tjmp\t");
       assemble_name (asm_out_file, thunk_name);
       putc ('\n', asm_out_file);
+      if ((ix86_harden_sls & harden_sls_indirect_branch))
+	fputs ("\tint3\n", asm_out_file);
     }
   else
     output_indirect_thunk (regno);
@@ -15955,10 +15959,10 @@  ix86_output_indirect_jmp (rtx call_op)
 	gcc_unreachable ();
 
       ix86_output_indirect_branch (call_op, "%0", true);
-      return "";
     }
   else
-    return "%!jmp\t%A0";
+    output_asm_insn ("%!jmp\t%A0", &call_op);
+  return (ix86_harden_sls & harden_sls_indirect_branch) ? "int3" : "";
 }
 
 /* Output return instrumentation for current function if needed.  */
@@ -16026,10 +16030,8 @@  ix86_output_function_return (bool long_p)
       return "";
     }
 
-  if (!long_p)
-    return "ret";
-
-  return "rep%; ret";
+  output_asm_insn (long_p ? "rep%; ret" : "ret", nullptr);
+  return (ix86_harden_sls & harden_sls_return) ? "int3" : "";
 }
 
 /* Output indirect function return.  RET_OP is the function return
@@ -16124,7 +16126,12 @@  ix86_output_call_insn (rtx_insn *insn, rtx call_op)
       if (output_indirect_p && !direct_p)
 	ix86_output_indirect_branch (call_op, xasm, true);
       else
-	output_asm_insn (xasm, &call_op);
+	{
+	  output_asm_insn (xasm, &call_op);
+	  if (!direct_p
+	      && (ix86_harden_sls & harden_sls_indirect_branch))
+	    return "int3";
+	}
       return "";
     }
 
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index 7b8547bb1c3..bc401c197b5 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -1113,6 +1113,26 @@  mrecord-return
 Target Var(ix86_flag_record_return) Init(0)
 Generate a __return_loc section pointing to all return instrumentation code.
 
+mharden-sls=
+Target RejectNegative Joined Enum(harden_sls) Var(ix86_harden_sls) Init(harden_sls_none)
+Generate code to mitigate against straight line speculation.
+
+Enum
+Name(harden_sls) Type(enum harden_sls)
+Known choices for mitigation against straight line speculation with -mharden-sls=:
+
+EnumValue
+Enum(harden_sls) String(none) Value(harden_sls_none)
+
+EnumValue
+Enum(harden_sls) String(return) Value(harden_sls_return)
+
+EnumValue
+Enum(harden_sls) String(indirect-branch) Value(harden_sls_indirect_branch)
+
+EnumValue
+Enum(harden_sls) String(all) Value(harden_sls_all)
+
 mavx512bf16
 Target Mask(ISA2_AVX512BF16) Var(ix86_isa_flags2) Save
 Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2, AVX512F and
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 5a4b3c6c234..1fe19800bde 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1409,7 +1409,7 @@  See RS/6000 and PowerPC Options.
 -mstack-protector-guard-symbol=@var{symbol} @gol
 -mgeneral-regs-only  -mcall-ms2sysv-xlogues @gol
 -mindirect-branch=@var{choice}  -mfunction-return=@var{choice} @gol
--mindirect-branch-register -mneeded}
+-mindirect-branch-register -mharden-sls=@var{choice} -mneeded}
 
 @emph{x86 Windows Options}
 @gccoptlist{-mconsole  -mcygwin  -mno-cygwin  -mdll @gol
@@ -31724,6 +31724,14 @@  not be reachable in the large code model.
 @opindex mindirect-branch-register
 Force indirect call and jump via register.
 
+@item -mharden-sls=@var{choice}
+@opindex mharden-sls
+Generate code to mitigate against straight line speculation (SLS) with
+@var{choice}.  The default is @samp{none} which disables all SLS
+hardening.  @samp{return} enables SLS hardening for function return.
+@samp{indirect-branch} enables SLS hardening for indirect branch.
+@samp{all} enables all SLS hardening.
+
 @end table
 
 These @samp{-m} switches are supported in addition to the above
diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-1.c b/gcc/testsuite/gcc.target/i386/harden-sls-1.c
new file mode 100644
index 00000000000..6f70dc94a23
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/harden-sls-1.c
@@ -0,0 +1,14 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mindirect-branch=thunk-extern -mharden-sls=all" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+extern void foo (void);
+
+void
+bar (void)
+{
+  foo ();
+}
+
+/* { dg-final { scan-assembler "jmp\[ \t\]+_?foo" } } */
+/* { dg-final { scan-assembler-not {int3} } } */
diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-2.c b/gcc/testsuite/gcc.target/i386/harden-sls-2.c
new file mode 100644
index 00000000000..a7c59078d03
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/harden-sls-2.c
@@ -0,0 +1,14 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mindirect-branch=thunk-extern -mharden-sls=all" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+extern void (*fptr) (void);
+
+void
+foo (void)
+{
+  fptr ();
+}
+
+/* { dg-final { scan-assembler "jmp\[ \t\]+_?__x86_indirect_thunk_(r|e)ax" } } */
+/* { dg-final { scan-assembler-times "int3" 1 } } */
diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-3.c b/gcc/testsuite/gcc.target/i386/harden-sls-3.c
new file mode 100644
index 00000000000..1a6056b6d7b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/harden-sls-3.c
@@ -0,0 +1,14 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mindirect-branch=thunk -mharden-sls=all" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+extern void (*fptr) (void);
+
+void
+foo (void)
+{
+  fptr ();
+}
+
+/* { dg-final { scan-assembler "jmp\[ \t\]+_?__x86_indirect_thunk_(r|e)ax" } } */
+/* { dg-final { scan-assembler-times "int3" 2 } } */
diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-4.c b/gcc/testsuite/gcc.target/i386/harden-sls-4.c
new file mode 100644
index 00000000000..f70dd1379d3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/harden-sls-4.c
@@ -0,0 +1,16 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mindirect-branch=keep -mharden-sls=all" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+extern void (*fptr) (void);
+
+void
+foo (void)
+{
+  fptr ();
+}
+
+/* { dg-final { scan-assembler "jmp\[ \t\]+\\*_?fptr" { target { ! x32 } } } } */
+/* { dg-final { scan-assembler "movl\[ \t\]+fptr\\(%rip\\), %eax" { target x32 } } } */
+/* { dg-final { scan-assembler "jmp\[ \t\]+\\*%rax" { target x32 } } } */
+/* { dg-final { scan-assembler-times "int3" 1 } } */
diff --git a/gcc/testsuite/gcc.target/i386/harden-sls-5.c b/gcc/testsuite/gcc.target/i386/harden-sls-5.c
new file mode 100644
index 00000000000..613c44c6f82
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/harden-sls-5.c
@@ -0,0 +1,17 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mno-indirect-branch-register -mfunction-return=keep -mindirect-branch=thunk-extern -mharden-sls=return" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+typedef void (*dispatch_t)(long offset);
+
+dispatch_t dispatch;
+
+int
+male_indirect_jump (long offset)
+{
+  dispatch(offset);
+  return 0;
+}
+
+/* { dg-final { scan-assembler-times "ret" 1 } } */
+/* { dg-final { scan-assembler-times "int3" 1 } } */