[PATCH v2] x86: Add -mindirect-branch-cs-prefix

[H.J. Lu]

Add -mindirect-branch-cs-prefix to add CS prefix to call and jmp to thunk
via r8-r15 registers when converting indirect call and jump to increase
the instruction length to 6, allowing the non-thunk form to be inlined.

gcc/

	PR target/102952
	* config/i386/i386.c (ix86_output_jmp_thunk_or_indirect): Emit
	CS prefix for -mindirect-branch-cs-prefix.
	(ix86_output_indirect_branch_via_reg): Likewise.
	* config/i386/i386.opt: Add -mindirect-branch-cs-prefix.
	* doc/invoke.texi: Document -mindirect-branch-cs-prefix.

gcc/testsuite/

	PR target/102952
	* gcc.target/i386/indirect-thunk-cs-prefix-1.c: New test.
	* gcc.target/i386/indirect-thunk-cs-prefix-2.c: Likewise.
---
 gcc/config/i386/i386.c                            |  6 ++++++
 gcc/config/i386/i386.opt                          |  4 ++++
 gcc/doc/invoke.texi                               |  8 +++++++-
 .../gcc.target/i386/indirect-thunk-cs-prefix-1.c  | 14 ++++++++++++++
 .../gcc.target/i386/indirect-thunk-cs-prefix-2.c  | 15 +++++++++++++++
 5 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c
 create mode 100644 gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 7e9b7bc347f..ae92df0be2f 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -15983,6 +15983,9 @@ ix86_output_jmp_thunk_or_indirect (const char *thunk_name, const int regno)
 {
   if (thunk_name != NULL)
     {
+      if (REX_INT_REGNO_P (regno)
+	  && ix86_indirect_branch_cs_prefix)
+	fprintf (asm_out_file, "\tcs\n");
       fprintf (asm_out_file, "\tjmp\t");
       assemble_name (asm_out_file, thunk_name);
       putc ('\n', asm_out_file);
@@ -16036,6 +16039,9 @@ ix86_output_indirect_branch_via_reg (rtx call_op, bool sibcall_p)
     {
       if (thunk_name != NULL)
 	{
+	  if (REX_INT_REGNO_P (regno)
+	      && ix86_indirect_branch_cs_prefix)
+	    fprintf (asm_out_file, "\tcs\n");
 	  fprintf (asm_out_file, "\tcall\t");
 	  assemble_name (asm_out_file, thunk_name);
 	  putc ('\n', asm_out_file);
diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
index 8d499a5a4df..806ffd7b0ac 100644
--- a/gcc/config/i386/i386.opt
+++ b/gcc/config/i386/i386.opt
@@ -1076,6 +1076,10 @@ Enum(indirect_branch) String(thunk-inline) Value(indirect_branch_thunk_inline)
 EnumValue
 Enum(indirect_branch) String(thunk-extern) Value(indirect_branch_thunk_extern)
 
+mindirect-branch-cs-prefix
+Target Var(ix86_indirect_branch_cs_prefix) Init(0)
+Add CS prefix to call and jmp to thunk via r8-r15 registers when converting indirect call and jump.
+
 mindirect-branch-register
 Target Var(ix86_indirect_branch_register) Init(0)
 Force indirect call and jump via register.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 0265c160e02..233f3b579d9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1427,7 +1427,8 @@ See RS/6000 and PowerPC Options.
 -mstack-protector-guard-symbol=@var{symbol} @gol
 -mgeneral-regs-only  -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop @gol
 -mindirect-branch=@var{choice}  -mfunction-return=@var{choice} @gol
--mindirect-branch-register -mharden-sls=@var{choice} -mneeded}
+-mindirect-branch-register -mharden-sls=@var{choice} @gol
+-mindirect-branch-cs-prefix -mneeded}
 
 @emph{x86 Windows Options}
 @gccoptlist{-mconsole  -mcygwin  -mno-cygwin  -mdll @gol
@@ -32409,6 +32410,11 @@ hardening.  @samp{return} enables SLS hardening for function return.
 @samp{indirect-branch} enables SLS hardening for indirect branch.
 @samp{all} enables all SLS hardening.
 
+@item -mindirect-branch-cs-prefix
+@opindex mindirect-branch-cs-prefix
+Add CS prefix to call and jmp to thunk via r8-r15 registers when
+converting indirect call and jump.
+
 @end table
 
 These @samp{-m} switches are supported in addition to the above
diff --git a/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c
new file mode 100644
index 00000000000..db2f3416823
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2 -ffixed-rax -ffixed-rbx -ffixed-rcx -ffixed-rdx -ffixed-rdi -ffixed-rsi -mindirect-branch-cs-prefix -mindirect-branch=thunk-extern" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+extern void (*fptr) (void);
+
+void
+foo (void)
+{
+  fptr ();
+}
+
+/* { dg-final { scan-assembler-times "jmp\[ \t\]+_?__x86_indirect_thunk_r\[0-9\]+" 1 } } */
+/* { dg-final { scan-assembler-times "\tcs" 1 } } */
diff --git a/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c
new file mode 100644
index 00000000000..adfc39a49d4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/indirect-thunk-cs-prefix-2.c
@@ -0,0 +1,15 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-O2 -ffixed-rax -ffixed-rbx -ffixed-rcx -ffixed-rdx -ffixed-rdi -ffixed-rsi -mindirect-branch-cs-prefix -mindirect-branch=thunk-extern" } */
+/* { dg-additional-options "-fno-pic" { target { ! *-*-darwin* } } } */
+
+extern void (*bar) (void);
+
+int
+foo (void)
+{
+  bar ();
+  return 0;
+}
+
+/* { dg-final { scan-assembler-times "call\[ \t\]+_?__x86_indirect_thunk_r\[0-9\]+" 1 } } */
+/* { dg-final { scan-assembler-times "\tcs" 1 } } */
-- 
2.33.1