Hello!
Attached patch prevents red-zone with -fPIC for leaf functions on
i686. The idea is to mark when set_got is expanded as a call to a pc
thunk, and use this flag to prevent red-zone in the current function.
Please note that using red-zone with i686 violates all known ABIs, but
some future ABI can trip on this limitation. The failure mode is quite
tricky, so IMO it warrants a couple of lines as a safety net.
The testcase is not suitable for the testsuite (it uses -mred-zone for
i686 target), but I have checked that the testcase works OK when
compiled with the patched compiler even when -mred-zone is used
together with -fPIC.
Jakub, HJ - what do you think?
2016-03-01 Uros Bizjak <ubiz...@gmail.com>
PR target/70064
* config/i386/i386.h (machine_function): Add
pc_thunk_call_expanded flag.
(ix86_pc_thunk_call_expanded): New define.
* config/i386/i386.md (set_got, set_got_labelled): New expanders.
(*set_got): Rename insn pattern from set_got.
(*set_got_labelled): Rename inst pattern from set_got_labelled.
* config/i386/i386.c (ix86_compute_frame_layout): Use
ix86_pc_thunk_call_expanded to prevent red-zone.
The patch is bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
Uros.
Index: i386.c
===================================================================
--- i386.c (revision 234014)
+++ i386.c (working copy)
@@ -11524,6 +11524,7 @@ ix86_compute_frame_layout (struct ix86_frame *fram
if (ix86_using_red_zone ()
&& crtl->sp_is_unchanging
&& crtl->is_leaf
+ && !ix86_pc_thunk_call_expanded
&& !ix86_current_function_calls_tls_descriptor)
{
frame->red_zone_size = to_allocate;
Index: i386.h
===================================================================
--- i386.h (revision 234014)
+++ i386.h (working copy)
@@ -2494,6 +2494,10 @@ struct GTY(()) machine_function {
expander to determine the style used. */
BOOL_BITFIELD use_fast_prologue_epilogue : 1;
+ /* Nonzero if the current function calls pc thunk and
+ must not use the red zone. */
+ BOOL_BITFIELD pc_thunk_call_expanded : 1;
+
/* If true, the current function needs the default PIC register, not
an alternate register (on x86) and must not use the red zone (on
x86_64), even if it's a leaf function. We don't want the
@@ -2533,6 +2537,7 @@ struct GTY(()) machine_function {
#define ix86_varargs_fpr_size (cfun->machine->varargs_fpr_size)
#define ix86_optimize_mode_switching (cfun->machine->optimize_mode_switching)
#define ix86_current_function_needs_cld (cfun->machine->needs_cld)
+#define ix86_pc_thunk_call_expanded (cfun->machine->pc_thunk_call_expanded)
#define ix86_tls_descriptor_calls_expanded_in_cfun \
(cfun->machine->tls_descriptor_call_expanded_p)
/* Since tls_descriptor_call_expanded is not cleared, even if all TLS
Index: i386.md
===================================================================
--- i386.md (revision 234014)
+++ i386.md (working copy)
@@ -12470,7 +12470,18 @@
""
"ix86_expand_prologue (); DONE;")
-(define_insn "set_got"
+(define_expand "set_got"
+ [(parallel
+ [(set (match_operand:SI 0 "register_operand" "=r")
+ (unspec:SI [(const_int 0)] UNSPEC_SET_GOT))
+ (clobber (reg:CC FLAGS_REG))])]
+ "!TARGET_64BIT"
+{
+ if (flag_pic && !TARGET_VXWORKS_RTP)
+ ix86_pc_thunk_call_expanded = true;
+})
+
+(define_insn "*set_got"
[(set (match_operand:SI 0 "register_operand" "=r")
(unspec:SI [(const_int 0)] UNSPEC_SET_GOT))
(clobber (reg:CC FLAGS_REG))]
@@ -12479,7 +12490,19 @@
[(set_attr "type" "multi")
(set_attr "length" "12")])
-(define_insn "set_got_labelled"
+(define_expand "set_got_labelled"
+ [(parallel
+ [(set (match_operand:SI 0 "register_operand" "=r")
+ (unspec:SI [(label_ref (match_operand 1))]
+ UNSPEC_SET_GOT))
+ (clobber (reg:CC FLAGS_REG))])]
+ "!TARGET_64BIT"
+{
+ if (flag_pic && !TARGET_VXWORKS_RTP)
+ ix86_pc_thunk_call_expanded = true;
+})
+
+(define_insn "*set_got_labelled"
[(set (match_operand:SI 0 "register_operand" "=r")
(unspec:SI [(label_ref (match_operand 1))]
UNSPEC_SET_GOT))
