[Bug target/36480] New: stack-protector causes bad ARM PIC code generated

["dougkwan at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

The ARM back-end avoids marking a function as needing PIC in
require_pic_register().  The code there checks if the current IR-type is
IR_GIMPLE or not.  The logic does not work when both -fPIC and
-fstack-protector are given.  The stack protector prologue is generated very
early in RTL expansion when the IR-type is still IR_GIMPLE.  Hence, the current
code ends up using a PIC regiser never gets initialized properly.  

---
extern int sprintf (char *, const char*, ...);

void
test (void)
{
 char buf[10];
 sprintf(buf, "aaaa");
}
---

compiled using top-of-trunk on 6/9/2008

../install/bin/arm-elf-gcc -O2 -S -fdump-rtl-expand -fpic -fstack-protector 
bug.c

Note that vreg 133 is used in insn 4 but never assigned a value.

;;
;; Full RTL generated for this function:
;;
(note 1 0 7 NOTE_INSN_DELETED)

(note 7 1 10 2 [bb 2] NOTE_INSN_BASIC_BLOCK)

(insn 10 7 11 2 bug.c:7 (set (reg:SI 139)
        (unspec:SI [
                (const:SI (minus:SI (const (symbol_ref:SI
("_GLOBAL_OFFSET_TABLE_")))
                        (const:SI (plus:SI (unspec:SI [
                                        (const_int 0 [0x0])
                                    ] 21)
                                (const_int 8 [0x8])))))
            ] 3)) -1 (nil))

(insn 11 10 12 2 bug.c:7 (set (reg:SI 139)
        (unspec:SI [
                (plus:SI (reg:SI 139)
                    (const (plus:SI (pc)
                            (const_int 8 [0x8]))))
                (const_int 0 [0x0])
            ] 4)) -1 (nil))

(insn 12 11 2 2 bug.c:7 (use (reg:SI 139)) -1 (nil))

(note 2 12 3 2 NOTE_INSN_FUNCTION_BEG)

(insn 3 2 4 2 bug.c:5 (set (reg:SI 135)
        (unspec:SI [
                (symbol_ref:SI ("__stack_chk_guard") [flags 0x40] <var_decl
0xf7ec6f78 __stack_chk_guard>)
            ] 3)) -1 (nil))

(insn 4 3 5 2 bug.c:5 (set (reg/f:SI 134)
        (mem/u/c:SI (plus:SI (reg:SI 133)
                (reg:SI 135)) [0 S4 A32])) -1 (expr_list:REG_EQUAL
(symbol_ref:SI ("__stack_chk_guard") [flags 0x40] <var_decl 0xf7ec6f78
__stack_chk_guard>)
        (nil)))


-- 
           Summary: stack-protector causes bad ARM PIC code generated
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dougkwan at google dot com
 GCC build triplet: i686-unknown-linux-gnu
  GCC host triplet: i686-unknown-linux-gnu
GCC target triplet: arm-unknown-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36480