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
