-stack_protector/-stack_protector_all [Professional Edition only] [V2.04.00 or later]

[Format]

-stack_protector[=<numeric value>]

-stack_protector_all[=<numeric value>]

[Description]

-	This option generates a code for detection of stack smashing at the entry and the end of a function. A code for detection of stack smashing consists of instructions executing the three processes shown below.

(1) A 4-byte area is allocated just before (in the direction towards address 0xFFFFFFFF) the local variable area at the entry to a function, and the value specified by <number> is stored in the allocated area.

(2) At the end of the function, whether the 4-byte area in which <number> was stored has been rewritten is checked.

(3) If the 4-byte area has been rewritten in (2), the __stack_chk_fail function is called as the stack has been smashed.

-	A decimal number from 0 to 4294967295 should be specified in <number>. If the specification of <number> is omitted, the compiler automatically select the number.

-	The __stack_chk_fail function needs to be defined by the user. It should contain postprocesses for the detected stack smashing.

-	Note the following items when defining the __stack_chk_fail function.

-	The only possible type of return value is void and any formal parameters not allowed.

-	It is prohibited to call the __stack_chk_fail function as a normal function.

-	The __stack_chk_fail function is not subject to generating a code for detection of stack smashing due to the -stack_protector and -stack_protector_all options and #pragma stack_protector.

-	In a C++ program, add extern "C" to the definition or the declaration for __stack_chk_fail function.

-	Prevent returning to the caller (the function where stack smashing was detected) by taking measures such as calling abort() in __stack_chk_fail function and terminating the program.

-	Do not define the function as static.

If -stack_protector is specified, this option generates a code for detection of stack smashing for only functions having a structure, union, or array that exceeds eight bytes as a local variable. If -stack_protector_all is specified, this option generates a code for detection of stack smashing for all functions.

-	If these options are used simultaneously with #pragma stack_protector, the specification by #pragma stack_protector becomes valid.

-	Even though these options are specified, a code for detection of stack smashing is not generated for a functions for which one of the following #pragma directives is specified.

#pragma inline, #pragma inline_asm, #pragma entry, #pragma no_stack_protector

[Example]

-	<C source file>

#include <stdio.h>

#include <stdlib.h>

void f1()   // Sample program in which the stack is smashed

    volatile char str[10];

    int i;

    for (i = 0; i <= 10; i++){

       str[i] = i; // Stack is smashed when i=10

#ifdef __cplusplus

extern "C" {

#endif

void __stack_chk_fail(void)

    printf("stack is broken!");

    abort();

#ifdef __cplusplus

#endif

-	<Output code>

When compilation is performed with -stack_protector=0 specified

    .glb    _test

    .glb    ___stack_chk_fail

    .glb    _printf

    .glb    _abort

    .SECTION        P,CODE

_test:

    .STACK  _test=20

    MOV.L #00000000H, R14   ; The specified <number> 0 is stored in the stack area.

    PUSH.L R14

    SUB #0CH, R0

    MOV.L #00000000H, R14

    MOV.L #0000000BH, R15

    ADD #02H, R0, R5

L12:    ; parse_bb

    MOV.B R14, [R5+]

    ADD #01H, R14

    SUB #01H, R15

    BNE L12

L13:    ; return

    MOV.L 0CH[R0], R14      ; Data is loaded from the location where <number> was

    CMP #00H, R14           ; stored at the entry to a function and it is compared

                            ; with the specified <number> 0.

    BNE L15                 ; If they do not match, the program branches to L15.

L14:    ; return

    RTSD #10H

L15:    ; return

    BRA ___stack_chk_fail   ; __stack_chk_fail is called.

___stack_chk_fail:

    .STACK  ___stack_chk_fail=8

    SUB #04H, R0

    MOV.L #_L10, R14

    MOV.L R14, [R0]

    BSR _printf

    ADD #04H, R0

    BRA _abort

.SECTION            L,ROMDATA,ALIGN=4

_L10:

    .byte   "stack is broken!"

    .byte   00H

    .END