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-Xstack_protector/-Xstack_protector_all [Professional Edition only] |
This option specifies generation of a code for detection of stack smashing.
A code for detection of stack smashing is not generated.
This option generates a code for detection of stack smashing at the entry and end of a function. A code for detection of stack smashing indicates the instructions for executing the three processes shown below. |
(1) A 4-byte area is allocated just before the local variable area (in the direction towards address 0xFFFFFFFF) at the entry to a function, and the value specified by num is stored in the allocated area.
(2) At the end of the function, whether the 4-byte area in which num was stored has been rewritten is checked.
(3) If the value 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 num. If the specification of num is omitted, the compiler automatically specifies the number. |
The __stack_chk_fail function needs to be defined by the user and the processing to be executed upon detection of stack smashing should be written. Note the following items when defining the __stack_chk_fail function. |
The only possible type of return value is void and the __stack_chk_fail function does not have formal parameters. |
The __stack_chk_fail function is not subject to generating a code for detection of stack smashing due to the -Xstack_protector and -Xstack_protector_all options and #pragma stack_protector. |
Prevent returning to the caller, that is, the function where stack smashing was detected by taking measures such as calling abort() in the __stack_chk_fail function to terminate the program. |
When calling another function in the __stack_chk_fail function, note that stack smashing is not detected recursively in the function that was called. |
When this facility is used for a function for which PIC (see "8.6 PIC/PID Facility") is performed, PIC should also be performed for the __stack_chk_fail function. |
If -Xstack_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 -Xstack_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 this option is specified, a code for detection of stack smashing is not generated for the functions for which one of the following #pragma directives is specified. |
#pragma inline, inline keyword, #pragma inline_asm, #pragma no_stack_protector