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Interpretation when omitted

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This option generates a code for detection of stack smashing at the entry and end of a function.

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A 2-byte area is allocated just before the local variable area (in the direction towards address 0xFFFFF) at the entry to a function, and the value specified by num is stored. After that, the 2-byte area in which num was stored is checked for smashing at the end of the function. If smashing has occurred, the __stack_chk_fail function is called.

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The __stack_chk_fail function needs to be created by the user. It should be defined as a function having no parameters or return values, it should be located in the far area, and the processing to be executed at stack smashing should be written.

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Do not define the function as static.

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When calling another function in the __stack_chk_fail function, note that stack smashing is not detected recursively in the function that was called.

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Specify an integer from 0 to 65535 for num.

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If num is omitted, the compiler automatically determines the integer value.

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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.

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If -stack_protector_all is specified, this option generates a code for detection of stack smashing for all functions.

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If this option is used simultaneously with #pragma stack_protector, the specification by #pragma stack_protector becomes valid.

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A code for detection of stack smashing is not generated for the functions in which the following is specified.

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To generate a code for detection of stack smashing, describe as: