The Cookie Jar

1. The Cookie Jar pointer

The system maintains a global pointer to the Cookie Jar. The address of the pointer is 0x05a0 ($05a0). This location finds itself in the supervisor area, however, it is strongly discouraged to enter the supervisor mode to read the vector. Using system calls is more appro- priate and will be more compatible with future versions of MiNT.

The Cookie Jar pointer is returned on the following system calls:

a) BIOS' Setexc() function:

jar_address = Setexc(0x0168, -1L);

b) MiNT Ssystem() function:

jar_address = Ssystem(S_GETLVAL, 0x05a0L, 0L);

The first method also works in TOS.

2. Manipulating cookies

The Cookie Jar is guaranteed to be located in memory area, that is accessible for applications in user mode. As a result, once the Cookie Jar pointer has been obtained the way specified above, it is legal to directly manipulate the cookies. However, the operating system provides functions that may facilitate doing that:

• Ssystem(S_GETCOOKIE, tag, &value)

Reads the cookie tag and stores its value in value.

• Ssystem(S_SETCOOKIE, tag, value);

Stores new cookie in the Cookie Jar.

• Ssystem(S_DELCOOKIE, tag, 0L);

Removes the cookie from the Cookie Jar.

Refer to the Ssystem() call documentation for further details.

3. Caveats

• 1) Application programs should NEVER EVER create new Cookie Jar entries, especially if the information stored could get invalid when the application terminates. The Jar is a BIOS resource that provides an information for applications about BIOS services, NOT an area, where applications store data to use for other applications.
• 2) Nobody, not even resident programs, should store pointers as the Jar entry value. Following such pointers is simply illegal for application programs.

draco@atari.org 16.III.2003.