RealView® Compilation Tools Compiler and Libraries Guide 5.6. Tailoring static data access

5.6. Tailoring static data access

This section describes using callouts from the C library to access static data. C library functions that use static data can be categorized as follows:

functions that do not use any static data of any kind, for example fprintf()
functions that manage a static state, such as malloc(), rand(), and strtok()
functions that do not manage a static state, but use static data in a way that is specific to the implementation in the ARM compiler, for example isalpha().

When the C library does something that requires implicit static data, it uses a callout to a function you can replace. These functions are shown in Table 5.6. They do not use semihosting.

Table 5.6. C library callouts

Function	Description
`__rt_errno_addr()`	Called to get the address of the variable `errno`. See __rt_errno_addr().
`__rt_fp_status_addr()`	Called by the floating-point support code to get the address of the floating-point status word. See __rt_fp_status_addr().
`locale` functions	The function `__user_libspace()` creates a block of private static data for the library. See Tailoring locale and CTYPE, and Writing reentrant and thread-safe code.

See also Tailoring the runtime memory model for more information about memory use.

The default implementation of __user_libspace creates a 96-byte block in the ZI segment. Even if your application does not have a main() function, the __user_libspace() function does not normally have to be redefined. However, if you are writing an operating system or a process switcher, you must re-implement this function (see Writing reentrant and thread-safe code).

Note

Exactly which functions use static data in their definitions might change in future releases.

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