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The entry point of a program is at __main in
the C library where library code:
Copies non-root (RO and RW) execution regions from their load addresses to their execution addresses. Also, if any data sections are compressed, they are decompressed from the load address to the execution address.
Zeroes ZI regions.
Branches to __rt_entry.
If you do not want the library to perform these actions, you
can define your own __main that branches
to __rt_entry. For example:
IMPORT __rt_entry EXPORT __main ENTRY __main B __rt_entry END
The library function __rt_entry() runs
the program as follows:
Sets up the
stack and the heap by one of a number of means that include calling __user_setup_stackheap(),
calling __rt_stackheap_init(), or loading the
absolute addresses of scatter-loaded regions.
Calls __rt_lib_init() to initialize
referenced library functions, initialize the locale and, if necessary,
set up argc and argv for main().
For C++, calls the constructors for any top-level objects
by way of __cpp_initialize__aeabi_.
Calls main(), the user-level
root of the application.
From main(), your program might call,
among other things, library functions.
Calls exit() with the value
returned by main().
ARM C and C++ Libraries and Support Reference: