ARM Compiler toolchain Using the Linker - ARM Information Center

4.9 Image entry points
4.9.1 See also
Image structure and generation
An entry point in an image is a location where program execution can start. There are two
distinct types of entry point:
Initial entry point
The initial entry point for an image is a single value that is stored in the ELF
header file. For programs loaded into RAM by an operating system or boot loader,
the loader starts the image execution by transferring control to the initial entry
point in the image.
An image can have only one initial entry point. The initial entry point can be, but
is not required to be, one of the entry points set by the ENTRY directive.
Entry points set by the ENTRY directive
You can select one of many possible entry points for an image. An image can have
only one entry point.
You create entry points in objects with the ENTRY directive in an assembler file. In
embedded systems, this directive is typically used to mark code that is entered
through the processor exception vectors, such as RESET, IRQ, and FIQ.
The directive marks the output code section with an ENTRY keyword that instructs
the linker not to remove the section when it performs unused section elimination.
For C and C++ programs, the __main() function in the C library is also an entry
point.
If an embedded image is to be used by a loader, it must have a single initial entry
point specified in the header. Use the --entry command-line option to select the
entry point.
Tasks
• About specifying an initial entry point on page 4-18.
Reference
Linker Reference:
• --entry=location on page 2-58.
Assembler Reference:
• ENTRY on page 6-65.
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