Linker Scripts

When an eCos application is linked it must be done under the control of a linker script. This script defines the memory areas, addresses and sized, into which the code and data are to be put, and allocates the various sections generated by the compiler to these.

The linker script actually used is in lib/target.ld in the install directory. This is actually manufactured out of two other files: a base linker script and an .ldi file that was generated by the memory layout tool.

The base linker script is usually supplied either by the architecture HAL or the variant HAL. It consists of a set of linker script fragments, in the form of C preprocessor macros, that define the major output sections to be generated by the link operation. The .ldi file, which is #include'ed by the base linker script, uses these macro definitions to assign the output sections to the required memory areas and link addresses.

The .ldi file is supplied by the platform HAL, and contains knowledge of the memory layout of the target platform. These files generally conform to a standard naming convention, each file being of the form:

pkgconf/mlt_<architecture>_<variant>_<platform>_<startup>.ldi

where <architecture>, <variant> and <platform> are the respective HAL package names and <startup> is the startup type which is usually one of ROM, RAM or ROMRAM.

In addition to the .ldi file, there is also a congruously name .h file. This may be used by the application to access information defined in the .ldi file. Specifically it contains the memory layout defined there, together with any additional section names defined by the user. Examples of the latter are heap areas or PCI bus memory access windows.

The .ldi is manufactured by the Memory Layout Tool (MLT). The MLT saves the memory configuration into a file named

include/pkgconf/mlt_<architecture>_<variant>_<platform>_<startup>.mlt

in the platform HAL. This file is used by the MLT to manufacture both the .ldi and .h files. Users should beware that direct edits the either of these files may be overwritten if the MLT is run and regenerates them from the .mlt file.

The names of the .ldi and .h files are defined by macro definitions in pkgconf/system.h. These are CYGHWR_MEMORY_LAYOUT_LDI and CYGHWR_MEMORY_LAYOUT_H respectively. While there will be little need for the application to refer to the .ldi file directly, it may include the .h file as follows:

#include CYGHWR_MEMORY_LAYOUT_H