ARM Compiler toolchain Using the Linker - ARM Information Center

4.26 How the linker resolves references
4.26.1 See also
Image structure and generation
When the linker has constructed the list of libraries, it repeatedly scans each library in the list to
resolve references. There are two separate lists of files that are maintained. The lists are scanned
in the following order to resolve all dependencies:
1. List of system libraries found in the directories specified by --libpath, ARMCC41LIB, or
ARMLIB. These might also be specified by the -Jdir[,dir,...] compiler option.
2. The list of all other files that have been loaded. These might be specified by the
-Idir[,dir,...] compiler option.
Each list is scanned using the following process:
1. Search all specified directories to select the most compatible library variants.
2. Add the variants to the list of libraries.
3. Scan each of the libraries to load the required members:
a. For each currently unsatisfied non-weak reference, search sequentially through the
list of libraries for a matching definition. The first definition found is marked for
step b.
The sequential nature of the search ensures that the linker chooses the library that
appears earlier in the list if two or more libraries define the same symbol. This
enables you to override function definitions from other libraries, for example, the
ARM C libraries, by adding your libraries to the input file list. However you must
be careful to consistently override all the symbols in a library member or the
behavior is unpredictable.
b. Load the library members marked in stage 3a. As each member is loaded it might
satisfy some unresolved references, possibly including weak ones. Loading a
library member might also create new unresolved weak and non-weak references.
c. Repeat these stages until all non-weak references are either resolved or cannot be
resolved by any library.
4. If any non-weak reference remains unsatisfied at the end of the scanning operation,
generate an error message.
Concepts
• About weak references and definitions on page 4-32
• How the linker performs library searching, selection, and scanning on page 4-35
• Controlling how the linker searches for the ARM standard libraries on page 4-36
• Specifying user libraries when linking on page 4-38.
Reference
Linker Reference:
• --libpath=pathlist on page 2-96.
Compiler Reference:
• -Idir[,dir,...] on page 3-112
• -Jdir[,dir,...] on page 3-123.
Introducing the ARM Compiler toolchain:
• Toolchain environment variables on page 2-14.
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