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### `ld`'s support for interworking between ARM and Thumb code

For the ARM, `ld` will generate code stubs to allow functions calls betweem ARM and Thumb code. These stubs only work with code that has been compiled and assembled with the `-mthumb-interwork` command line option. If it is necessary to link with old ARM object files or libraries, which have not been compiled with the -mthumb-interwork option then the `--support-old-code` command line switch should be given to the linker. This will make it generate larger stub functions which will work with non-interworking aware ARM code. Note, however, the linker does not support generating stubs for function calls to non-interworking aware Thumb code.

The `--thumb-entry` switch is a duplicate of the generic `--entry` switch, in that it sets the program's starting address. But it also sets the bottom bit of the address, so that it can be branched to using a BX instruction, and the program will start executing in Thumb mode straight away.