We are working on some code for ARM Cortex M4 on a STM32 chip.
My understanding is that Cortex-M4 has some 32-bit instructions but these are not 32-bit ARM instructions they are just a few special instructions. I thought the glue was for transitioning between ARM and thumb instructions sets. So why does the linker script need the glue?
.text :
{
. = ALIGN(4);
*(.text) /* .text sections (code) */
*(.text*) /* .text* sections (code) */
*(.glue_7) /* glue arm to thumb code */
*(.glue_7t) /* glue thumb to arm code */
Can I remove the glue_7 and glue_7t since the processor only supports thumb instructions? Would there be any flash memory freed up by doing this?
The posted script is always going to create the sections for ARM/thumb code calling thumb/ARM, if there is nothing to call, the sections are empty. An empty section is benign.
If you want to remove unused sections without modifying the linker, a clean way is performing the dead code elimination, via --gc-sections:
Once the objects and static libraries are created with these options, the linker can perform the dead code elimination. You can do this by setting the -Wl,--gc-sections option to gcc command or in the -largs section of gnatmake. This will perform a garbage collection of code and data never referenced.