Zoltán Kócsi wrote: > I have a question with regards to ARM interworking. The target is > ARM7TDMI-S, embedded system with no OS. The compiler is arm-elf-gcc, > 4.3.1 with binutils maybe 3 months old. > > It seems that when interworking is enabled then when a piece of THUMB > code calls an other piece of THUMB code in a separate file, it calls > a linker-generated entry point that switches the CPU to ARM mode, then > a jump is executed to an ARM prologue inserted in front of the > target THUMB function that switches the CPU back into THUMB mode. That > is, instead of a simple call, a call, a jump and two mode switches are > executed. > > I also tried the -mcallee-super-interworking flag, which generates a > short ARM to THUMB switching code in front of a THUMB function, but the > final result does not seem to use the .real_entry_ofFUNCTIONNAME entry > point. Rather, it goes through the same switch back and forth routine. > > Is there a way so when both the caller and the callee are compiled with > interworking support the end code switching modes only when it is > necessary? For example, placing a THUMB -> ARM prologue in front of all > functions that are in ARM mode and ARM -> THUMB prologue in front of > THUMB functions and the caller simply calling the real function or the > prologue, depending on its own mode and that of the target? It would > save both code space and execution time.
I don't get it. How would this work? When you have a function pointer you don't know if the target is thumb or ARM code, so how do you know where to jump to? Perhaps you could sketch out an implementation. Andrew.
