Hello Wolfgang, you wrote:
R29 was an unlucky choice as with recent toolchains (gcc-4.2.x) gcc will refuse to use load/store multiple insns; instead, it issues a list of simple load/store instructions upon function entry and exit, resulting in bigger code size, which in turn makes the build for a few boards fail.
Use r2 instead.
How about switching r14 (GOT ptr) to r13 in a similar way? Quite like the r2, r13 is a dedicated register (small data area purposes) and it would let us avoid using the -ffixed completely.
This would also resolve a general problem with standalone applications that is lurking in the dark: the global data and GOT pointers are not saved/restored upon exception/interrupt, so for example, upon a decrementer hit U-Boot code starts using the dedicated regs blindly, but they could be scratched by the app's code that was interrupted. This doesn't surface with the U-Boot in-tree example applications, as they are built using system config.mk and contain proper -ffixed tweaks and happen to be in sync, but this a general problem, which should be addressed, as is biting applications built outside of U-Boot tree..
If we used another dedicated register for GOT purposes, which applications code would never use by definition, those issues dissapear. Otherwise we need to provide explicit save/restore in the exception prologue/epilogue.
I can provide patches, but let me know your thoughts first.
kind regards, Rafal