The ARM926EJ-S Technical Reference Manual states:
> You can only access CP15 registers with MRC and MCR instructions in a
> privileged mode. CDP, LDC, STC, MCRR, and MRRC instructions, and unprivileged
> MRC or MCR instructions to CP15 cause the Undefined instruction exception to
> be taken.
Furthermore, `MCR p15, 0, <Rd>, c7, c10, 5` (later called Data Memory Barrier)
is not specified for the ARM926. Thus, SDL should not use these cache
instructions on ARMv5.
(cherry picked from commit 139a0931a3ee9808f13e7faecdf9fc4590348f9e)
The real problem is that SDL_atomic.c was built in thumb mode instead of ARM mode, which is required to use the mcr instruction on ARM platforms. Added a compiler error to catch this case so we don't generate code that does infinite recursion.
I also added a potentially better way to handle things on Linux ARM platforms, based on comments in the Chromium headers, which we can try out after 2.0.10 ships.
felix
Compiling even a simple SDL2 'hello world' program with gcc -Wstrict-prototypes (GCC 6.2.1) results in warnings like:
/usr/include/SDL2/SDL_gamecontroller.h:143:1: attention : function declaration isn't a prototype [-Wstrict-prototypes]
extern DECLSPEC int SDLCALL SDL_GameControllerNumMappings();
^~~~~~
It seems there is a missing 'void' between the parentheses.
The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().
