Overriding __WEAK symbols; ARMGCC Toolchain

[astewart]

In the nRF SDK version 11 (specifically, this download) some functions are either declared or defined to be __WEAK.

I will use app_error_fault_handler(uint32_t, uint32_t, uint32_t) declared in app_error_weak.h and defined in app_error_weak.c as an example.

app_error_fault_handler is both declared and defined as __WEAK. According to the inline documentation, this is supposed to make it possible to override the weak symbol if I would like to in my main.c file.

I'm using the ARM GCC toolchain:

arm-none-eabi-gcc (GNU Tools for ARM Embedded Processors) 5.2.1 20151202 (release) [ARM/embedded-5-branch revision 231848]

The problem, it seems, is that declaring it __WEAK in the header file, which ultimately is included in main.c, makes the declaration in main.c weak as well, and then it is the version in app_error_weak.c that actually ends up in the finished binary.

Is this the intended behavior, or am I missing something here? It seems to me that the header file shouldn't be declaring it __WEAK.

---

I noticed also that in app_error_weak.h is the following:

#ifdef __CC_ARM
	     void app_error_fault_handler(uint32_t id, uint32_t pc, uint32_t info);
#else
	     __WEAK void app_error_fault_handler(uint32_t id, uint32_t pc, uint32_t info);
#endif

So, if __CC_ARM had been defined, it would not have been declared __WEAK. Should __CC_ARM be defined in my build? I'm using the Makefile that came with the ble_app_uart example.

[awneil]

It would seem to make more sense to have the __weak on the definition only - not the declaration.

But it shouldn't matter, as the resolution of the names is all handled by the Linker; which knows nothing of the declarations - only the definitions.

[astewart]

Right, but because the declaration in app_error_weak.h is (indirectly) included in main.c, the symbol for app_error_fault_handler in main.o also gets a weak flag (as shown by arm-none-eabi-objdump). That is ultimately the problem... that it results in weak symbols in both object files.

I suppose I could create a third compilation unit that doesn't ultimately include app_error_weak.h, just to avoid a weak definition, but that seems less desirable to me than just not declaring it as weak in the header

[awneil]

You could ask on the ARM GCC forum what is the intended operation & recommended usage:

answers.launchpad.net/gcc-arm-embedded

[awneil]

Looks like the same issue: devzone.nordicsemi.com/.../

[puz_md]

I agree with astewart, like I already commented in my thread. Header files are copied into implementation fiels by the preprocessor. This is a C specific feature, not GCC specific.