Bug the References to fstub removed by some compiling-time

[Princess-of-Sleeping]

First of all, the psp2 kernel has code like this:

	# Simplified code for overview
	movw       r3, #0x0
	movt       r3, #0x0
	cbz        r3, LAB_810023a6
	blx        SceHdmiForDriver_3126A070

This assembly code can be originally reproduced in C code like

if(&SceHdmiForDriver_3126A070 != NULL){
	SceHdmiForDriver_3126A070(...);
}

&SceHdmiForDriver_3126A070 has movw/movt set to 0 by the SCE compiler. This matches the initial assembly code.

And if the kernel finds the SceHdmiForDriver_3126A070 export, this 0 movw/movt is resolved and replaced with a pointer to the SceHdmiForDriver_3126A070 stub.

However, even if you compile the following C code with vitasdk, these ifs are removed by the compiler.

if(&scePowerIsPowerOnline != NULL){
	scePowerIsPowerOnline();
}

Compile witth

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wl,-q -Wall ${-O0/-O1/-O2/-O3/-Os} -fno-inline -fno-rtti -fno-exceptions -std=gnu++17")

to

	push       {r4, lr}
	blx        scePowerIsPowerOnline
	...

but I don't know how to fix this bug.

[isage]

Can you try

if((volatile void*)&scePowerIsPowerOnline != NULL){
	scePowerIsPowerOnline();
}

?

[Princess-of-Sleeping]

same result with -O2

	push       {r4, lr}
	blx        scePowerIsPowerOnline
	blx        scePowerIsPowerOnline

[Princess-of-Sleeping]

According to @isage arm-vita-eabi-gcc -Os -S main.c generated correct code and did not remove the assembly code corresponding to if branches in C code.

Also, scePowerIsPowerOnline was tested with the weak attribute.

Without __attribute__((weak))__ both gcc and snc remove if check on any optimization level.

gcc -Os

        push    {r3, lr}
        ldr     r3, .L6
        cbz     r3, .L2
        bl      scePowerIsPowerOnline
.L6:
        .word   scePowerIsPowerOnline

gcc -03

        push    {r3, lr}
        movw    r3, #:lower16:scePowerIsPowerOnline
        movt    r3, #:upper16:scePowerIsPowerOnline
        movs    r0, #0
        cbz     r3, .L1
        bl      scePowerIsPowerOnline

[Princess-of-Sleeping]

"""Compiling""" with -O3 will output the following assembly code.

	push       {r4, lr}
	movw       r4,#0x0
	movt       r4,#0x0
	cbz        r4,LAB_810016b2
	nop.w
	cbz        r4,LAB_810016b2
	nop.w

LAB_810016b2:
	mov.w      r0, #0x2000000