KDS: variable optimized out when compile with O2 and LTO option

[vaughn]

Hi all. I have two questions.

In the startup.c file, the stack pointer declaration _SP_INIT as char[], when I add LTO option with linker, there's a warning: "warning: type of '__SP_INIT' does not match original declaration", I want to disable it, and not know how?

And the second one is that, when compiled with O2, I found a locale variable is optimized out which used in asm instructions. So, my question is that, how to avoid this in ALL of source files generated by Processor Export?

[vaughn]

could anybody give some suggestions?

[BlackNight]

I have been running into this for myself in the past too. I'll put together a more detailed response to you (should be able to provide that today).

But I don't see your second problem about that local variable optimized? Can you provide more details about this?

Thanks,

Erich

[vaughn]

Thanks Erich.

The local variable optimized away when I removed the __attribute__(optimze("O0"))

As compare, I remove the comment, and it display as following

[BlackNight]

That's normal and expected with higher optimization settings. If you want to keep it, the usual way is to define the variable with 'volatile'.

[vaughn]

hi Erich, I found local variable will optimized away even if volatile added, and GCC's version is arm-none-eabi-gcc 4.9.3.

an usage as follow:

#define CpuCriticalVar()    uint8_t cpuSR

#define CpuEnterCritical()    \
  do {                        \
    __asm volatile (                    \
    "MRS   R0, PRIMASK\n\t"    \
    "CPSID I\n\t"            \
    "STRB R0, %[output]"    \
    : [output] "=m" (cpuSR) :: "r0");    \
  } while(0)

#define CpuExitCritical()    \
  do{                        \
    __asm volatile (                    \
    "ldrb r0, %[input]\n\t"    \
    "msr PRIMASK,r0;\n\t"    \
    ::[input] "m" (cpuSR) : "r0");    \
  } while(0)

[BlackNight]

you would have to mark the cpuSR as volatile.

[vaughn]

Erich, no effect even if volatile added, so you can try it with compile option -O2 and linked with LTO

[BlackNight]

I have documented how I have been fixing that warning message caused by -flto in GNU Link Time Optimization finds non-matching Declarations | MCU on Eclipse 

I hope this is useful,

Erich

[vaughn]

Erich, that doc helpful, thanks.

And the second question is that, are there bugs similar with optimized away within other modules generated by PE, e.g. UART, MSCAN, SPI. For I found another problem using UART, which runing ok with O0 compile option, and run to UnhandledInterrupt when UART transmit.

[vaughn]

when compiled with O2 and LTO, when run to UART_PDD_EnableInterrupt and continue, it run to UnhandledInterrupt, but i can not location the problem accuratly.

the UART source files attached.

[BlackNight]

To know which interrupt is causing this, turn on 'one for every', see Oh my! An Interrupt… | MCU on Eclipse 

I hope this helps,

Erich

[vaughn]

Thanks Erich, that's great.