Kinetis Design Studio中的主题 Re: KDS: variable optimized out when compile with O2 and LTO option

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

vaughn — Tue, 29 May 2018 17:31:59 GMT

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?

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

vaughn — Thu, 31 May 2018 01:44:19 GMT

could anybody give some suggestions?

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

BlackNight — Thu, 31 May 2018 03:36:46 GMT

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

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

vaughn — Thu, 31 May 2018 06:23:48 GMT

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

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

BlackNight — Thu, 31 May 2018 09:00:16 GMT

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'.

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

BlackNight — Thu, 31 May 2018 10:17:55 GMT

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

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

vaughn — Thu, 31 May 2018 13:26:16 GMT

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.

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

vaughn — Thu, 31 May 2018 13:38:23 GMT

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.

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

BlackNight — Thu, 31 May 2018 13:59:01 GMT

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

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

vaughn — Thu, 31 May 2018 18:41:46 GMT

Thanks Erich, that's great.

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

vaughn — Sat, 02 Jun 2018 08:18:48 GMT

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)

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

BlackNight — Mon, 04 Jun 2018 15:17:15 GMT

you would have to mark the cpuSR as volatile.

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

vaughn — Thu, 07 Jun 2018 03:56:09 GMT

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