RE: RTEMS compilation flag

["Leicester, Pete \(DLSLtd, RAL, CEO\) via Tech-talk" <tech-talk@aps.anl.gov>]

Thanks Andrew for the info. It does indeed appear to be the same optimizer bug  but rather than libcom/calc I am seeing it in the synapps calc modules transform record sCalcPostfix.c. I guess the same fix would work but I will probably stick with using -fno_builtin compiler option for the calc module for now. So far its worked for me and seems a little easier than disabling optimization in individual source files.    

Pete

From: Johnson, Andrew N. <anj@anl.gov>
Sent: 09 September 2025 16:22
To: Leicester, Pete (DLSLtd,RAL,CEO) <peter.leicester@diamond.ac.uk>; 'tech-talk@aps.anl.gov' <tech-talk@aps.anl.gov>
Subject: Re: RTEMS compilation flag

 

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Hi Pete,

 

Congratulations! I’m hoping we’ll get more RTEMS users to help test out the latest changes for RTEMS 6.

 

This issue sounds just like a problem that we have traced to an optimizer bug in GCC. There was a workaround added to the postfix.c file in the 7.0.6 release (in commit 54f2d888) which you might be able to apply if you can’t use a newer version of Base, it turns off optimization when compiling that memcpy(); you would also need to add

ARCH_DEP_CFLAGS += -DRTEMS_HAS_ALTIVEC

to your configure/os/CONFIG.Common.RTEMS-beatnik file to enable it (I assume you’re using the beatnik BSP).

 

HTH,

 

- Andrew

 

-- 

Complexity comes for free, Simplicity you have to work for.

 

On 9/9/25, 3:16 AM, "Tech-talk" <tech-talk-bounces@aps.anl.gov> wrote:

 

I have built my first RTEMS 5.3 IOC. The IOC includes a transform record which when first tested crashed seemingly when a memcpy was encountered in the transform record calc field parsing during iocInit. Addition of a ‘-fno_builtin’ to the compiler options seems to have sorted the problem. I was wondering if others had encountered this problem and whether the addition of this particular compiler flag is common with RTEMS IOC’s or have I missed something?

 

I am using RTEMS 5.3, epics 7.0.7, compiler powerpc-rtems5-g++ (GCC) 7.5.0 20191114 (RTEMS 5, RSB 5.3, Newlib 7947581). To verify the issue I stripped the IOC right back to just one transform record which was enough to show the problem.

 

Pete

 

Peter Leicester

Senior Software Systems Engineer

Diamond Light Source Ltd

 

 

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