P1014: gcc 10.2: mtocrf instructions

[renaud]

We have a PPC P1014 based board that runs Linux 5.9 or 5.11 built with gcc 9.3.0. When building with gcc 10.2.0, the system does not start. Using a BDI3000, i trace the exception to the assembly instruction mtocrf i nthe function fdt_next_node: 03037bc: 7c 08 03 a6 mtlr r0 c03037c0: 83 e1 00 2c lwz r31,44(r1) c03037c4: 7d 90 81 20 mtocrf 8,r12 With gcc 9.3.0, the instructions is mtcrf. I read from the https://www.nxp.com/files-static/32bit/doc/ref_manual/EREF_RM.pdf manual mtocrf can be an illegal instruction to some CPUs. Is there a way to prevent the compiler from using this newer instructions? Cheers

[Pavel]

The P1014 core is e500v2.

See the E500 Core Reference Manual:

https://www.nxp.com/docs/en/reference-manual/E500CORERM.pdf

This manual does not have information about problem for using the mtcrtf instruction.

[renaud · Accepted solution]

I found that when not using the flash -mcpu=8540, the mtcrf instructions is used instead and the kernel boots.

[renaud]

I noticed that when I build our boot loader with gcc 10.2.0, the instruction used is mtcrf not mtocrf.

So I wonder it it is a gcc argument that control its use.

[Pavel]

NXP offers SDK 1.9 for the P1010RDB board. Linux kernel of this SDK is 3.12.37. This SDK provides toolchain for application building.

NXP offers also CodeWarrior for Linux application building:

https://www.nxp.com/design/software/development-software/codewarrior-development-tools/codewarrior-n...

See also the following pages about using CodeWarrior for Linux kernel debugging:

https://community.nxp.com/t5/CodeWarrior-for-QorIQ/Linux-Kernel-Debugging/td-p/226107

https://www.nxp.com/docs/en/user-guide/EPPCELINUXUG.pdf

https://www.nxp.com/docs/en/application-note/AN5001.pdf

[renaud]

Upsteam gcc has posted a patch which will did not make it to gcc 11 but will come later.