gcc7 AMD kernel fails to boot

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

AFAICT a kernel built with gcc 6 boots, but with gcc 7 doesn't?

- cvs updated Feb 11 21:13 UTC code
- built new kernel using config, cd ../compile..., make depend && make (so
  with gcc 6)
- rebooted (EFI) (OK)
- built world using build.sh => world built with and installed gcc 7 (also OK)
- tried out and failed to modlad nvmm.kmod
- guessed it was because nvmm was built with gcc 7, but kernel with gcc 6
- rebuilt kernel using config, cd ../compile...,
  make clean && make depend && make
- new kernel fails to boot freezing after ACPI: FACS
- old kernel boots fine:

[     1.000000] avail memory = 31731 MB
[     1.000000] cpu_rng: RDSEED
[     1.000000] timecounter: Timecounters tick every 10.000 msec
[     1.000000] Kernelized RAIDframe activated
[     1.000000] running cgd selftest aes-xts-256 aes-xts-512 done
[     1.000000] timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
[     1.000003] efi: systbl at pa db7dc018
[     1.000003] System manufacturer System Product Name (System Version)
[     1.000003] mainbus0 (root)
[     1.000003] ACPI: RSDP 0x00000000D3E1E000 000024 (v02 ALASKA)
[     1.000003] ACPI: XSDT 0x00000000D3E1E098 0000AC (v01 ALASKA A M I    01072009 AMI  00010013)
[     1.000003] ACPI: FACP 0x00000000D3E2A820 000114 (v06 ALASKA A M I    01072009 AMI  00010013)
[     1.000003] Firmware Warning (ACPI): Optional FADT field Pm2ControlBlock has valid Length but zero Address: 0x0000000000000000/0x1 (20181213/tbfadt-693)
[     1.000003] ACPI: DSDT 0x00000000D3E1E1E0 00C63B (v02 ALASKA A M I    01072009 INTL 20120913)
[     1.000003] ACPI: FACS 0x00000000DAA95D80 000040

... new kernel stops booting here

[     1.000003] ACPI: APIC 0x00000000D3E2A938 0000DE (v03 ALASKA A M I    01072009 AMI  00010013)
[     1.000003] ACPI: FPDT 0x00000000D3E2AA18 000044 (v01 ALASKA A M I    01072009 AMI  00010013)
[     1.000003] ACPI: FIDT 0x00000000D3E2AA60 00009C (v01 ALASKA A M I    01072009 AMI  00010013)
[     1.000003] ACPI: SSDT 0x00000000D3E3B570 0000BF (v01 AMD    AMD PT   00001000 INTL 20120913)

...

[     1.000003] cpu0: AMD Ryzen 7 1700 Eight-Core Processor          , id 0x800f11


Just in case, diffed ident /netbsd and ident /netbsd.old, and there was
no difference.


Cheers,

Patrick