Re: Fail to bring hart online on HiFive Unleashed

[Troy Benjegerdes <troy.benjegerdes@sifive.com>]

> On Oct 8, 2019, at 1:33 AM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> 
> Le 8 octobre 2019 08:14:58 GMT+02:00, David Abdurachmanov <david.abdurachmanov@sifive.com> a écrit :
>> On Tue, Oct 8, 2019 at 7:30 AM Aurelien Jarno <aurelien@aurel32.net>
>> wrote:
>>> 
>>> On 2019-10-07 22:19, Atish Patra wrote:
>>>> Thanks for the detailed analysis. Can you please keep me and david
>> in
>>>> cc when you report the issue to U-boot ?
>>> 
>>> Yep. I have progressed a bit on that, and now I am not convinced it's
>> an
>>> U-boot issue, it can be a GCC issue.
>>> 
>>> Here are the conditions to reproduce the bug:
>>> - U-boot runs on hart 1, 2 or 3
>>> - the autoboot process is not interrupted
>>> - extlinux is used to boot the kernel
>>> - arch/riscv/lib/bootm.c is compiled with GCC 9 (works fine with GCC
>> 8)
>>> 
>>> When the problem happens, the missing hart actually ends its
>> execution
>>> in an illegal instruction trap trying to execute the FDT (I only
>> noticed
>>> that recently as the message was hidden by the use of earlycon=sbi):
>>> 
>>> | SiFive FSBL:       2018-03-20
>>> | HiFive-U serial #: 00000246
>>> |
>>> | OpenSBI v0.4-50-g30f09fb (Oct  6 2019 21:58:05)
>>> |    ____                    _____ ____ _____
>>> |   / __ \                  / ____|  _ \_   _|
>>> |  | |  | |_ __   ___ _ __ | (___ | |_) || |
>>> |  | |  | | '_ \ / _ \ '_ \ \___ \|  _ < | |
>>> |  | |__| | |_) |  __/ | | |____) | |_) || |_
>>> |   \____/| .__/ \___|_| |_|_____/|____/_____|
>>> |         | |
>>> |         |_|
>>> |
>>> | Platform Name          : SiFive Freedom U540
>>> | Platform HART Features : RV64ACDFIMSU
>>> | Platform Max HARTs     : 5
>>> | Current Hart           : 2
>>> | Firmware Base          : 0x80000000
>>> | Firmware Size          : 104 KB
>>> | Runtime SBI Version    : 0.2
>>> |
>>> | PMP0: 0x0000000080000000-0x000000008001ffff (A)
>>> | PMP1: 0x0000000000000000-0x0000007fffffffff (A,R,W,X)
>>> |
>>> |
>>> | U-Boot 2019.10-rc4-00037-gdac51e9aaf-dirty (Oct 06 2019 - 21:56:51
>> +0000)
>>> |
>>> | CPU:   rv64imafdc
>>> | Model: SiFive HiFive Unleashed A00
>>> | DRAM:  8 GiB
>>> |
>>> | MMC:   spi@10050000:mmc@0: 0
>>> | In:    serial@10010000
>>> | Out:   serial@10010000
>>> | Err:   serial@10010000
>>> | Net:   eth0: ethernet@10090000
>>> | Hit any key to stop autoboot:  0
>>> | switch to partitions #0, OK
>>> | mmc0 is current device
>>> | Scanning mmc 0:2...
>>> | Found /boot/extlinux/extlinux.conf
>>> | Retrieving file: /boot/extlinux/extlinux.conf
>>> | 510 bytes read in 5 ms (99.6 KiB/s)
>>> | U-Boot menu
>>> | 1:      kernel 5.3.4
>>> | 2:      Debian GNU/Linux kernel 5.3.0-trunk-riscv64
>>> | Enter choice: 1
>>> | 1:      kernel 5.3.4
>>> | Retrieving file: /boot/vmlinux-5.3.4
>>> | 9486076 bytes read in 4813 ms (1.9 MiB/s)
>>> | append: root=/dev/mmcblk0p2 rw console=ttySIF0 rootwait
>>> | Retrieving file: /boot/hifive-unleashed-a00.dtb
>>> | 6088 bytes read in 7 ms (848.6 KiB/s)
>>> | ## Flattened Device Tree blob at 88000000
>>> |    Booting using the fdt blob at 0x88000000
>>> |    Using Device Tree in place at 0000000088000000, end
>> 00000000880047c7
>>> |
>>> | Starting kernel ...
>>> |
>>> | exception code: 2 , Illegal instruction , epc  , ra 88000004
>> 88000000
>>> | ### ERROR ### Please RESET the board ###
>> 
>> I think, that's the same issue I had (or still have) a week ago.
>> Just reminder that kernel 5.3 introduced a 64-byte header (thus no
>> need to wrap kernel) at least for Image target. Thus it's booti that
>> boots the kernel on U-Boot side.
>> Thus the 1st instruction of that header is "j 0x40" (to the beginning
>> of the actual kernel).  And 88000004 would definitely hold an illegal
>> instruction.
>> 
>> 0000000000000000 <.data>:
>> 0:       81a0                    j       0x40
>> 2:       0000                    unimp
>> 4:       0000                    unimp
>> 6:       0100                    nop
>> [..]
> 
> Hmm that's the beginning of the kernel code. The address 88000004
> actually corresponds to the FDT. So the hart ending up in a trap
> actually tries to boot the FDT instead of the kernel.
> 
> I haven't spotted any obvious differences between bootm.o compiled with
> GCC 8 and GCC 9. I wonder if there is somehow a race condition because
> some harts are already executing linux while the last one is still
> executing U-boot.

This is from our GCC maintainer, Jim Wilson:

But we've fixed 3 combine optimization bugs on the gcc-9 branch
recently, and I've got a fourth one that I'm working on now, so there
is a good chance that this is a known and already fixed problem. 




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