Re: [PATCH -fixes] riscv: Fix relocatable kernels with early alternatives using -fno-pie

[Alexandre Ghiti <alex@ghiti.fr>]

On 30/05/2023 13:27, Conor Dooley wrote:
> On Mon, May 29, 2023 at 09:37:28PM +0200, Alexandre Ghiti wrote:
>> On 29/05/2023 21:06, Conor Dooley wrote:
>>> On Mon, May 29, 2023 at 08:51:57PM +0200, Alexandre Ghiti wrote:
>>>> On 28/05/2023 15:56, Conor Dooley wrote:
>>>>> On Sun, May 28, 2023 at 03:42:59PM +0200, Alexandre Ghiti wrote:
>>>>>> Hmmm, it still works for me with both clang and gcc-9.
>>>>> gcc-9 is a bit of a relic, do you have more recent compilers lying
>>>>> around? If not, I can try some older compilers at some point.
>>>>>
>>>>>> You don't have to do that now but is there a way I could get your compiled
>>>>>> image? With the sha1 used to build it? Sorry, I don't see what happens, I
>>>>>> need to get my hands dirty in some debug!
>>>>> What do you mean by "sha1"? It falls with v6.4-rc1 which is a stable
>>>>> hash, if that's what you're looking for.
>>>>>
>>>>> Otherwise,
>>>>> https://github.com/ConchuOD/riscv-env/releases/download/v2022.03/vmlinux.bin
>>>>> (ignore the release crap haha, too lazy to find a proper hosting
>>>>> mechanism)
>>>> Ok, I don't get much info without the symbols, can you also provide the
>>>> vmlinux please? But at least your image does not boot, not during the early
>>>> boot though because the mmu is enabled.
>>> Do you see anything print when you try it? Cos I do not. Iff I have time
>>> tomorrow, I'll go poking with gdb. I'm sorry I have not really done any
>>> investigating, I have been really busy this last week or so with
>>> dt-binding stuff but I should be freer again from tomorrow.
>>>
>>> https://github.com/ConchuOD/riscv-env/releases/download/v2022.03/vmlinux
>>
>> Better, the trap happens in kasan_early_init() when it tries to access a
>> global symbol using the GOT but ends up with a NULL pointer, which is weird.
>> So to me, this is not related to kasan, it happens that kasan_early_init()
>> is the first function called after enabling the mmu, I think you may have an
>> issue with the filling of the relocations.
> Yeah, it reproduces without KASAN.
>
>> Sorry to bother you again, but if
>> at some point you can recompile with DEBUG_INFO enabled, that would be
>> perfect! And also provide the vmlinux.relocs file. Sorry for all that, too
>> bad I can't reproduce it.
> New vmlinux & vmlinux.relocs here:
> https://microchiptechnology-my.sharepoint.com/:u:/g/personal/conor_dooley_microchip_com/EZpFNxYYrnNAh5Z3c-rf0pUBBpdPGTLafqdtfcXRUUBkXw?e=7KKMHX
> They're pretty massive unfortunately & hopefully that is not some
> garbage internal-only link.
> .config is a wee bit different, cos different build machine, but the
> problem still manifests on a icicle. I've added it to the tarball just
> in case.


Ok so I had to recreate the Image from the files you gave me and it 
boots fine using qemu: is that expected? Because you only mention the 
icicle above.


[    0.000000] Linux version 6.4.0-rc1 (conor@wendy) (ClangBuiltLinux 
clang version 15.0.7 (/home/conor/stuff/dev/llvm/clang 
8dfdcc7b7bf66834a761bd8de445840ef68e4d1a), ClangBuiltLinux LLD 15.0.7) 
#1 SMP PREEMPT Tue May 30 12:13:12 IST 2023
[    0.000000] random: crng init done
[    0.000000] Machine model: riscv-virtio,qemu
[    0.000000] earlycon: ns16550a0 at MMIO 0x0000000010000000 (options '')
[    0.000000] printk: bootconsole [ns16550a0] enabled
[    0.000000] printk: debug: skip boot console de-registration.
[    0.000000] efi: UEFI not found.
[    0.000000] OF: reserved mem: 0x0000000080000000..0x000000008003ffff 
(256 KiB) map non-reusable mmode_resv0@80000000
[    0.000000] Zone ranges:
[    0.000000]   DMA32    [mem 0x0000000080000000-0x00000000ffffffff]
[    0.000000]   Normal   [mem 0x0000000100000000-0x000000017fffffff]
[    0.000000] Movable zone start for each node
[    0.000000] Early memory node ranges
[    0.000000]   node   0: [mem 0x0000000080000000-0x000000017fffffff]
[    0.000000] Initmem setup node 0 [mem 
0x0000000080000000-0x000000017fffffff]
[    0.000000] SBI specification v1.0 detected
[    0.000000] SBI implementation ID=0x1 Version=0x10002
[    0.000000] SBI TIME extension detected
[    0.000000] SBI IPI extension detected
[    0.000000] SBI RFENCE extension detected
[    0.000000] SBI SRST extension detected
[    0.000000] SBI HSM extension detected
[    0.000000] riscv: base ISA extensions acdfhim
[    0.000000] riscv: ELF capabilities acdfim
[    0.000000] percpu: Embedded 30 pages/cpu s83872 r8192 d30816 u122880
[    0.000000] Kernel command line: earlycon keep_bootcon 
root=/dev/mmcblk1p2 rootdelay=10 reboot=cold
[    0.000000] Dentry cache hash table entries: 524288 (order: 10, 
4194304 bytes, linear)
[    0.000000] Inode-cache hash table entries: 262144 (order: 9, 2097152 
bytes, linear)
[    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 
1034240
[    0.000000] mem auto-init: stack:all(zero), heap alloc:off, heap free:off

...


>>>> I tried with gcc-12 and it still works fine on my end, so frustrating!
>>> Crap! Also, should you not be enjoying a public holiday rather than
>>> debugging?! Or maybe debugging is enjoyable for you...
>>
>> Ahah, this is what I enjoy doing when the kids finally sleep :)
>>
>>
>> Thank you again for your very quick feedback, really appreciated!
> No worries.
>
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