Subject: Re: [PATCH v2 0/5] LoongArch: Add kernel relocation and KASLR support
To:     Xi Ruoyao <xry111@xry111.site>
References: <20230207142822.52172-1-xry111@xry111.site>
 <70278d23-aa0e-19d9-796f-78c0fd06fee0@loongson.cn>
 <87b9f23ba8b123a765c4139c2112aa365546c1e5.camel@xry111.site>
Cc:     Jinyang He <hejinyang@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>,
        Xuerui Wang <kernel@xen0n.name>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org
From:   Youling Tang <tangyouling@loongson.cn>
Message-ID: <c11aae17-838f-3741-0c13-1c830ac30a56@loongson.cn>
Date:   Thu, 9 Feb 2023 14:34:53 +0800
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On 02/08/2023 04:27 PM, Xi Ruoyao wrote:
> On Wed, 2023-02-08 at 12:37 +0800, Youling Tang wrote:
>> In the case of "[Patch v2 2/5] LoongArch: use la.pcrel instenad of
>> la.abs for exception handlerS", the above failure will occur.
>>
>> Patch2 may have certain problems when using the old toolchains.
>>
>> Youling.
>
> Thanks for the test...
>
> The problem is: old toolchain uses pcaddu12i/ori/lu32i.d/lu52i.d/add.d
> for a 3-operand la.pcrel, while the new toolchain uses
> pcalau12i/addi.d/lu32i/lu52i/add.d.  (I've somehow forgotten all the
> difference!)
>
> We can fix it with something like...
>
>> +void reloc_handler(unsigned long handler, struct handler_reloc *rel)
>> +{
>> +	if (!rel)
>> +		return;
>> +
>> +	for (unsigned long i = 0; i < rel->cnt; i++) {
>> +		unsigned long pc = handler + rel->entries[i].offset;
>> +		unsigned long v = rel->entries[i].sym;
>
>                 /* anchor etc. moved into do_reloc_pcalau12i */
>
>> +		union loongarch_instruction *insn =
>> +			(union loongarch_instruction *)pc;
>
>                 switch insn[0]->reg1i20_format->reg1i20_format {
>                 case pcaddu12i_op:
>                         do_reloc_pcaddu12i(insn, pc, v);
>                         break;
>                 case pcalau12i_op: /* TODO: add it for asm/inst.h */
>                         do_reloc_pcalau12i(insn, pc, v);
>                         break;
>                 default:
>                         panic("what the f**k");
>                 }
>
> Alternatively, we can also emit the pcalau12i/addi.d/lu32i/lu52i
> sequence and overwrite the pcaddu12i/ori sequence generated by the old
> toolchain.
>
> Which way do you like?

v3 tested successfully in both new and old toolchains.

Youling.
>