Re: [edk2-devel] [RFT PATCH v3 0/5] UefiCpuPkg, OvmfPkg: Simplify CpuExceptionHandlerLib

["Marvin Häuser" <mhaeuser@posteo.de>]

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> On 31. Mar 2023, at 16:39, Ni, Ray <ray.ni@intel.com> wrote:
> 
> 
> 
>> -----Original Message-----
>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Marvin
>> Häuser
>> Sent: Friday, March 31, 2023 7:10 PM
>> To: Ard Biesheuvel <ardb@kernel.org>
>> Cc: Ni, Ray <ray.ni@intel.com>; devel@edk2.groups.io; Andrew Fish
>> <afish@apple.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Liu,
>> Zhiguang <zhiguang.liu@intel.com>; Rebecca Cran <rebecca@bsdio.com>;
>> Tom Lendacky <thomas.lendacky@amd.com>
>> Subject: Re: [edk2-devel] [RFT PATCH v3 0/5] UefiCpuPkg, OvmfPkg: Simplify
>> CpuExceptionHandlerLib
>> 
>> 
>>> On 31. Mar 2023, at 13:03, Ard Biesheuvel <ardb@kernel.org> wrote:
>>> 
>>> On Fri, 31 Mar 2023 at 12:41, Marvin Häuser <mhaeuser@posteo.de> wrote:
>>>> 
>>>> Hi Ray,
>>>> 
>>>>>> On 31. Mar 2023, at 12:09, Ni, Ray <ray.ni@intel.com> wrote:
>>>>> 
>>>>> Ard,
>>>>> What does "-read_only_relocs suppress" control?
>>>> 
>>>> It controls whether relocs that target read-only segments yield a build
>> error or not. I think lld uses “-z notext”.
>>>> 
>>>>> Linker doesn't produce relocation entries that modifies .text section
>> silently
>>>>> so the final .text just cannot run at all?
>>>> 
>>>> Could you please rephrase? I’m not sure I understand, but I think it’s
>> important everyone understands the issues at play to make a good judgment
>> call.
>>>> 
>>> 
>>> As *I* understood it, it means suppress the *warning* not suppress the
>>> *relocation*
> 
> What the meaning of "suppress relocation"?

The option naming is just a bit odd, it suppresses the warning about relocations to read-only segments, not the relocations themselves.

> Why the final binaries are not executable?

I explained that here: https://edk2.groups.io/g/devel/message/102219

TL;dr: Relocations are relative to the first writable segment (thus usually __DATA), so relocations to preceding segments (usually __TEXT) will underflow and thus get corrupted offsets.

Best regards,
Marvin

> 
>> 
>> Correct.
>> 
>>> 
>>> But the resulting binaries are broken, so it doesn't really matter.
>> 
>> 
>> 
>> 
>> 
> 


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