Re: [edk2-devel] About EDK2 supports Self Modifying Code

["Andrew Fish via groups.io" <afish=apple.com@groups.io>]

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We also support Xcode clang so that means we also support Mach-O executables that get converted to PE/COFF. The is a tool called mtoc (mach-o to coff) in a crufty old open source project that does the conversion. 

The reason you are having issues is due to security hardening as the self modifying code is a security risk. It is kind of hard to imagine a case in UEFI that the self modifying code is worth the security risk?. I know Linux does some patching but those are really hot paths that get used a lot, I don’t see that being a pattern that would be common in firmware. The only case I can think you might want SMC is if you were trying to make an UEFI based stress test of some kind? 

It might be helpful if you could explain why you can’t use a dispatch table or just define a UEFI Protocol and construct it on the fly to meet your configuration? To me saying you need Self Modifying Code is kind of like saying you need to write it in assembler since the C compiler is not smart enough, and most of the times people think that they are wrong.  

Thanks,

Andrew Fish

> On Aug 14, 2023, at 8:06 PM, Chao Li <lichao@loongson.cn> wrote:
> 
> Hi Liming, Bob and Yuwei
> 
> There is a need that some code wants to supports Self-Modification, because some program behavior may not be determined during compilation, and I think this demand may be very popular. 
> 
> The permise of Self-Modification is that the section has executable and writable permissions. Adding a new section and giving it executable and writable permissions is a better way, and the 'pragma seg_code' is recognized in Microsoft VS compiler but GCC doesn't. If use the GCC as the compiler, the '.section name flags' of GNU GAS are acceptable.
> 
> But there is a problem, if converting from elf to efi, the user-defined section with W+X or A+W+X will be droped, Elf64Convert.c will scan the file section permission of elf, if the section is A+X, it will be classified into the .text section, if the section is A+W , then it will be classified into the .data section, if the section is A+W+X or W+X, then it will be droped(Elf64Convert.c, line 272 to 325).
> 
> That is:
> 
> If using the VS compiler, the user-defined with executable and writable sections may be perserved, but GCC elf to efi conversion may not.
> 
> 
> 
> Hope hearback from you and discuss the necessity of SMC(Slef-Modifying-Code) and how to implement it.
> 
> 
> 
> 
> Thanks,
> Chao
> 



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