Re: [RFC PATCH 0/2] Introduce a way to expose the interpreted file with binfmt_misc

[Guilherme G. Piccoli]

On 07/09/2023 22:24, Guilherme G. Piccoli wrote:
> Currently the kernel provides a symlink to the executable binary, in the
> form of procfs file exe_file (/proc/self/exe_file for example). But what
> happens in interpreted scenarios (like binfmt_misc) is that such link
> always points to the *interpreter*. For cases of Linux binary emulators,
> like FEX [0] for example, it's then necessary to somehow mask that and
> emulate the true binary path.
> 
> We hereby propose a way to expose such interpreted binary as exe_file if
> the flag 'I' is selected on binfmt_misc. When that flag is set, the file
> /proc/self/exe_file points to the *interpreted* file, be it ELF or not.
> In order to allow users to distinguish if such flag is used or not without
> checking the binfmt_misc filesystem, we propose also the /proc/self/interpreter
> file, which always points to the *interpreter* in scenarios where
> interpretation is set, like binfmt_misc. This file is empty / points to
> nothing in the case of regular ELF execution, though we could consider
> implementing a way to point to the LD preloader if that makes sense...
> 
> This was sent as RFC because of course it's a very core change, affecting
> multiple areas and there are design choices (and questions) in each patch
> so we could discuss and check the best way to implement the solution as
> well as the corner cases handling. This is a very useful feature for
> emulators and such, like FEX and Wine, which usually need to circumvent
> this kernel limitation in order to expose the true emulated file name
> (more examples at [1][2][3]).
> 
> This patchset is based on the currently v6.6-rc1 candidate (Linus tree
> from yesterday) and was tested under QEMU as well as using FEX.
> Thanks in advance for comments, any feedback is greatly appreciated!
> Cheers,
> 
> Guilherme
> 
> 
> [0] https://github.com/FEX-Emu/FEX
> 
> [1] Using an environment variable trick to override exe_file:
> https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/util/u_process.c#L209 
> 
> [2] https://github.com/baldurk/renderdoc/pull/2694
> 
> [3] FEX handling of the exe_file parsing:
> https://github.com/FEX-Emu/FEX/blob/main/Source/Tools/FEXLoader/LinuxSyscalls/FileManagement.cpp#L499
> 
> 

Hi folks, gentle monthly ping.
Any opinions / suggestions on that?

Thanks in advance,


Guilherme