Re: [PATCH 0/3] elf: load the main program from AT_EXECFD

* Christian Brauner:

> A Linux binfmt_misc handler can dispatch a program to a chosen dynamic
> linker.  This is how you run a program under a different or newer ld.so.

Ahem, you'd use an explicit ld.so invocation for that?

> When the handler is registered with the 'O' (open binary) or 'C'
> (credentials) flag, the kernel keeps the executed file open across the
> dispatch.  It hands the descriptor to the interpreter in the AT_EXECFD
> auxiliary vector entry.  This is the SVR4 contract.  AT_EXECFD is "the
> file descriptor of the program to load", the alternative to AT_PHDR.
> FreeBSD's rtld consumes it, and qemu-user has consumed it since 2013.
>
> The GNU dynamic linker never has.  When such a handler dispatches to
> ld.so, the descriptor is ignored.  It leaks into the new program.  ld.so
> opens the executable again, this time by the path spliced into the
> argument vector.

Adding this functionality to ld.so seems reasonable in principle.

What does /proc/self/exe look like for such processes?  Does GDB work?
There are two cases to consider: launching with GDB, and attaching GDB
to a running process with the -p option.

Thanks,
Florian