Multicall binary fails to dispatch when invoked via fexecve/execveat(..., AT_EMPTY_PATH) — derives util name from binary path instead of argv[0]

[simonvik]

When the coreutils multicall binary is executed via fexecve(3) / execveat(2) with AT_EMPTY_PATH, execution fails with:

coreutils: unknown program '<fd>'

even though argv[0] is set to a valid utility name (e.g. /bin/echo).

It seems like: AT_EXECFN = /dev/fd/<fd>

And the call looks like :
execveat(3, "", ["/bin/echo", "-n", "param1", "param2", "param3"], 0x7ffeb1056278 /* 0 vars */, AT_EMPTY_PATH) = 0

Tested on ubuntu 26.04 with rust-corutils 0.8.0-0ubuntu3

[oech3]

We have support for shebang and /proc/self/fd. Is /dev/fd common?