[PATCH V7 1/4] rust: Fix a race condition in Makefile

[Miguel Ojeda]

On Sun, Mar 29, 2026 at 6:03 PM Mukesh Kumar Chaurasiya (IBM)
<mkchauras at gmail.com> wrote:
>
> When compiling with -j1 flag in powerpc, the libproc_macro finds the
> libcore.rmeta both in toolchain and local rust directory. libproc_macro
> should use the toolchain provided libcore.rmeta.

By toolchain, do you mean the sysroot one or something else?

We should make it such that `rustc` does not try to use them to begin
with, e.g. we added `--sysroot=/dev/null` to prevent that in the past,
please see:

  71479eee9da8 ("rust: Suppress searching builtin sysroot")

In other words, we should try to avoid adding dependencies (even if
order-only) to workaround the issue, but instead we should get rid of
the root issue.

Otherwise, after a build, if we rebuild only one of them, wouldn't it
find again both? i.e. this is not really a "race condition".