Re: [PATCH] rust: kbuild: use `pound` to support GNU Make < 4.3

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Apr 14, 2025 at 07:12:41PM +0200, Miguel Ojeda wrote:
> GNU Make 4.3 changed the behavior of `#` inside commands in commit
> c6966b323811 ("[SV 20513] Un-escaped # are not comments in function
> invocations"):
> 
>     * WARNING: Backward-incompatibility!
>       Number signs (#) appearing inside a macro reference or function invocation
>       no longer introduce comments and should not be escaped with backslashes:
>       thus a call such as:
>         foo := $(shell echo '#')
>       is legal.  Previously the number sign needed to be escaped, for example:
>         foo := $(shell echo '\#')
>       Now this latter will resolve to "\#".  If you want to write makefiles
>       portable to both versions, assign the number sign to a variable:
>         H := \#
>         foo := $(shell echo '$H')
>       This was claimed to be fixed in 3.81, but wasn't, for some reason.
>       To detect this change search for 'nocomment' in the .FEATURES variable.
> 
> Unlike other commits in the kernel about this issue, such as commit
> 633174a7046e ("lib/raid6/test/Makefile: Use $(pound) instead of \#
> for Make 4.3"), that fixed the issue for newer GNU Makes, in our case
> it was the opposite, i.e. we need to fix it for the older ones: someone
> building with e.g. 4.2.1 gets the following error:
> 
>     scripts/Makefile.compiler:81: *** unterminated call to function 'call': missing ')'.  Stop.
> 
> Thus use the existing variable to fix it.
> 
> Reported-by: moyi geek
> Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/291565/topic/x/near/512001985
> Cc: stable@vger.kernel.org
> Fixes: e72a076c620f ("kbuild: fix issues with rustc-option")
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>