Bug 894160 – dev-libs/isl-0.24-r2 fails to compile (MUSL-CLANG-SYSTEM): configure: error: No ffs implementation found

• Status: CONFIRMED
• Product: Gentoo Linux

[Description Agostino Sarubbo 2023-02-13 11:13:43 UTC]

https://blogs.gentoo.org/ago/2020/07/04/gentoo-tinderbox/

Issue: dev-libs/isl-0.24-r2 fails to compile (MUSL-CLANG-SYSTEM).
Discovered on: amd64 (internal ref: tinderbox_musl)

NOTE:
(MUSL-CLANG-SYSTEM) in the summary means that bug was found on a machine that runs MUSL libc + clang16 but this bug MAY or MAY NOT BE related to musl/clang16.

[Comment 1 Agostino Sarubbo 2023-02-13 11:13:45 UTC]

Created attachment 850670 [details]
build.log

build log and emerge --info

[Comment 2 Agostino Sarubbo 2023-02-13 11:13:46 UTC]

Created attachment 850672 [details]
1_config.log

1_config.log

[Comment 3 James McGeehan IV 2023-06-10 05:09:15 UTC]

Built successfully with `ac_cv_have_decl_ffs=yes emerge -v1 isl`

Was running into same bug with amd64 clang/musl profile. With help from sam, this seems to do the trick.

[Comment 4 Sam James 2023-06-10 07:17:57 UTC]

configure:21492: checking whether ffs is declared
configure:21492: clang -c -O2 -march=x86-64 -pipe -pipe -frecord-gcc-switches -fno-diagnostics-color -fmessage-length=0   conftest.c >&5
conftest.c:38:10: error: use of undeclared identifier 'ffs'
  (void) ffs;
         ^
1 error generated.
configure:21492: $? = 1

I'm wondering if this ever worked, and if it just happens to work on gcc with the builtin check that follows.

It, at least, needs _GNU_SOURCE.