Perl index() function broken on some MUSL systems

Describe the bug

A bug in perl and/or musl (there is some disagreement where the actual bug is) requires that -D_GNU_SOURCE be used for building perl for use with musl. Otherwise perl's index() string function fails. There are likely other perl functions that fail, since the underlying cause of the problem is that libc's memmem() function is not available to perl.

OpenWrt version

22.03.2, snapshot, but likely all

OpenWrt target/subtarget

mediatek/mt7622

Device

BPI-R64

Image kind

Official downloaded image

Steps to reproduce

#!/usr/bin/perl

my $string1 = "abcabc";
my $string2 = $string1;
my $affected = index($string1, $string2) != 0 ? "AFFECTED - you need to fix perl!" : "NOT affected - your perl is fine!";

printf "index=%d - your system is %s\n", index($string1, $string2), $affected;

Run the above perl program.

Actual behaviour

On affected systrems (notably aarch64/musl) index will be a large negative number, often -549755813888

Expected behaviour

In the sample program the index of a string in an identical string should always be zero.

Additional info

This bug is fixed in any recent version of perl. It can be fixed in OpenWrt by simply adding -D_GNU_SOURCE explicitly to the cflags through perl's Configure script.

Diffconfig

No response

Terms

• I am reporting an issue for OpenWrt, not an unsupported fork.

Start with the Perl package build configuration and Perl's Configure script, then reproduce the issue with the sample program on an affected musl system. Check that the build passes -D_GNU_SOURCE explicitly and verify that the program reports index=0 instead of a large negative value.