Building utils with -flto fails ("gpiochips" section is removed)

[Andrii Batyiev]

I'm trying to build utils package on Gentoo, and I have following error:

/usr/bin/aarch64-unknown-linux-gnu-gcc` -O2 -pipe -march=native -flto -Wl,-O1 -Wl,--as-needed pinctrl/CMakeFiles/pinctrl.dir/pinctrl.c.o pinctrl/CMakeFiles/pinctrl.dir/gpiolib.c.o pinctrl/CMakeFiles/pinctrl.dir/util.c.o pinctrl/CMakeFiles/pinctrl.dir/gpiochip_bcm2835.c.o pinctrl/CMakeFiles/pinctrl.dir/gpiochip_bcm2712.c.o pinctrl/CMakeFiles/pinctrl.dir/gpiochip_rp1.c.o -o pinctrl/pinctrl   && :
/usr/lib/gcc/aarch64-unknown-linux-gnu/13/../../../../aarch64-unknown-linux-gnu/bin/ld: /var/tmp/portage/dev-embedded/raspberrypi-utils-0_p20240203/temp/cc7W9zU1.ltrans0.ltrans.o: in function `gpio_find_chip':
<artificial>:(.text+0x630): undefined reference to `__start_gpiochips'
/usr/lib/gcc/aarch64-unknown-linux-gnu/13/../../../../aarch64-unknown-linux-gnu/bin/ld: <artificial>:(.text+0x634): undefined reference to `__start_gpiochips'
/usr/lib/gcc/aarch64-unknown-linux-gnu/13/../../../../aarch64-unknown-linux-gnu/bin/ld: <artificial>:(.text+0x63c): undefined reference to `__stop_gpiochips'
/usr/lib/gcc/aarch64-unknown-linux-gnu/13/../../../../aarch64-unknown-linux-gnu/bin/ld: <artificial>:(.text+0x640): undefined reference to `__stop_gpiochips'
collect2: error: ld returned 1 exit status

It seems like LTO forces to remove "gpiochips" section from files.
Following patch fixes the issue: lto-fix.patch by adding __attribute__((used)) to force gcc to keep necessary sections.

Gentoo bug: https://bugs.gentoo.org/926264

[Phil Elwell]

Thanks - fixed as suggested by 17fdfeb.