warnings while trying to compile old linux kernel with gcc 12.1.0 - gcc

Question

I am currently hunting a bug using git bisect in linux staging-testing tree.
Some commits are giving following errors after I try to build them:
subcmd-util.h:58:31: error: pointer may be used after ‘realloc’ [-Werror=use-after-free]
58 | ret = realloc(ptr, 1);
check.c:2867:58: error: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size 9 [-Werror=format-truncation=]
2867 | snprintf(pvname, sizeof(pvname), "pv_ops[%d]", idx);
I tried adding -Wno-error=use-after-free to KBUILD_FLAGS in main Makefile, tried adding
KBUILD_CFLAGS += $(call cc-disable-warning, use-after-free)
I even tried removing -Werror from CFLAGS in Makefile in folder where problematic files are located, but nothing worked.
More information:
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-bootstrap --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.artixlinux.org/ --with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit --enable-cet=auto --enable-checking=release --enable-clocale=gnu --enable-default-pie --enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-multilib --enable-plugin --enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch --disable-werror --with-build-config=bootstrap-lto --enable-link-serialization=1
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.1.0 (GCC)
Linux staging tree: git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git.
One of the commits that gives following warnings: 2ab9c9675fe892e7fe9fa8c0a6125e2b40d2889d.

Answer 1

To compile older version of kernel I needed older compiler ("Linux kernel sources are in general not forward-compatible with new compilers"). In my case the kernel version was 5.16.0 and I could compile it with gcc 11. If you have gcc 11 specific warnings then try gcc 10 and so on.
Except CC flags, I also needed set to HOSTCC flags to use gcc-11 compiler:
make HOSTCC=gcc-11 CC=gcc-11