GCC-15 doesn't guarantee that a {0} initializer clears the whole union [1].
This may cause bugs if data is not intialized properly.

The kernel enabld the -fzero-init-padding-bits=all option to tackle the
issue, which was merged in commit dce4aab8441d ("kbuild: Use
-fzero-init-padding-bits=all").

This series propagates the same flag to the tools build.  It uses
tools/scripts/Makefile.include as the central place to add the
option to EXTRA_CFLAGS and HOST_EXTRACFLAGS for the CC and HOSTCC
compilers.  Each project under tools/ appends the variables as needed.

The variable name HOST_EXTRACFLAGS comes from kbuild conventions (see
Documentation/kbuild/makefiles.rst).

This series is divided into three parts:

  Patches 01 – 04: Preparation before adding the new compiler option.
                   These patches adjust Makefiles to ensure the newly
                   introduced option does not cause regressions.
  Patch 05:        Propagate -fzero-init-padding-bits=all to
                   EXTRA_CFLAGS and HOST_EXTRACFLAGS for the
                   CC and HOSTCC compilers, respectively.
  Patches 06 – 30: Apply EXTRA_CFLAGS and HOST_EXTRACFLAGS in
                   project Makefiles.

The change has been verified:

Test 1: cross compiling perf with aarch64 GCC-15.2 [2]:

  ARCH=arm64 CROSS_COMPILE=aarch64-none-linux-gnu- \
       make LDFLAGS="-static" -C tools/perf VF=1 NO_JEVENTS=1 \
       DEBUG=1 V=1 NO_LIBELF=1 NO_LIBTRACEEVENT=1

Test 2: native selftest build on Arm64 machine:

  make -C tools/testing/selftests TARGETS=hid SKIP_TARGETS="" V=1

[1] https://gcc.gnu.org/gcc-15/changes.html
[2] https://developer.arm.com/-/media/Files/downloads/gnu/15.2.rel1/binrel/arm-gnu-toolchain-15.2.rel1-x86_64-aarch64-none-linux-gnu.tar.xz

Signed-off-by: Leo Yan <leo.yan@arm.com>
---
Changes in v3:
- Extended to support cross compilation (Quentin).
- Link to v2: https://lore.kernel.org/r/20260224-tools_build_fix_zero_init-v2-1-b1acc817a01e@arm.com

---
Leo Yan (30):
      bpftool: Avoid adding EXTRA_CFLAGS to HOST_CFLAGS
      libbpf: Initialize CFLAGS before including Makefile.include
      tools: lib: thermal: Initialize CFLAGS before including Makefile.include
      tools/thermal: Initialize CFLAGS before including Makefile.include
      tools build: Append -fzero-init-padding-bits=all to extra cflags
      bpftool: Append extra host flags
      perf build: Append extra host flags
      tools/bpf: build: Append extra cflags
      tools build: Append extra host cflags
      tools build: Append extra cflags for feature
      tools: bootconfig: Append extra cflags
      tools: counter: Append extra cflags
      tools: dma: Append extra cflags
      tools: gpio: Append extra cflags
      tools: hv: Append extra cflags
      tools: iio: Append extra cflags
      tools: mm: Append extra cflags
      tools: nolibc: Append extra cflags
      tools: objtool: Append extra host cflags
      tools: power: acpi: Append extra cflags
      tools: power: x86/intel-speed-select: Append extra cflags
      tools: sched_ext: Append extra cflags
      tools: spi: Append extra cflags
      tools: tracing: Append extra cflags
      tools: usb: Append extra cflags
      tools: verification: Append extra cflags
      selftests/bpf: Append extra cflags
      selftests/hid: Append extra cflags
      selftests/nolibc: Append extra cflags
      selftests/sched_ext: Append extra cflags

 tools/bootconfig/Makefile                      |  1 +
 tools/bpf/Makefile                             |  1 +
 tools/bpf/bpftool/Makefile                     |  9 +++++++--
 tools/build/Makefile                           |  6 ++++--
 tools/build/feature/Makefile                   |  2 ++
 tools/counter/Makefile                         |  1 +
 tools/dma/Makefile                             |  1 +
 tools/gpio/Makefile                            |  1 +
 tools/hv/Makefile                              |  1 +
 tools/iio/Makefile                             |  1 +
 tools/include/nolibc/Makefile                  |  2 +-
 tools/lib/bpf/Makefile                         | 16 ++++++++-------
 tools/lib/thermal/Makefile                     | 16 ++++++++-------
 tools/mm/Makefile                              |  1 +
 tools/objtool/Makefile                         |  2 ++
 tools/perf/Makefile.config                     |  2 +-
 tools/power/acpi/Makefile.config               |  1 +
 tools/power/x86/intel-speed-select/Makefile    |  1 +
 tools/sched_ext/Makefile                       |  1 +
 tools/scripts/Makefile.include                 | 28 ++++++++++++++++++++++++++
 tools/spi/Makefile                             |  1 +
 tools/testing/selftests/bpf/Makefile           |  1 +
 tools/testing/selftests/hid/Makefile           |  1 +
 tools/testing/selftests/nolibc/Makefile.nolibc |  3 +++
 tools/testing/selftests/sched_ext/Makefile     |  1 +
 tools/thermal/lib/Makefile                     | 16 ++++++++-------
 tools/tracing/latency/Makefile                 |  1 +
 tools/usb/Makefile                             |  1 +
 tools/verification/rv/Makefile                 |  1 +
 29 files changed, 93 insertions(+), 27 deletions(-)
---
base-commit: 4ae12d8bd9a830799db335ee661d6cbc6597f838
change-id: 20260224-tools_build_fix_zero_init-dc5261bd8b8b

Best regards,
-- 
Leo Yan <leo.yan@arm.com>