[PATCH 0/1] DTC v1.7.1 Build Error

[Markus Mayer <mmayer@broadcom.com>]

Hi all,

Our automated build environment flagged a new build error introduced by
DTC 1.7.1. Specifically, a compiler option (warning) that was added is
only supported by gcc but not by clang. This results in the build
failing immediately if clang is being used.

clang-18 -I libfdt -I . -DFDT_ASSUME_MASK=0 -DNO_VALGRIND -g -Os -fPIC
  -Werror -Wall -Wpointer-arith -Wcast-qual -Wnested-externs -Wsign-compare
  -Wstrict-prototypes -Wmissing-prototypes -Wredundant-decls -Wshadow
  -Wsuggest-attribute=format -Wwrite-strings  -DNO_YAML -o srcpos.o -c
  srcpos.c
error: unknown warning option '-Wsuggest-attribute=format'; did you mean
  '-Wproperty-attribute-mismatch'? [-Werror,-Wunknown-warning-option]
make: *** [Makefile:359: srcpos.o] Error 1

The commit in question is [1]

e3cde0613bfd Add -Wsuggest-attribute=format warning, correct warnings thus generated

This commit was not part of v1.7.0 and is part of v1.7.1. The problem
is, clang doesn't like this option, and with -Werror enabled, the build
fails. Meanwhile, clang is perfectly capable of building dtc once the
offending option has been removed.

I am submitting a potential solution to this problem that relies on some
Makefile code taken from the Linux kernel to detect if the compiler
supports a certain option or not. Admittedly, the added code is a bit
wordy, but it should work very well going forward if another such
situation occurs. It is also very concise and easy to read when it is
being used.

Lastly, here is some debug output to show how the value of $(WARNINGS)
is affected by the compiler.

# using gcc
$ make
Makefile:49: *** The warnings are: -Wall -Wpointer-arith -Wcast-qual
  -Wnested-externs -Wsign-compare -Wstrict-prototypes -Wmissing-prototypes
  -Wredundant-decls -Wshadow -Wwrite-strings -Wsuggest-attribute=format.
Stop.

# using clang
$ CC=clang-18 make
Makefile:49: *** The warnings are: -Wall -Wpointer-arith -Wcast-qual
  -Wnested-externs -Wsign-compare -Wstrict-prototypes -Wmissing-prototypes
  -Wredundant-decls -Wshadow -Wwrite-strings .
Stop.

As intended, "-Wsuggest-attribute=format" disappears if clang is being
used, and with this, clang can successfully complete the build.

Please let me know what you think.

Thanks,
-Markus

[1] https://git.kernel.org/pub/scm/utils/dtc/dtc.git/commit/?id=e3cde0613bfd

Markus Mayer (1):
  Makefile: only use compiler flags when supported

 Makefile | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

-- 
2.46.0