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Stephen reported that the build was broken since commit6d2ef226f2("compiler_attributes.h: drop __has_attribute() support for gcc4"), with errors such as: include/linux/compiler_attributes.h:296:5: warning: "__has_attribute" is not defined, evaluates to 0 [-Wundef] 296 | #if __has_attribute(__warning__) | ^~~~~~~~~~~~~~~ make[2]: *** [arch/powerpc/boot/Makefile:225: arch/powerpc/boot/crt0.o] Error 1 But we expect __has_attribute() to always be defined now that we've stopped using GCC 4. Linus debugged it to the point of reading the GCC sources, and noticing that the problem is that __has_attribute() is not defined when preprocessing assembly files, which is what we're doing here. Our assembly files don't include, or need, compiler_attributes.h, but they are getting it unconditionally from the -include in BOOT_CFLAGS, which is then added in its entirety to BOOT_AFLAGS. That -include was added in commit77433830ed("powerpc: boot: include compiler_attributes.h") so that we'd have "fallthrough" and other attributes defined for the C files in arch/powerpc/boot. But it's not needed for assembly files. The minimal fix is to move the addition to BOOT_CFLAGS of -include compiler_attributes.h until after we've copied BOOT_CFLAGS into BOOT_AFLAGS. That avoids including compiler_attributes.h for asm files, but makes no other change to BOOT_CFLAGS or BOOT_AFLAGS. Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> Debugged-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Tested-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.