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In __startup_64(), the bool 'la57' can only assume the 'true' value if CONFIG_X86_5LEVEL is enabled in the build, and generally, the compiler can make this inference at build time, and elide any references to the symbol 'level4_kernel_pgt', which may be undefined if 'la57' is false. As it turns out, GCC 12 gets this wrong sometimes, and gives up with a build error: ld: arch/x86/kernel/head64.o: in function `__startup_64': head64.c:(.head.text+0xbd): undefined reference to `level4_kernel_pgt' even though the reference is in unreachable code. Fix this by duplicating the IS_ENABLED(CONFIG_X86_5LEVEL) in the conditional that tests the value of 'la57'. Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20241209094105.762857-2-ardb+git@google.com Closes: https://lore.kernel.org/oe-kbuild-all/202412060403.efD8Kgb7-lkp@intel.com/
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 reStructuredText 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.