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Ard Biesheuvel 35aafa1d41 x86/boot/64: Fix spurious undefined reference when CONFIG_X86_5LEVEL=n, on GCC-12
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/
History 2024-12-10 11:16:32 +01:00
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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.