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71c8f9cf26
gcc gets confused when -ftrivial-auto-var-init=pattern is used on sparse
bit fields such as 'struct spi_mem_op', which caused the previous false
positive warning about an uninitialized variable:
drivers/mtd/spi-nor/spansion.c: error: 'op' is used uninitialized [-Werror=uninitialized]
In fact, the variable is fully initialized and gcc does not see it being
used, so the warning is entirely bogus. The problem appears to be
a misoptimization in the initialization of single bit fields when the
rest of the bytes are not initialized.
A previous workaround added another initialization, which ended up
shutting up the warning in spansion.c, though it apparently still happens
in other files as reported by Peter Foley in the gcc bugzilla. The
workaround of adding a fake initialization seems particularly bad
because it would set values that can never be correct but prevent the
compiler from warning about actually missing initializations.
Revert the broken workaround and instead pad the structure to only
have bitfields that add up to full bytes, which should avoid this
behavior in all drivers.
I also filed a new bug against gcc with what I found, so this can
hopefully be addressed in future gcc releases. At the moment, only
gcc-12 and gcc-13 are affected.
Cc: Peter Foley <pefoley2@pefoley.com>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110743
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108402
Link: https://godbolt.org/z/efMMsG1Kx
Fixes:
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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 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.