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Clang warns (or errors with CONFIG_WERROR=y):
drivers/gpu/drm/sysfb/efidrm.c:353:11: error: variable 'screen_base' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
353 | else if (mem_flags & EFI_MEMORY_WB)
| ^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/sysfb/efidrm.c:356:7: note: uninitialized use occurs here
356 | if (!screen_base)
| ^~~~~~~~~~~
drivers/gpu/drm/sysfb/efidrm.c:353:7: note: remove the 'if' if its condition is always true
353 | else if (mem_flags & EFI_MEMORY_WB)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
354 | screen_base = devm_memremap(&pdev->dev, mem->start, resource_size(mem),
drivers/gpu/drm/sysfb/efidrm.c:261:27: note: initialize the variable 'screen_base' to silence this warning
261 | void __iomem *screen_base;
| ^
| = NULL
efidrm_get_mem_flags() can only return a mask that has at least one of
the tested values set so the else case is impossible but clang's static
analysis runs before inlining so it cannot know that.
Initialize screen_base to NULL and add a defensive error message in case
mem_flags were ever returned without one of the four valid values.
Fixes: 32ae90c66f ("drm/sysfb: Add efidrm for EFI displays")
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250410-efidrm-avoid-uninit-screen_info-warning-v2-1-b79646f58c24@kernel.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 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.