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Enable GCC 16's coming "-fdiagnostics-show-context=N" option[1] to provide enhanced diagnostic information for value-tracking warnings, which displays the control flow chain leading to the diagnostic. This covers our existing use of -Wrestrict and -Wstringop-overread, and gets us closer to enabling -Warray-bounds, -Wstringop-overflow, and -Wstringop-truncation, so we can track the rationale for the warning, letting us more quickly identify actual issues vs what have looked in the past like false positives. Fixes based on this work have already been landing, e.g.:4a6f18f286("net/mlx4_core: Avoid impossible mlx4_db_alloc() order value")8a39f1c870("ovl: Check for NULL d_inode() in ovl_dentry_upper()")e5f7e4e0a4("drm/amdgpu/atom: Work around vbios NULL offset false positive") The context depth ("=N") provides the immediate decision path that led to the problematic code location, showing conditional checks and branch decisions that caused the warning. This will help us understand why GCC's value-tracking analysis triggered the warning and makes it easier to determine whether warnings are legitimate issues or false positives. For example, an array bounds warning will now show the conditional statements (like "if (i >= 4)") that established the out-of-bounds access range, directly connecting the control flow to the warning location. This is particularly valuable when GCC's interprocedural analysis can generate warnings that are difficult to understand without seeing the inferred control flow. While my testing has shown that "=1" reports enough for finding the origin of most bounds issues, I have used "=2" here just to be conservative. Build time measurements with this option off, =1, and =2 are all with noise of each other, so there seems to be no harm in "turning it up". If we need to, we can make this value configurable in the future. Link: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=6faa3cfe60ff9769d1bebfffdd2c7325217d7389 [1] Reviewed-by: Miguel Ojeda <ojeda@kernel.org> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Link: https://patch.msgid.link/20251121184342.it.626-kees@kernel.org Signed-off-by: Kees Cook <kees@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.