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Nathan Chancellor
4cdcdbe504
When building certain configurations with CONFIG_FINEIBT=y after commit894af4a1cd("objtool: Validate kCFI calls"), there is a warning due to an indirect call in dw_i2c_plat_remove(): $ cat allno.config CONFIG_ACPI=y CONFIG_CFI=y CONFIG_COMMON_CLK=y CONFIG_CPU_MITIGATIONS=y CONFIG_I2C=y CONFIG_I2C_DESIGNWARE_BAYTRAIL=y CONFIG_I2C_DESIGNWARE_CORE=y CONFIG_I2C_DESIGNWARE_PLATFORM=y CONFIG_IOSF_MBI=y CONFIG_MITIGATION_RETPOLINE=y CONFIG_MODULES=y CONFIG_PCI=y CONFIG_X86_KERNEL_IBT=y $ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean allnoconfig vmlinux vmlinux.o: warning: objtool: dw_i2c_plat_remove+0x3c: no-cfi indirect call! With this configuration, i2c_dw_semaphore_cb_table has the BAYTRAIL member and the sentinel (i.e., 2 members), both of which have an implicit .remove = NULL, so Clang effectively turns i2c_dw_remove_lock_support(), which is later inlined into dw_i2c_plat_remove(), into: static void i2c_dw_remove_lock_support(struct dw_i2c_dev *dev) { if (dev->semaphore_idx > 2) (*NULL)(dev): } which is not necessarily problematic from a logic perspective (as the code was not bounds checking semaphore_idx so an out of bounds index could already crash) but objtool's new __nocfi indirect call checking trips over Clang dropping the kCFI setup from a known NULL indirect call. While it would be possible to fix this by transforming the initial check into if (dev->semaphore_idx < 0 || dev->semaphore_idx >= ARRAY_SIZE(i2c_dw_semaphore_cb_table)) the remove member is unused after commit440da737cf("i2c: designware: Use PCI PSP driver for communication"), so i2c_dw_remove_lock_support() can be removed altogether, as it will never actually do anything. Closes: https://github.com/ClangBuiltLinux/linux/issues/2133 Signed-off-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Kees Cook <kees@kernel.org> Reviewed-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org> Signed-off-by: Andi Shyti <andi.shyti@kernel.org> Link: https://lore.kernel.org/r/20251013-dw_i2c_plat_remove-avoid-objtool-no-cfi-warning-v1-1-8cc4842967bf@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.