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The actual size of the following arrays at run-time depends on CONFIG_X86_PAE. 427 pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS]; 428 pmd_t *pmds[MAX_PREALLOCATED_PMDS]; If CONFIG_X86_PAE is not enabled, their final size will be zero (which is technically not a legal storage size in C, but remains "valid" via the GNU extension). In that case, the compiler complains about trying to access objects of size zero when calling functions where these objects are passed as arguments. Fix this by sanity-checking the size of those arrays just before the function calls. Also, the following warnings are fixed by these changes when building with GCC 11+ and -Wstringop-overflow enabled: arch/x86/mm/pgtable.c:437:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] arch/x86/mm/pgtable.c:440:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] arch/x86/mm/pgtable.c:462:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] arch/x86/mm/pgtable.c:455:9: warning: ‘pgd_prepopulate_user_pmd’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] arch/x86/mm/pgtable.c:464:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] This is one of the last cases in the ongoing effort to globally enable -Wstringop-overflow. The alternative to this is to make the originally suggested change: make the pmds argument from an array pointer to a pointer pointer. That situation is considered "legal" for C in the sense that it does not have a way to reason about the storage. i.e.: -static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[]) +static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t **pmds) With the above change, there's no difference in binary output, and the compiler warning is silenced. However, with this patch, the compiler can actually figure out that it isn't using the code at all, and it gets dropped: text data bss dec hex filename 8218 718 32 8968 2308 arch/x86/mm/pgtable.o.before 7765 694 32 8491 212b arch/x86/mm/pgtable.o.after So this case (fixing a warning and reducing image size) is a clear win. Additionally drops an old work-around for GCC in the same code. Link: https://github.com/KSPP/linux/issues/203 Link: https://github.com/KSPP/linux/issues/181 Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/Yytb67xvrnctxnEe@work |
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| README | ||
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.