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Date: Fri, 1 Apr 2022 15:12:22 +0200 From: Peter Zijlstra <peterz@...radead.org> To: "Gustavo A. R. Silva" <gustavoars@...nel.org> Cc: Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH][next] x86/mm/pgtable: Fix Wstringop-overflow warnings On Thu, Mar 31, 2022 at 07:58:34PM -0500, Gustavo A. R. Silva wrote: > Fix the following -Wstringop-overflow warnings when building with GCC-11: > > .arch/x86/mm/pgtable.c: In function ‘pgd_alloc’: > arch/x86/mm/pgtable.c:437:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] > 437 | if (preallocate_pmds(mm, pmds, PREALLOCATED_PMDS) != 0) > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:437:13: note: referencing argument 2 of type ‘pmd_t **’ > arch/x86/mm/pgtable.c:225:12: note: in a call to function ‘preallocate_pmds.constprop’ > 225 | static int preallocate_pmds(struct mm_struct *mm, pmd_t *pmds[], int count) > | ^~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:440:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] > 440 | if (preallocate_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS) != 0) > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:440:13: note: referencing argument 2 of type ‘pmd_t **’ > arch/x86/mm/pgtable.c:225:12: note: in a call to function ‘preallocate_pmds.constprop’ > 225 | static int preallocate_pmds(struct mm_struct *mm, pmd_t *pmds[], int count) > | ^~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:462:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] > 462 | free_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:462:9: note: referencing argument 2 of type ‘pmd_t **’ > arch/x86/mm/pgtable.c:213:13: note: in a call to function ‘free_pmds.constprop’ > 213 | static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count) > | ^~~~~~~~~ > arch/x86/mm/pgtable.c:455:9: warning: ‘pgd_prepopulate_user_pmd’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] > 455 | pgd_prepopulate_user_pmd(mm, pgd, u_pmds); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:455:9: note: referencing argument 3 of type ‘pmd_t **’ > arch/x86/mm/pgtable.c:320:13: note: in a call to function ‘pgd_prepopulate_user_pmd’ > 320 | static void pgd_prepopulate_user_pmd(struct mm_struct *mm, > | ^~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:464:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=] > 464 | free_pmds(mm, pmds, PREALLOCATED_PMDS); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > arch/x86/mm/pgtable.c:464:9: note: referencing argument 2 of type ‘pmd_t **’ > arch/x86/mm/pgtable.c:213:13: note: in a call to function ‘free_pmds.constprop’ > 213 | static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count) > | ^~~~~~~~~ > > by using pointer notation instead of array notation as a workaround for > the above GCC warnings. 'Workaround' implies the warning is on crack... > This helps with the ongoing efforts to globally enable > -Wstringop-overflow. which puts to question this endeavour, why are you wanting to have this if its crap?
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