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Thu, 1 Jan 2026 18:15:45 -0500 (EST) Date: Fri, 2 Jan 2026 10:15:39 +1100 (AEDT) From: Finn Thain To: Randy Dunlap cc: Sasha Levin , Peter Zijlstra , Ard Biesheuvel , Andrew Morton , Will Deacon , Arnd Bergmann , Stephen Rothwell , x86@kernel.org, Linux Kernel Mailing List , Linux Next Mailing List Subject: Re: linux-next: build failure after merge of the mm-nonmm-unstable tree In-Reply-To: <77d3d65a-9ef0-451e-b24f-1b3f38cf822b@infradead.org> Message-ID: <84ebf3ef-1385-1b11-772b-7bccac4d25ae@linux-m68k.org> References: <20251218153050.44da4a78@canb.auug.org.au> <4a3455a6-a0dc-f7fb-8b68-da471bb312c7@linux-m68k.org> <77d3d65a-9ef0-451e-b24f-1b3f38cf822b@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii On Thu, 1 Jan 2026, Randy Dunlap wrote: > > The following patch produces a build failure. > > > > diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h > > index fd855e32c9b9..8442eebaada1 100644 > > --- a/arch/x86/boot/compressed/misc.h > > +++ b/arch/x86/boot/compressed/misc.h > > @@ -8,6 +8,7 @@ > > * we just keep it from happening. (This list needs to be extended when new > > * paravirt and debugging variants are added.) > > */ > > +#include > > #undef CONFIG_PARAVIRT > > #undef CONFIG_PARAVIRT_XXL > > #undef CONFIG_PARAVIRT_SPINLOCKS > > > > > > Problem is, you can't do #undef unless you know that #define has already > > taken place, and you can't #define again if #undef has already taken > > place... > > > > Anyway, that's just BTW: I don't feel any need to revise the patches I > > sent. > > > > Hi, > You mean something more than > > +#include > +#ifdef CONFIG_PARAVIRT > #undef CONFIG_PARAVIRT > +#endif > +#ifdef CONFIG_PARAVIRT_XXL > #undef CONFIG_PARAVIRT_XXL > +#endif > +#ifdef CONFIG_PARAVIRT_SPINLOCKS > #undef CONFIG_PARAVIRT_SPINLOCKS > +#endif > That's not what I meant. Perhaps I should have said, you can't #undef unless you know that #include has already taken place. That is, if some header does #undef CONFIG_FOO on the assumption that #include has already taken place, then it is fragile. autoconf.h contains no multiple inclusion guard, and it gets included by multiple other headers, so it is prone to 0, 1 or N inclusions. Ordering with respect to #undef CONFIG_FOO is anyone's guess... FYI, the build failure I was referring to looks like this. It's actually caused by solving the fragility problem I just described above... LD arch/x86/boot/compressed/vmlinux x86_64-linux-ld: error: unplaced orphan section `.altinstructions' from `arch/x86/boot/compressed/ident_map_64.o' x86_64-linux-ld: error: unplaced orphan section `.altinstr_replacement' from `arch/x86/boot/compressed/ident_map_64.o' x86_64-linux-ld: error: unplaced orphan section `.altinstr_aux' from `arch/x86/boot/compressed/ident_map_64.o' x86_64-linux-ld: arch/x86/boot/compressed/ident_map_64.o: in function `ident_p4d_init': ident_map_64.c:(.text+0x57f): undefined reference to `__pti_set_user_pgtbl' x86_64-linux-ld: arch/x86/boot/compressed/ident_map_64.o: in function `kernel_ident_mapping_init': ident_map_64.c:(.text+0x8ab): undefined reference to `__pti_set_user_pgtbl' x86_64-linux-ld: arch/x86/boot/compressed/ident_map_64.o:(.altinstr_aux+0x2): undefined reference to `boot_cpu_data' x86_64-linux-ld: arch/x86/boot/compressed/ident_map_64.o:(.altinstr_aux+0x14): undefined reference to `boot_cpu_data' x86_64-linux-ld: arch/x86/boot/compressed/ident_map_64.o:(.altinstr_aux+0x26): undefined reference to `boot_cpu_data' x86_64-linux-ld: arch/x86/boot/compressed/vmlinux: hidden symbol `__pti_set_user_pgtbl' isn't defined x86_64-linux-ld: final link failed: bad value make[3]: *** [arch/x86/boot/compressed/Makefile:119: arch/x86/boot/compressed/vmlinux] Error 1 make[2]: *** [arch/x86/boot/Makefile:96: arch/x86/boot/compressed/vmlinux] Error 2 make[1]: *** [arch/x86/Makefile:310: bzImage] Error 2 make: *** [Makefile:248: __sub-make] Error 2 If you wish to try that experiment, you'll probably need something like this: ./scripts/config -e WERROR -e LD_ORPHAN_WARN --set-str LD_ORPHAN_WARN_LEVEL error -e EFI_STUB -e CPU_SUP_AMD -e AMD_MEM_ENCRYPT