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charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260513_095024_338060_DF64BCE5 X-CRM114-Status: GOOD ( 25.55 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 12, 2026 at 02:56:16PM +0200, Ard Biesheuvel wrote: > On Mon, 11 May 2026, at 16:40, Jann Horn wrote: > > On Mon, May 11, 2026 at 10:59 AM Ard Biesheuvel wrote: > >> I think we should simply do something along the lines of the below, > >> considering that the size of a data object tends to correlate with > >> its minimum alignment. > >> > >> I do find it rather puzzling that the compiler emits empty_zero_page > >> *after* zero_page_pfn - ideally, we'd combine the below with > >> -fdata-sections so that the linker sees all individual objects, but > >> I suspect that would create some problems elsewhere. > >> > >> > >> --- a/include/asm-generic/vmlinux.lds.h > >> +++ b/include/asm-generic/vmlinux.lds.h > >> @@ -452,7 +452,7 @@ > >> #define RO_AFTER_INIT_DATA \ > >> . = ALIGN(8); \ > >> __start_ro_after_init = .; \ > >> - *(.data..ro_after_init) \ > >> + *(SORT_BY_ALIGNMENT(.data..ro_after_init)) \ > > > > Oh, neat, I didn't realize that's possible. That seems like a nicer > > approach... > > Neat but rather ineffective, unfortunately. (I don't see a size > difference with the arm64 defconfig kernel) > > Given that empty_zero_page only ever gets its address taken, we > might just move it into the linker script if that requires tweaking > anyway. We can just place it at the start of .rodata, which is > already page aligned on most architectures (and will become page > aligned unless EMPTY_ZERO_PAGE is #define'd by the arch linker > script to something else) > > > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -472,6 +472,17 @@ > #endif > #endif > > +#ifndef EMPTY_ZERO_PAGE > +#ifndef __HAVE_COLOR_ZERO_PAGE I don't think we want let architectures that don't use colored zero pages redefine it. If it will be really required we can add the ability to redefine EMPTY_ZERO_PAGE later. > +#define EMPTY_ZERO_PAGE \ > + . = ALIGN(PAGE_SIZE); \ > + empty_zero_page = .; \ > + . += PAGE_SIZE; > +#else > +#define EMPTY_ZERO_PAGE > +#endif > +#endif > + > /* > * Read only Data > */ > @@ -479,6 +490,7 @@ > . = ALIGN((align)); \ > .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ > __start_rodata = .; \ > + EMPTY_ZERO_PAGE \ > *(.rodata) *(.rodata.*) *(.data.rel.ro*) \ > SCHED_DATA \ > -- Sincerely yours, Mike.