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Date: Sat, 9 Jun 2018 10:43:28 +0300 From: Yury Norov <ynorov@...iumnetworks.com> To: Palmer Dabbelt <palmer@...ive.com> Cc: catalin.marinas@....com, Arnd Bergmann <arnd@...db.de>, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, linux-arch@...r.kernel.org, linux-api@...r.kernel.org, szabolcs.nagy@....com, heiko.carstens@...ibm.com, philipp.tomsich@...obroma-systems.com, joseph@...esourcery.com, sellcey@...iumnetworks.com, Prasun.Kapoor@...iumnetworks.com, schwab@...e.de, agraf@...e.de, bamv2005@...il.com, geert@...ux-m68k.org, Dave.Martin@....com, kilobyte@...band.pl, manuel.montezelo@...il.com, james.hogan@...tec.com, cmetcalf@...lanox.com, pinskia@...il.com, linyongting@...wei.com, klimov.linux@...il.com, broonie@...nel.org, maxim.kuvyrkov@...aro.org, fweimer@...hat.com, Nathan_Lynch@...tor.com, james.morse@....com, ramana.gcc@...glemail.com, schwidefsky@...ibm.com, davem@...emloft.net, christoph.muellner@...obroma-systems.com Subject: Re: [PATCH 04/24] 32-bit userspace ABI: introduce ARCH_32BIT_OFF_T config option On Fri, Jun 08, 2018 at 03:33:51PM -0700, Palmer Dabbelt wrote: > On Fri, 08 Jun 2018 10:32:07 PDT (-0700), catalin.marinas@....com wrote: > > On Wed, May 16, 2018 at 11:18:49AM +0300, Yury Norov wrote: > > > diff --git a/arch/Kconfig b/arch/Kconfig > > > index 76c0b54443b1..ee079244dc3c 100644 > > > --- a/arch/Kconfig > > > +++ b/arch/Kconfig > > > @@ -264,6 +264,21 @@ config ARCH_THREAD_STACK_ALLOCATOR > > > config ARCH_WANTS_DYNAMIC_TASK_STRUCT > > > bool > > > > > > +config ARCH_32BIT_OFF_T > > > + bool > > > + depends on !64BIT > > > + help > > > + All new 32-bit architectures should have 64-bit off_t type on > > > + userspace side which corresponds to the loff_t kernel type. This > > > + is the requirement for modern ABIs. Some existing architectures > > > + already have 32-bit off_t. This option is enabled for all such > > > + architectures explicitly. Namely: arc, arm, blackfin, cris, frv, > > > + h8300, hexagon, m32r, m68k, metag, microblaze, mips32, mn10300, > > > + nios2, openrisc, parisc32, powerpc32, score, sh, sparc, tile32, > > > + unicore32, x86_32 and xtensa. This is the complete list. Any > > > + new 32-bit architecture should declare 64-bit off_t type on user > > > + side and so should not enable this option. > > > > Do you know if this is the case for riscv and nds32, merged in the > > meantime? If not, I suggest you drop this patch altogether and just > > define force_o_largefile() for arm64/ilp32 as we don't seem to stick to > > "all new 32-bit architectures should have 64-bit off_t". > > We (RISC-V) don't have support for rv32i in glibc yet, so there really isn't > a fixed ABI there yet. From my understanding the rv32i port as it currently > stands has a 32-bit off_t (via __kernel_off_t being defined as long), so > this change would technically be a kernel ABI break. > > Since we don't have rv32i glibc yet I'm not fundamentally opposed to an ABI > break. Is there a concrete advantage to this? One obvious advantage is manipulating large files - if file is greater than 2G, you cannot easily mmap(), lseek() etc with 32-bit offset. Another point is unification of layuots for structures like struct stat between 32- and 64-bit worlds. On glibc side it helps to unify 32-bit and 64-bit versions of syscalls. Refer, for example this commit: 3c7f1f59cd161 (Consolidate lseek/lseek64/llseek implementations). Yury
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