Date: Thu, 12 Feb 2015 08:30:10 -0800 From: "H.J. Lu" <hjl.tools@...il.com> To: Catalin Marinas <catalin.marinas@....com> Cc: Andy Lutomirski <luto@...capital.net>, Rich Felker <dalias@...c.org>, GNU C Library <libc-alpha@...rceware.org>, Andrew Pinski <pinskia@...il.com>, musl@...ts.openwall.com, LKML <linux-kernel@...r.kernel.org>, Andrew Pinski <apinski@...ium.com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: [PATCHv3 00/24] ILP32 support in ARM64 On Thu, Feb 12, 2015 at 7:50 AM, Catalin Marinas <catalin.marinas@....com> wrote: > On Wed, Feb 11, 2015 at 12:15:56PM -0800, Andy Lutomirski wrote: >> On 02/11/2015 11:57 AM, H.J. Lu wrote: >> >>>>trivially satisfied if you consider x32 and x86_64 separate >> >>>>compilation environments, but it's not related to the core issue: that >> >>>>the definition of timespec violates core (not obscure) requirements of >> >>>>both POSIX and C11. At the time you were probably unaware of the C11 >> >>>>requirement. Note that it's a LOT harder to effect change in the C >> >>>>standard, so even if the Austin Group would be amenable to changing >> >>>>the requirement for timespec to allow something like nseconds_t, >> >>>>getting WG14 to make this change to work around a Linux/glibc mistake >> >>>>does not sound practical. >> >>> >> >>>That is very unfortunate. I consider it is too late for x32 to change. >> >> >> >>Why? It's hardly an incompatible ABI change, as long as the >> >>kernel/libc fills the upper bits (for old programs that read them >> >>based on the old headers) when structs are read from the kernel to the >> >>application, and ignores the upper bits (potentially set or left >> >>uninitialized by the application) when strings are passed from >> >>userspace to the kernel. Newly built apps using the struct definition >> >>with 32-bit tv_nsec would need new libc to ensure that the high bits >> >>aren't interpreted, but this could be handled by symbol versioning. >> >> >> > >> >We have considered this option. But since kernel wouldn't change >> >tv_nsec/tv_usec handling just for x32, it wasn't selected. >> >> Did anyone *ask* the kernel people (e.g. hpa)? > > It seems so: > > https://lkml.org/lkml/2011/8/31/244 > > Couple of more replies from hpa: > > https://lkml.org/lkml/2011/8/31/261 > https://lkml.org/lkml/2012/2/8/408 > > It looks like hpa was going to talk the POSIX committee but I don't know > what the conclusion was and didn't follow the thread (at the time I > wasn't interested in ARM ILP32). Just for the record, tv_nsec/tv_usec can be changed to long as long as kernel always read them as 32 bits and write them as 64 bits for both LP64 and ILP32 in 64-bit imespec amd timeval. In glibc, they can be changed to long without breaking existing binaries. For x86-32, 64-bit __time_t must be 64-bit aligned. Otherwise, there will be no padding in 64-bit timespec nor timeval. -- H.J.
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