Date: Thu, 12 Feb 2015 11:13:54 -0500 From: Rich Felker <dalias@...c.org> To: Catalin Marinas <catalin.marinas@....com> Cc: Andy Lutomirski <luto@...capital.net>, "H.J. Lu" <hjl.tools@...il.com>, 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 03:50:24PM +0000, Catalin Marinas 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). At this point POSIX committee is not sufficient. ISO C specifies timespec now, and as Jens Gustedt mentioned (I don't think his reply made it to the whole CC list; see the musl list archive here: http://www.openwall.com/lists/musl/2015/02/11/21 ), it seems unlikely that one could pose a convincing argument for this requirement to be changed in the C language. Rich
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