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Message-ID: <BD7773622145634B952E5B54ACA8E349AA2443B2@PUMAIL01.pu.imgtec.org> Date: Fri, 26 Feb 2016 03:58:47 +0000 From: Jaydeep Patil <Jaydeep.Patil@...tec.com> To: "dalias@...c.org" <dalias@...c.org>, "musl@...ts.openwall.com" <musl@...ts.openwall.com> CC: Mahesh Bodapati <Mahesh.Bodapati@...tec.com> Subject: RE: mips n64 porting review Hi Rich, Thanks for the comments. I will submit the N64 patch with nlink_t changed. Regards, Jaydeep > -----Original Message----- > From: Rich Felker [mailto:dalias@...ifal.cx] On Behalf Of dalias@...c.org > Sent: 25 February 2016 PM 11:53 > To: musl@...ts.openwall.com > Cc: Jaydeep Patil; Mahesh Bodapati > Subject: Re: [musl] mips n64 porting review > > Sorry for dropping the CC. More follow-up below: > > On Thu, Feb 25, 2016 at 01:01:50PM -0500, dalias@...c.org wrote: > > On Thu, Feb 25, 2016 at 12:05:33PM +0000, Jaydeep Patil wrote: > > > >> +#include <sys/stat.h> > > > >> +struct kernel_stat { > > > >> + unsigned int st_dev; > > > >> + unsigned int __pad1[3]; > > > >> + unsigned long long st_ino; > > > >> + unsigned int st_mode; > > > >> + unsigned int st_nlink; > > > >> + int st_uid; > > > >> + int st_gid; > > > >> + unsigned int st_rdev; > > > >> + unsigned int __pad2[3]; > > > >> + long long st_size; > > > >> + unsigned int st_atime_sec; > > > >> + unsigned int st_atime_nsec; > > > >> + unsigned int st_mtime_sec; > > > >> + unsigned int st_mtime_nsec; > > > >> + unsigned int st_ctime_sec; > > > >> + unsigned int st_ctime_nsec; > > > >> + unsigned int st_blksize; > > > >> + unsigned int __pad3; > > > >> + unsigned long long st_blocks; }; > > > >> + > > > >> +static void __stat_fix(struct kernel_stat *kst, struct stat *st) > > > >> +{ > > > >> + extern void *memset(void *s, int c, size_t n); > > > >> + > > > >> + st->st_dev = kst->st_dev; > > > >> + memset (&st->st_pad1, 0, sizeof (st->st_pad1)); > > > >> + st->st_ino = kst->st_ino; > > > >> + st->st_mode = kst->st_mode; > > > >> + st->st_nlink = kst->st_nlink; > > > >> + st->st_uid = kst->st_uid; > > > >> + st->st_gid = kst->st_gid; > > > >> + st->st_rdev = kst->st_rdev; > > > >> + memset (&st->st_pad2, 0, sizeof (st->st_pad2)); > > > >> + st->st_size = kst->st_size; > > > >> + st->st_pad3 = 0; > > > >> + st->st_atim.tv_sec = kst->st_atime_sec; > > > >> + st->st_atim.tv_nsec = kst->st_atime_nsec; > > > >> + st->st_mtim.tv_sec = kst->st_mtime_sec; > > > >> + st->st_mtim.tv_nsec = kst->st_mtime_nsec; > > > >> + st->st_ctim.tv_sec = kst->st_ctime_sec; > > > >> + st->st_ctim.tv_nsec = kst->st_ctime_nsec; > > > >> + st->st_blksize = kst->st_blksize; > > > >> + st->st_blocks = kst->st_blocks; > > > >> + memset (&st->st_pad5, 0, sizeof (st->st_pad5)); > > > >> + return; > > > >> +} > > > > > > > >You've made this a lot more complicated than it needs to be. Just > > > >copying the __stat_fix code from 32-bit mips should work fine. The > > > >only fixup that needs to be done is for st_dev and st_rdev and it > > > >can be done in-place. > > > > > > In case of MIPS64, the stat syscall returns a structure as described > > > by 'struct kernel_stat'. The ' struct stat' in MIPS64 has following > > > notable difference as compared to 'struct kernel_stat': > > > > > > The st_nlink is of 8 bytes > > > > I missed that in my previous reading. > > > > For all existing archs, nlink_t was the native register size (_Reg) in > > the kernel stat struct. It looks like it's just 32-bit (unsigned int) > > on mips64 though. The clean way to handle this is just moving nlink_t > > back to the per-arch alltypes.h.in files to allow it to vary (or > > actually, just putting a definition in the mips one will override the > > generic one). So in arch/mips64/bits/alltypes.h.in: > > > > TYPEDEF unsigned nlink_t; > > > > > and all st_*tim members are of 16 bytes > > > > Uhg. Does mips64 actually use a 32-bit time_t? If so I think with > > current musl we're stuck as defining time_t as 32-bit, because it's > > used as an interface with all sorts of things in the kernel that we > > don't wrap/control. But this is going to need a lot more review to > > understand if there's any better solution. :( > > > > Even if time_t is 32-bit though, tv_nsec is always long, so the > > kernel's stat structure is broken and needs further fixups like you're > > doing. I don't see any way around this unless there's hope of the > > kernel 64-bit time_t stuff being merged soon, in which case we could > > use that from the beginning on mips64. It feels really awful to add a > > new 64-bit arch with 32-bit time_t. > > > > In light of this I'm not sure it makes sense to try to match the > > kernel's weird nlink_t (see above). > > I've done further reading of what glibc and the kernel do, and it's confusing. > They seem to have 64-bit time_t and just botch it in struct stat which glibc has > to convert from the broken kernel structure to a userspace-facing form. > Looking at the other files in: > > https://sourceware.org/git/?p=glibc.git;a=tree;f=sysdeps/unix/sysv/linux/m > ips/bits;h=c1f9a8df22be6d1c0eb62e20d1113a9f9a11f49a;hb=HEAD > > they seem to use glibc's __time_t in kernel interfaces directly (e.g. > the sysvipc stuff) and from what I can tell the kernel expects a 64-bit > __kernel_time_t in those places, so hopefully this isn't as bad as I intitially > thought. > > > > (due to sizeof long in 64bit). Thus all members of ' struct stat' > > > starting from st_uid are at different offset than what stat syscall > > > has returned. In case of MIPS32, we just need to adjust dev_t (being > > > long long) as described in __stat_fix. However in case of MIPS64 we > > > need to members from 'struct kernel_stat' to 'struct stat' > > > > Yes... > > As long as the time_t definition issue is not in question, I think this is an okay > path to move forward. It might be nice to make nlink_t match whatever glibc > used for it though so that our user-facing struct and glibc's have matching > layout/offsets. > > Sorry for all the confusion over this. > > Rich
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