Hi Mike, On 03/11/2017 08:54 PM, Mike Frysinger wrote: > Architectures that split 64-bit values across registers pairs usually do > so according to their C ABI calling convention (which means endianness). > Add some notes to that effect, and change the readahead example to show > a little endian example (since that is way more common than big endian). Thanks. You're a star. I was going to ask you if you might right a patch, since I thought you'd do it better than me! > Also start a new list of syscalls that this issue does not apply to. And thanks also for adding that. > Signed-off-by: Mike Frysinger <vapier@xxxxxxxxxx> > --- > v2 > - add preadv/prwritev/preadv2/prwritev2 to the new list. > > man2/syscall.2 | 22 ++++++++++++++++++++-- > 1 file changed, 20 insertions(+), 2 deletions(-) > > diff --git a/man2/syscall.2 b/man2/syscall.2 > index fcb0a7e21248..f8c89b84356d 100644 > --- a/man2/syscall.2 > +++ b/man2/syscall.2 > @@ -102,13 +102,14 @@ Thus, using > instead of the wrapper provided by glibc, > the > .BR readahead () > -system call would be invoked as follows on the ARM architecture with the EABI: > +system call would be invoked as follows on the ARM architecture with the EABI > +in little endian mode: > > .in +4n > .nf > syscall(SYS_readahead, fd, 0, > - (unsigned int) (offset >> 32), > (unsigned int) (offset & 0xFFFFFFFF), > + (unsigned int) (offset >> 32), > count); > .fi > .in > @@ -124,6 +125,8 @@ register pair. > That means inserting a dummy value into > .I r1 > (the second argument of 0). > +Care also must be taken so that the split follows endian conventions > +(according to the C ABI for the platform). > > Similar issues can occur on MIPS with the O32 ABI, > on PowerPC with the 32-bit ABI, and on Xtensa. > @@ -140,6 +143,21 @@ The affected system calls are > .BR sync_file_range (2), > and > .BR truncate64 (2). > + > +.\" You need to look up the syscalls directly in the kernel source to see if > +.\" they should be in this list. For example, look at fs/read_write.c and > +.\" the function signatures that do: > +.\" ..., unsigned long, pos_l, unsigned long, pos_h, ... > +.\" If they use off_t, then they most likely do not belong in this list. Thanks for adding the above comment in the source. That sort of stuff is hugely helpful for me when I come to revisit this sometime in the future when I've already forgotten this discussion. > +This does not affect syscalls that manually split and assemble 64-bit values > +such as > +.BR _llseek (2), > +.BR preadv (2), > +.BR preadv2 (2), > +.BR pwritev (2). > +and > +.BR pwritev2 (2). > +Welcome to the wonderful world of historical baggage. > .SS Architecture calling conventions > Every architecture has its own way of invoking and passing arguments to the > kernel. Patch applied. Thanks! Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
