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Date: Wed, 11 May 2016 20:57:12 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Deduplicating __NR_* and SYS_* syscall defines
On Wed, May 11, 2016 at 07:22:30PM -0500, Bobby Bingham wrote:
> On Wed, May 11, 2016 at 05:53:12PM -0400, Rich Felker wrote:
> > On Mon, May 09, 2016 at 07:26:37PM -0500, Bobby Bingham wrote:
> > > During the powerpc64 review, Rich mentioned wanting to replace the
> > > arch/*/bits/syscall.h files with .in files that would be preprocessed with
> > > something like:
> > >
> > > sed -e p -e s/__NR_/SYS_/ < $< > $@
> > >
> > > This would eliminate a lot of intra-file duplication here.
> > >
> > > I took a look, and this won't quite work as-is, because the following
> > > lines in the arm version would end up outputting duplicate definitions:
> > >
> > > #define __ARM_NR_breakpoint 0x0f0001
> > > #define __ARM_NR_cacheflush 0x0f0002
> > > #define __ARM_NR_usr26 0x0f0003
> > > #define __ARM_NR_usr32 0x0f0004
> > > #define __ARM_NR_set_tls 0x0f0005
> >
> > This is easily fixed by something like:
> >
> > sed -e /__NR_/p -e s/__NR_/SYS_/ < $< > $@
>
> Neat. I didn't know about /p.
The p command just prints the pattern space. The trick is that we
print it an extra time before the s command, but only if the line
matches something the s command is going to change.
> Any objection to using Alexander's approach to avoid interleaving the
> __NR_* and SYS_* lines?
I'm indifferent to the interleaving, but if we take that approach, we
should make sure that the rules are written such that interrupting the
make process between the commands doesn't leave a partial file that
subsequent runs of make think is complete. It might be ok as-is if
make automatically deletes the target on error producing it; otherwise
we might need a temp file that's moved into place at the end. I always
forge how this aspect of make works...
> > > Same thing for this line in x32:
> > >
> > > #define __X32_SYSCALL_BIT 0x40000000
> >
> > In general we've tried to eliminate this sort of macro and direct-code
> > the values. I would be in favor of doing the same for x32 I think. But
> > with my fixed sed command (above) I think that change is unnecssary
> > and orthogonal to the deduplication.
>
> I'll submit a separate patch to clean this up.
Any thoughts on how it should be done? If it were a clean decimal
constant like on mips I'd just write each as a single integer literal
(e.g. 6001, etc.) but since the syscall numbers are normally thought
of as decimal whereas the x32 offset is hex/bit value, it seems + or |
is still needed.
> > > I'm thinking something like the following awk script would work:
> > >
> > > {
> > > print
> > > }
> > >
> > > $1 ~ /^#(define|undef)$/ && $2 ~ /^__NR_/ {
> > > sub(/__NR_/, "SYS_", $2)
> > > print
> > > }
> > >
> > > The handling for #undef is for the x32 file. It looks like only the
> > > `#undef __NR_getdents' in that file is actually necessary, and even that
> > > could be avoided by just omitting the earlier line:
> > >
> > > #define __NR_getdents (__X32_SYSCALL_BIT + 78)
> >
> > I don't see why any #undef is needed here; this looks like leftover
> > cruft that was not properly cleaned up. All the logic for replacing
> > syscall numbers belongs in src/internal/syscall.h or
> > arch/$ARCH/syscall_arch.h, I think.
>
> Ok.
Can you verify that removing these #undef-and-redefine lines from the
bits header doesn't change the result (i.e. it's redundant with other
files) for building libc?
> > > So maybe we can get rid of the #undefs there, and simplify the awk script
> > > accordingly.
> > >
> > > Thoughts on this approach? If this sounds ok, I'll submit a patch.
> >
> > I'd rather use sed than awk if possible since it's more universally
> > available and understood.
>
> I must be the exception then :)
:-)
Rich
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