Re: Deduplicating __NR_* and SYS_* syscall defines

[Bobby Bingham <koorogi@koorogi.info>]

On Wed, May 11, 2016 at 08:57:12PM -0400, Rich Felker wrote:
> 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...

Make does what you want by default.

https://www.gnu.org/software/make/manual/html_node/Interrupts.html

> 
> > > > 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 agree.  I was planning to use +.

> 
> > > > 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?

I just verified, the generated code for libc is the same either way.

> 
> > > > 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