Re: Deduplicating __NR_* and SYS_* syscall defines

[Rich Felker <dalias@libc.org>]

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_/ < $< > $@

> 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'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.

> 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.

Rich