Date: Fri, 13 May 2016 12:02:19 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: Deduplicating __NR_* and SYS_* syscall defines On Fri, May 13, 2016 at 12:15:48PM +0200, Szabolcs Nagy wrote: > * Rich Felker <dalias@...c.org> [2016-05-11 20:57:12 -0400]: > > 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 don't know how much is it worth to keep the syntax consistent > with kernel headers, i'd just clean these up with special syntax > like TYPEDEF in alltypes e.g. > > SYS write 1 This does save some space (maybe 25-30% size reduction?) but I think it also comes at the sense of some flexibility and readability. For example if there are ever archs where the definitions need to depend on some compile-time macros (e.g. if we had an arch where it makes sense to put a couple ABI variants with different syscalls together as subarchs rather than independent archs) there becomes a question of how to format those conditions and whether their directives would be misinterpreted. Having #define on every line so that the file as-is is valid preprocessor input avoids any such issues. Of course these things are also a reason to possibly prefer the form with SYS_ and __NR_ interleaved (my original sed command). With them separate like the current proposed patch, anything inside a conditional block or dependent on interleaved redefinition of other macros would break. > with consistent whitespace, removed comments etc. Agree on consistent whitespace (and we should do that regardless of the rest of this proposal), but note that it can't necessarily be just 3 space-delimited tokens. Some archs have arithmetic expressions for the integer field, and requiring that not to contain whitespace would be rather arbitrary and confusing, so the last field would probably need to be the whole remainder of the line. Rich
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