[RFT] syscall: set default constants for Inline::C platforms

[Eric Wong <e@80x24.org>]

Gaelan Steele <gaelans@icloud.com> wrote:
> Unfortunately this patch broke public-inbox on Darwin:
> 
> Bareword "SIZEOF_cmsghdr" not allowed while "strict subs" in use at /tmp/public-inbox/lib/PublicInbox/Syscall.pm line 456.
> BEGIN not safe after errors--compilation aborted at /tmp/public-inbox/lib/PublicInbox/Syscall.pm line 460.
> Compilation failed in require at /tmp/public-inbox/lib/PublicInbox/DS.pm line 31.
> BEGIN failed--compilation aborted at /tmp/public-inbox/lib/PublicInbox/DS.pm line 32.
> Compilation failed in require at /tmp/public-inbox/lib/PublicInbox/Daemon.pm line 17.
> BEGIN failed--compilation aborted at /tmp/public-inbox/lib/PublicInbox/Daemon.pm line 17.
> Compilation failed in require at /tmp/public-inbox/script/public-inbox-httpd line 7.
> BEGIN failed--compilation aborted at /tmp/public-inbox/script/public-inbox-httpd line 7.
> 
> I’m not enough of a Perl person to fully untangle this. As
> best I can tell, the intent is that non-Linux/BSD OSes should
> still work with Inline::C, but this doesn’t work in practice
> due to a bug?

Right.  Patch below should fix it, test feedback appreciated.

> It may also be possible to use the BSD approach on Darwin -
> Darwin ascribes to the BSD school of thought where libc is the
> only Officially Stable interface, but if you can get away with
> it on the real BSDs maybe you can get away with it on fake BSD
> too.

NetBSD and FreeBSD both document the underlying syscall numbers
remain stable (but not the name => number mapping).  OpenBSD has
no stable numbering, but goes as far as to patch Perl to route
the `syscall' perlop through their libc to avoid breaking Perl
scripts.

I have no idea if Darwin maintains any stability guarantees at
all like the above OSes, so Inline::C may be safer, here.

-------8<-------
Subject: [PATCH] syscall: set default constants for Inline::C platforms

This ought to fix compile errors on platforms we don't
explicitly support.

Reported-by: Gaelan Steele <gaelans@icloud.com>
---
 lib/PublicInbox/Syscall.pm | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/PublicInbox/Syscall.pm b/lib/PublicInbox/Syscall.pm
index 829cfa3c..99af5bf5 100644
--- a/lib/PublicInbox/Syscall.pm
+++ b/lib/PublicInbox/Syscall.pm
@@ -317,6 +317,10 @@ BEGIN {
 		)
 	}
 	$PACK{CMSG_ALIGN_size} = SIZEOF_size_t;
+	$PACK{SIZEOF_cmsghdr} //= 0;
+	$PACK{TMPL_cmsg_len} //= undef;
+	$PACK{CMSG_DATA_off} //= undef;
+	$PACK{TMPL_msghdr} //= undef;
 }
 
 # SFD_CLOEXEC is arch-dependent, so IN_CLOEXEC may be, too