On Mon, Jan 02, 2017 at 07:15:30PM +0100, Andrea Bolognani wrote:
Clang 3.9 refuses to compile the existing code with the
following error:
util/virfirewall.c:425:20: error: passing an object that undergoes
default argument promotion to 'va_start'
has undefined behavior [-Werror,-Wvarargs]
va_start(args, layer);
^
util/virfirewall.c:420:37: note: parameter of type 'virFirewallLayer'
is declared here
virFirewallLayer layer,
^
This happens because 'layer' is of type virFirewallLayer, which
is an enum type and not a standard type such as eg. void* or int.
To solve the issue, turn virFirewallAddRule() from a very thin
wrapper around virFirewallAddRuleFullV() to a macro that expands
to a call to virFirewallAddRuleFull() - itself a very thin wrapper
around the aforementioned virFirewallAddRuleFullV() - with no loss
of functionality or type safety.
---
This only seems to be required on very specific combinations
of Clang and host OS, eg. I need it on Clang 3.9 / Fedora
rawhide but not on Clang 3.8 or 4.0 / Debian sid.
We sent various patches for this (me, Jan and maybe other people as well). I never realized it's not a problem with different versions of clang. I would say it's not a problem for us to solve it in this case, however, as I wrote in my solution, it works, but it's undefined from the specification point of view. Can it work just because virFirewallAddRule() gets optimized into inline function? it shouldn't be, though... I don't know.
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