On Sat, Sep 02, 2017 at 08:18:00AM +0000, Daniel Shahaf wrote: > [replying to multiple] > > James McCoy wrote on Fri, Sep 01, 2017 at 08:15:05 -0400: > > On Fri, Sep 01, 2017 at 03:07:16AM +0000, Daniel Shahaf wrote: > > > I'm not sure I'm getting through here. > > > > > > The note does say "Don't allocate one of these yourself" but in the > > > second sentence implies that the reason for this is that if you allocate > > > it yourself and don't initialize all pointer-to-function members, > > > Trouble will ensue. Therefore, the note could be construed as meaning > > > that it is okay to allocate one of these yourself if you take care to > > > initialize all pointer members. > > > > The fact that a user can choose not to use the recommended API doesn't > > mean that there is an ABI break. A user can already choose to allocate > > the structure themselves and not initialize everything. Adding an item > > to the struct doesn't change that. > > > > I'm afraid I don't follow. If a user allocates the struct themselves > and doesn't initialize all members, then (1) they are in violation of > the API's precondition, (2) their code will (depending on the repository > data) dereference an uninitialized pointer-to-function at runtime. > That's undefined behaviour de jure and some form of crash de facto.
Right, but it's not an ABI break. It's misuing the API. > > I ran abi-compliance-checker[0] against the head of branches/1.9.x and > > trunk. It shows no incompatibility issues. The report is attached for > > anyone that wants to view it. > > > > [0]: http://ispras.linuxbase.org/index.php/ABI_compliance_checker > > Thanks for adding this datapoint, but, how does it support your > argument? The checker's output confirms what we already knew without > it: that adding a member to a struct type can result in breakage when > code compiled against 1.9 is run against 1.10 without rebuilding: It confirms that there's not an ABI break. Code that's misuing the API can break, yes, but not code that's using the API correctly. Cheers, -- James GPG Key: 4096R/91BF BF4D 6956 BD5D F7B7 2D23 DFE6 91AE 331B A3DB
