>>> On 16.07.14 at 17:19, <dzic...@redhat.com> wrote: > Hi Jan, Michal, > > I am not sure who maintains genksyms officially, so I am sending this > question to the two of you as folks who seemed to have contributed to the > tool. :-) > > I noticed with genksyms that a symbol is opaquely defined in a > public header file (on purpose) and then fully defined in a private > header. This is normal practice. Further, symbol checksumming is done on > EXPORT_SYMBOLs in a private c file that includes the private header > files. > > As a result, even though a struct symbol is intentionally opaquely defined > in a public header file consumed by a third party module, the symbol > checksumming still includes the full definition (because the private c > file with the actual export symbol has the full definition). This has > made it difficult to modify the private header file struct because it > breaks the symbol checksumming. > > For example, let's consider > > block/blk-core.c:EXPORT_SYMBOL(blk_put_queue); > > blk_put_queue will eventually depend on struct blkcq_gq. > > Now publicly blkcg_gq is defined opaquely in > > include/linux/blkdev.h > > and privately in > > block/block-cgroup.h > > Now when we checksum blk_put_queue both include/linux/blkdev.h and > block/block-cgroup.h are included in block/blk-core.c, so blkcg_gq is > fully defined for checksumming. > > Later if we modify blkcq_gq in block/block-cgroup.h the checksum changes, > even though it can debated that block-cgroup.h is a private header file > and it should not impact kabi for third party modules. > > Have either of you run into this? Or is the argument that private files > should not impact the checksum not as strong as I might think? Or is it a > technical problem of how to separate the public includes from the private > includes in the preprocessed file?
Yes, I think we've run into this (if not elsewhere then by seeing [and having to wave] false positive kABI changes). Besides being a technical problem of separating one kind of header from the other, I'm also unsure whether uniformly ignoring definitions in private headers would always be correct. Hence I think a possible solution to this ought to involve manual annotation of structures not to participate in CRC calculations. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
