On Fri, Aug 1, 2014 at 6:16 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > Actually, sadly, while that worked for my test-cases (and for Josh's > case), it turns out to really *not* work in general: the dummy > EXPR_IDENTIFIER that we create may end up referring to a unnamed > union, which doesn't *have* an ident associated with it. > > This only really triggers when you mix named initializers with then > relying on the whole "initialize the next one without a name", but > that does happen. And it fundamentally breaks that whole "use > find_identifier()" approach. > > So convert_ident() really cannot use find_indent(), and really does > have to use "sym->offset". But that doesn't work for anonymous union > members, because that offset was the offset within the anonymous > union, not the parent structure. > > However, the fix is "simple". We can just say that anonymous > union/structure member offsets have to be the offsets within the > parent union instead, and fix things up. So how about a patch like > this *instead* of the previous patch.. Sorry I am late for the party. This approach assume the anonymous structure is only referenced inside the structure. There is not other external reference. However, that assumption is not true if "-fplan9-extensions" or "-fms-extensions" was enabled. Sparse current does not support these two extensions. But it will be a problem if we support them down the road. According to this gcc document: https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html One of the example is this: struct s1 { int a; }; struct s2 { struct s1; }; You see, "struct s1" does not have a name, however "struct s1" can be referenced from other symbol. So update the symbol offset in "struct s1" will be wrong for the other reference of "struct s1". Actually, the "find_identifier" call inside function "check_designators" already calculate the correct offset. Only if we can pass that offset to "convert_ident()". Another idea is that, instead of using ident in EXPR_IDENTIFIER, we can do one time find_identifier(). Then convert the EXPR_IDENTIFIER to an index to the struct. It might take more than one index level for the anonymous struct or union. BTW, that is very similar to the LLVM performing the "Get Element Pointer" instruction. Using the index, we can still reference the anonymous struct. This is not a trivial change. However it might be the right thing to do if we want to support "-fplan9-extensions" Chris -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
