[PATCH] D38846: [ELF] - Linkerscript: fix issue with SUBALIGN.

[Rui Ueyama via Phabricator via llvm-commits]

ruiu added a comment.

You should distinguish two completely different things. As to an expression you can use within SUBALIGN(<expr>), we are not too picky about terms, functions or operators you can use in the expression. It is something like C allows you to shoot your foot with `i = i++`. As long as <expr> in SUBALIGN(<expr>) returns some value, we don't care how it is computed. We just use it.

However, an attempt to set a non-power-of-two value to an alignment is a completely different story, because we assume everywhere in our code base that alignments are always power of two. If you break that assumption, the entire linker's behavior becomes unpredictable. It may work, or it may crash. The point is, we don't want to fall into that situation. We need to protect ourselves from bad inputs that breaks our internal assumptions.

So, that's different, and you should check for an input value if it is a power of two.

(Also, speaking of 0, since 0 means 1 in this context, it is a power of two because it is actually 1.)


https://reviews.llvm.org/D38846