I don't think the approach of making a call from inline asm is safe. In particular, it clobbers the redzone [1], which the compiler may have used and expect to be intact after the call.
In general, at least some compilers (e.g., gcc) assume there are no calls in an inline asm block.
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Even then, I am not quite sure: redzone is just an example of one of the assumptions that might be violated when calls are made from an asm block, but at least some gcc devs are on record saying that calls from inline asm are not supported: the main problem is that leaf functions can be compiled differently than non-leaf, and a hidden call breaks this (i.e., a non-leaf function may appear as leaf to the compiler).
Note that one way to get the code size wins for the caller in a compiler-blessed way is to use an alternative calling convention, like Clang's preserve_most; this isn't as good as explicitly providing a clobber list, but allows a library to provide a stable interface.