Avoid trampolines in emmalloc #20496
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| #define EMMALLOC_ALIAS(ALIAS, ORIGINAL) | ||
| #else | ||
| #define EMMALLOC_EXPORT __attribute__((weak, __visibility__("default"))) | ||
| #define EMMALLOC_ALIAS(ALIAS, ORIGINAL) extern __typeof(ORIGINAL) ALIAS __attribute__((alias(#ORIGINAL))); | ||
| #define EMMALLOC_ALIAS(ALIAS, ORIGINAL) extern __typeof(ORIGINAL) ALIAS __attribute__((weak, alias(#ORIGINAL))); |
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Why do we need to make these weak?
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This is to match the previous behavior.
If we don't do this then e.g. malloc would not be weak, so the user couldn't override it.
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I'm not sure that it true though.. the existing symbols are strong in that if you link the object file you are forced to take that definition. Do you have a test that fails without weak?
Overriding malloc as far as I know only works today if you don't actually use any symbols from emmalloc.o (or dlmalloc.o).
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Oh sorry. I see the existing EMMALLOC_EXPORT is weak... I'm not sure it should be but lgtm given that
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Also dlmalloc.c uses weak aliases for all of these..
Rather than define
mallocas a small function that callsemmalloc_malloc, just make itan alias.
In an optimized build the small functions get inlined away, but we can save that work,
and also it can have downsides (e.g. they have different function pointers, which
aliases do not, see discussion in #20487).
For that to work, we need to make the aliases weak. I think that might have been the
reason to not do this beforehand, but it seems to work ok.