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Make try_init_allocator() a ctor #338

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Make try_init_allocator() a ctor #338

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9 changes: 1 addition & 8 deletions dlmalloc/src/malloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4562,7 +4562,7 @@ static void* tmalloc_small(mstate m, size_t nb) {

#if __wasilibc_unmodified_upstream // Forward declaration of try_init_allocator.
#else
static void try_init_allocator(void);
__attribute__((constructor(0))) static void try_init_allocator(void);
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The entire range of 0-100 I believe is reserved for system functions like this. I'm not convinced 0 is the best choice here, but its not not hard to change in the future.

In emscripten we document the priorities in order to keep track of all the order which this stuff happens: https://github.com/emscripten-core/emscripten/blob/main/system/lib/README.md?plain=1#L9-L28

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Practically speaking, right now whenever we add a new constructor in wasi-libc, we just grep for all the constructors in the wasi-libc tree to figure out the ordering constraints, which seems ok for now, as there aren't very many.

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I believe assigning priority 0 is a correct choice, given:

  • dlmalloc is a service which is likely used by other ctors
  • try_init_allocator itself doesn't rely on other ctors to be run before

We can also have a documentation somewhere to list all our ctors. I can add one in this PR if you folks think it's appropriate, though not sure where's the best place to add it.

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I think its ok to simply use grep as Dan says, I was just pointing out that it can get complicated, and that one needs to be careful when choosing the order of these things, once there is more than one.

There are also some things that might (one day) need to happen before malloc initialization (e.g. TLS setup, application of relocations in PIC code) although I don't think any of those apply yet in wasi-libc.

#endif

void* dlmalloc(size_t bytes) {
Expand Down Expand Up @@ -4593,13 +4593,6 @@ void* dlmalloc(size_t bytes) {
ensure_initialization(); /* initialize in sys_alloc if not using locks */
#endif

#if __wasilibc_unmodified_upstream // Try to initialize the allocator.
#else
if (!is_initialized(gm)) {
try_init_allocator();
}
#endif

if (!PREACTION(gm)) {
void* mem;
size_t nb;
Expand Down