Fix out-of-bounds dltab in the WASI dlopen shim - #86
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dltab was a tentative one-element array ("dict_t* dltab[]") indexed past
its end, and slot 0 was never assigned: the first library was stored at
dltab[1] while the lookup loop read dltab[0..dltab_index). Every dlopen
lookup therefore dereferenced a NULL dict, i.e. guest address 0.
That happens to be harmless while address 0 holds zeros (the dict's len
field reads as 0), which is why the socket-file transport never noticed.
With the CMA wire channel, live request bytes sit at the bottom of linear
memory, so the NULL-dict read picks up garbage lengths and entry pointers
and traps — reproducible as a crash on the first CREATE EXTENSION issued
over CMA.
Make dltab a real fixed-size array, keep every slot initialized, check
the existing-library branch against index >= 0 (slot 0 is valid), and
return stable 1-based handles.
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The WASI dlopen shim's library table (
dltabinwasm-build/sdk_port-wasi/sdk_port-wasi-dlfcn.c) is a tentative one-element array indexed past its end, and slot 0 is never assigned — the first library is stored atdltab[1]while the lookup loop readsdltab[0..dltab_index). Every lookup therefore dereferences a NULL dict, i.e. guest address 0.This is invisible with the socket-file transport (address 0 holds zeros, so the dict's
lenreads as 0 and the loop is skipped), but with the CMA wire channel live request bytes sit at the bottom of linear memory, so the NULL-dict read picks up garbage lengths/pointers and traps. Reproducible as a crash on the firstCREATE EXTENSIONissued over CMA.This PR makes
dltaba real fixed-size array, keeps every slot initialized, fixes the existing-library check (>= 0— index 0 is a valid hit), and returns stable 1-based handles.Found while building a native (wasm2c) iOS embedding of this branch — https://github.com/bendytree/pglite-ios — where the fix is verified by test suites on macOS, iOS simulator, and iPhone hardware.