[ctor-eval] Add an option to keep some exports (#4441)

By default wasm-ctor-eval removes exports that it manages to completely
eval (if it just partially evals then the export remains, but points to a function
with partially-evalled contents). However, in some cases we do want to keep
the export around even so, for example during fuzzing (as the fuzzer wants
to call the same exports before and after wasm-ctor-eval runs) and also
if there is an ABI we need to preserve (like if we manage to eval all of
main()), or if the function returns a value (which we don't support yet, but
this is a PR to prepare for that).

Specifically, there is now a new option:

--kept-exports foo,bar

That is a list of exports to keep around.

Note that when we keep around an export after evalling the ctor we
make the export point to a new function. That new function just
contains a nop, so that nothing happens when it is called. But the
original function is kept around as it may have other callers, who we
do not want to modify.

1 files changed, 2 insertions, 0 deletions

diff --git a/auto_update_tests.py b/auto_update_tests.py
index 9f93142a8..7277f5e77 100755
--- a/auto_update_tests.py
+++ b/auto_update_tests.py
@@ -89,6 +89,8 @@ def update_ctor_eval_tests():
         cmd = shared.WASM_CTOR_EVAL + [t, '-all', '-o', 'a.wast', '-S', '--ctors', ctors]
         if 'ignore-external-input' in t:
             cmd += ['--ignore-external-input']
+        if 'results' in t:
+            cmd += ['--kept-exports', 'test1,test3']
         support.run_command(cmd)
         actual = open('a.wast').read()
         out = t + '.out'