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[marshal] Add GCUnsafeTransitionBuilder; use for thunk_invoke_wrapper
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Make a "GC Unsafe Transition Builder" - that always calls
mono_threads_attach_coop / mono_threads_detach_coop.

Use it in the native to managed wrappers:
emit_thunk_invoke_wrapper and emit_managed_wrapper

This is a change in behavior for emit_thunk_invoke_wrapper -
previously it directly called
mono_threads_enter_gc_unsafe_region_unbalanced.

That means that compared to the previous behavior, the thunk invoke
wrappers are now a bit more lax: they will be able to be called on
threads that aren't attached to the runtime and they will attach
automatically.

On the other hand existing code will continue to work, with the extra
cost of a check of a thread local var.

Using mono_thread_attach_coop also makes invoke wrappers work
correctly in the interpreter - it special cases
mono_thread_attach_coop but not enter_gc_unsafe.
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@lambdageek
lambdageek committed Feb 10, 2023
1 parent 921cb08 commit 7a55bf0
Showing 1 changed file with 99 additions and 34 deletions.
133 changes: 99 additions & 34 deletions src/mono/mono/metadata/marshal-lightweight.c
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Original file line number Diff line number Diff line change
Expand Up @@ -696,6 +696,87 @@ gc_safe_transition_builder_cleanup (GCSafeTransitionBuilder *builder)
#endif
}

typedef struct EmitGCUnsafeTransitionBuilder {
MonoMethodBuilder *mb;
int orig_domain_var;
int attach_cookie_var;
} GCUnsafeTransitionBuilder;

static void
gc_unsafe_transition_builder_init (GCUnsafeTransitionBuilder *builder, MonoMethodBuilder *mb, gboolean use_attach)
{
g_assert_checked (use_attach);
// Right now we always set use_attach and use mono_threads_coop_attach to enter into gc
// unsafe regions. If !use_attach is needed (ie adding transitions, using
// mono_threads_enter_gc_unsafe_region_unbalanced) that needs to be implemented.
builder->mb = mb;
builder->orig_domain_var = -1;
builder->attach_cookie_var = -1;
}

static void
gc_unsafe_transition_builder_add_vars (GCUnsafeTransitionBuilder *builder)
{
MonoType *int_type = mono_get_int_type ();
builder->orig_domain_var = mono_mb_add_local (builder->mb, int_type);
builder->attach_cookie_var = mono_mb_add_local (builder->mb, int_type);
}

static void
gc_unsafe_transition_builder_emit_enter (GCUnsafeTransitionBuilder *builder)
{
MonoMethodBuilder *mb = builder->mb;
int attach_cookie = builder->attach_cookie_var;
int orig_domain = builder->orig_domain_var;
/*
* // does (STARTING|RUNNING|BLOCKING) -> RUNNING + set/switch domain
* intptr_t attach_cookie;
* intptr_t orig_domain = mono_threads_attach_coop (domain, &attach_cookie);
* <interrupt check>
*/
/* orig_domain = mono_threads_attach_coop (domain, &attach_cookie); */
mono_mb_emit_byte (mb, MONO_CUSTOM_PREFIX);
mono_mb_emit_byte (mb, CEE_MONO_LDDOMAIN);
mono_mb_emit_ldloc_addr (mb, attach_cookie);
/*
* This icall is special cased in the JIT so it works in native-to-managed wrappers in unattached threads.
* Keep this in sync with the CEE_JIT_ICALL code in the JIT.
*
* Special cased in interpreter, keep in sync.
*/
mono_mb_emit_icall (mb, mono_threads_attach_coop);
mono_mb_emit_stloc (mb, orig_domain);

/* <interrupt check> */
emit_thread_interrupt_checkpoint (mb);
}

static void
gc_unsafe_transition_builder_emit_exit (GCUnsafeTransitionBuilder *builder)
{
MonoMethodBuilder *mb = builder->mb;
int orig_domain = builder->orig_domain_var;
int attach_cookie = builder->attach_cookie_var;
/*
* // does RUNNING -> (RUNNING|BLOCKING) + unset/switch domain
* mono_threads_detach_coop (orig_domain, &attach_cookie);
*/

/* mono_threads_detach_coop (orig_domain, &attach_cookie); */
mono_mb_emit_ldloc (mb, orig_domain);
mono_mb_emit_ldloc_addr (mb, attach_cookie);
/* Special cased in interpreter, keep in sync */
mono_mb_emit_icall (mb, mono_threads_detach_coop);
}

static void
gc_unsafe_transition_builder_cleanup (GCUnsafeTransitionBuilder *builder)
{
builder->mb = NULL;
builder->orig_domain_var = -1;
builder->attach_cookie_var = -1;
}

static gboolean
emit_native_wrapper_validate_signature (MonoMethodBuilder *mb, MonoMethodSignature* sig, MonoMarshalSpec** mspecs)
{
Expand Down Expand Up @@ -2253,7 +2334,7 @@ emit_thunk_invoke_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mono
MonoImage *image = get_method_image (method);
MonoMethodSignature *sig = mono_method_signature_internal (method);
int param_count = sig->param_count + sig->hasthis + 1;
int pos_leave, coop_gc_var = 0;
int pos_leave;
MonoExceptionClause *clause;
MonoType *object_type = mono_get_object_type ();
#if defined (TARGET_WASM)
Expand All @@ -2266,6 +2347,10 @@ emit_thunk_invoke_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mono
#else
const gboolean do_blocking_transition = TRUE;
#endif
GCUnsafeTransitionBuilder gc_unsafe_builder = {0,};

if (do_blocking_transition)
gc_unsafe_transition_builder_init (&gc_unsafe_builder, mb, TRUE);

/* local 0 (temp for exception object) */
mono_mb_add_local (mb, object_type);
Expand All @@ -2275,8 +2360,7 @@ emit_thunk_invoke_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mono
mono_mb_add_local (mb, sig->ret);

if (do_blocking_transition) {
/* local 4, the local to be used when calling the suspend funcs */
coop_gc_var = mono_mb_add_local (mb, mono_get_int_type ());
gc_unsafe_transition_builder_add_vars (&gc_unsafe_builder);
}

/* clear exception arg */
Expand All @@ -2285,10 +2369,7 @@ emit_thunk_invoke_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mono
mono_mb_emit_byte (mb, CEE_STIND_REF);

if (do_blocking_transition) {
mono_mb_emit_byte (mb, MONO_CUSTOM_PREFIX);
mono_mb_emit_byte (mb, CEE_MONO_GET_SP);
mono_mb_emit_icall (mb, mono_threads_enter_gc_unsafe_region_unbalanced);
mono_mb_emit_stloc (mb, coop_gc_var);
gc_unsafe_transition_builder_emit_enter (&gc_unsafe_builder);
}

/* try */
Expand Down Expand Up @@ -2361,10 +2442,9 @@ emit_thunk_invoke_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethod *method, Mono
}

if (do_blocking_transition) {
mono_mb_emit_ldloc (mb, coop_gc_var);
mono_mb_emit_byte (mb, MONO_CUSTOM_PREFIX);
mono_mb_emit_byte (mb, CEE_MONO_GET_SP);
mono_mb_emit_icall (mb, mono_threads_exit_gc_unsafe_region_unbalanced);
gc_unsafe_transition_builder_emit_exit (&gc_unsafe_builder);

gc_unsafe_transition_builder_cleanup (&gc_unsafe_builder);
}

mono_mb_emit_byte (mb, CEE_RET);
Expand Down Expand Up @@ -2414,8 +2494,9 @@ static void
emit_managed_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethodSignature *invoke_sig, MonoMarshalSpec **mspecs, EmitMarshalContext* m, MonoMethod *method, MonoGCHandle target_handle, MonoError *error)
{
MonoMethodSignature *sig, *csig;
int i, *tmp_locals, orig_domain, attach_cookie;
int i, *tmp_locals;
gboolean closed = FALSE;
GCUnsafeTransitionBuilder gc_unsafe_builder = {0,};

sig = m->sig;
csig = m->csig;
Expand Down Expand Up @@ -2453,8 +2534,8 @@ emit_managed_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethodSignature *invoke_s
if (MONO_TYPE_ISSTRUCT (sig->ret))
m->vtaddr_var = mono_mb_add_local (mb, int_type);

orig_domain = mono_mb_add_local (mb, int_type);
attach_cookie = mono_mb_add_local (mb, int_type);
gc_unsafe_transition_builder_init (&gc_unsafe_builder, mb, TRUE);
gc_unsafe_transition_builder_add_vars (&gc_unsafe_builder);

/*
* // does (STARTING|RUNNING|BLOCKING) -> RUNNING + set/switch domain
Expand All @@ -2472,21 +2553,7 @@ emit_managed_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethodSignature *invoke_s
mono_mb_emit_icon (mb, 0);
mono_mb_emit_stloc (mb, 2);

/* orig_domain = mono_threads_attach_coop (domain, &attach_cookie); */
mono_mb_emit_byte (mb, MONO_CUSTOM_PREFIX);
mono_mb_emit_byte (mb, CEE_MONO_LDDOMAIN);
mono_mb_emit_ldloc_addr (mb, attach_cookie);
/*
* This icall is special cased in the JIT so it works in native-to-managed wrappers in unattached threads.
* Keep this in sync with the CEE_JIT_ICALL code in the JIT.
*
* Special cased in interpreter, keep in sync.
*/
mono_mb_emit_icall (mb, mono_threads_attach_coop);
mono_mb_emit_stloc (mb, orig_domain);

/* <interrupt check> */
emit_thread_interrupt_checkpoint (mb);
gc_unsafe_transition_builder_emit_enter(&gc_unsafe_builder);

/* we first do all conversions */
tmp_locals = g_newa (int, sig->param_count);
Expand Down Expand Up @@ -2639,11 +2706,9 @@ emit_managed_wrapper_ilgen (MonoMethodBuilder *mb, MonoMethodSignature *invoke_s
}
}

/* mono_threads_detach_coop (orig_domain, &attach_cookie); */
mono_mb_emit_ldloc (mb, orig_domain);
mono_mb_emit_ldloc_addr (mb, attach_cookie);
/* Special cased in interpreter, keep in sync */
mono_mb_emit_icall (mb, mono_threads_detach_coop);
gc_unsafe_transition_builder_emit_exit (&gc_unsafe_builder);

gc_unsafe_transition_builder_cleanup (&gc_unsafe_builder);

/* return ret; */
if (m->retobj_var) {
Expand Down

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