[Git][ghc/ghc][wip/initializers] rts: Refactor unloading of foreign export StablePtrs
Ben Gamari
gitlab at gitlab.haskell.org
Wed Sep 16 18:05:36 UTC 2020
Ben Gamari pushed to branch wip/initializers at Glasgow Haskell Compiler / GHC
Commits:
40aaa8a2 by Ben Gamari at 2020-09-16T14:05:29-04:00
rts: Refactor unloading of foreign export StablePtrs
Previously we would allocate a linked list cell for each foreign export.
Now we can avoid this by taking advantage of the fact that they are
already broken into groups.
- - - - -
4 changed files:
- includes/rts/ForeignExports.h
- rts/ForeignExports.c
- rts/Linker.c
- rts/LinkerInternals.h
Changes:
=====================================
includes/rts/ForeignExports.h
=====================================
@@ -29,6 +29,8 @@ struct ForeignExportsList {
/* if the RTS linker loaded the module,
* this points to an array of length ->n_entries
* recording the StablePtr for each export. */
+ StgStablePtr **stable_ptrs;
+ /* the exported closures. of length ->exports. */
StgPtr exports[];
};
=====================================
rts/ForeignExports.c
=====================================
@@ -48,12 +48,14 @@ static ObjectCode *loading_obj = NULL;
* For instance, doing exactly this resulted in #18548.
*
* Another consideration here is that the linker needs to know which
- * `StablePtr`s belong to each `ObjectCode` it loads for the sake of unloading.
- * For this reason, the linker informs us when it is loading an object by calling
- * `foreignExportsLoadingObject` and `foreignExportsFinishedLoadingObject`. We
- * take note of the `ObjectCode*` we are loading in `loading_obj` such that we
- * can associate the `StablePtr` with the `ObjectCode` in
- * `processForeignExports`.
+ * `StablePtr`s belong to each `ObjectCode` so it can free them when the module is
+ * unloaded. For this reason, the linker informs us when it is loading an
+ * object by calling `foreignExportsLoadingObject` and
+ * `foreignExportsFinishedLoadingObject`. We take note of the `ObjectCode*` we
+ * are loading in `loading_obj` such that we can associate the `ForeignExportsList` with
+ * the `ObjectCode` in `processForeignExports`. We then record each of the
+ * StablePtrs we create in the ->stable_ptrs array of ForeignExportsList so
+ * they can be enumerated during unloading.
*
*/
@@ -94,20 +96,35 @@ void foreignExportsFinishedLoadingObject()
void processForeignExports()
{
while (pending) {
- for (int i=0; i < pending->n_entries; i++) {
- StgPtr p = pending->exports[i];
- StgStablePtr *sptr = getStablePtr(p);
+ struct ForeignExportsList *cur = pending;
+ pending = cur->next;
- if (loading_obj != NULL) {
- ForeignExportStablePtr *fe_sptr = (ForeignExportStablePtr *)
- stgMallocBytes(sizeof(ForeignExportStablePtr),
- "foreignExportStablePtr");
- fe_sptr->stable_ptr = sptr;
- fe_sptr->next = loading_obj->stable_ptrs;
- pending->oc->stable_ptrs = fe_sptr;
+ /* sanity check */
+ ASSERT(cur->stable_ptrs == NULL);
+
+ /* N.B. We only need to populate the ->stable_ptrs
+ * array if the object might later be unloaded.
+ */
+ if (cur->oc != NULL) {
+ cur->stable_ptrs =
+ stgMallocBytes(sizeof(StgStablePtr*) * cur->n_entries,
+ "foreignExportStablePtr");
+
+ for (int i=0; i < cur->n_entries; i++) {
+ StgStablePtr *sptr = getStablePtr(cur->exports[i]);
+
+ if (cur->oc != NULL) {
+ cur->stable_ptrs[i] = sptr;
+ }
+ }
+ cur->next = cur->oc->foreign_exports;
+ cur->oc->foreign_exports = cur;
+ } else {
+ /* can't be unloaded, don't bother populating
+ * ->stable_ptrs array. */
+ for (int i=0; i < cur->n_entries; i++) {
+ getStablePtr(cur->exports[i]);
}
}
-
- pending = pending->next;
}
}
=====================================
rts/Linker.c
=====================================
@@ -1239,14 +1239,18 @@ static void freeOcStablePtrs (ObjectCode *oc)
{
// Release any StablePtrs that were created when this
// object module was initialized.
- ForeignExportStablePtr *fe_ptr, *next;
+ struct ForeignExportsList *exports, *next;
- for (fe_ptr = oc->stable_ptrs; fe_ptr != NULL; fe_ptr = next) {
- next = fe_ptr->next;
- freeStablePtr(fe_ptr->stable_ptr);
- stgFree(fe_ptr);
+ for (exports = oc->foreign_exports; exports != NULL; exports = next) {
+ next = exports->next;
+ for (int i = 0; i < exports->n_entries; i++) {
+ freeStablePtr(exports->stable_ptrs[i]);
+ }
+ stgFree(exports->stable_ptrs);
+ exports->stable_ptrs = NULL;
+ exports->next = NULL;
}
- oc->stable_ptrs = NULL;
+ oc->foreign_exports = NULL;
}
static void
@@ -1404,7 +1408,7 @@ mkOc( pathchar *path, char *image, int imageSize,
oc->n_segments = 0;
oc->segments = NULL;
oc->proddables = NULL;
- oc->stable_ptrs = NULL;
+ oc->foreign_exports = NULL;
#if defined(NEED_SYMBOL_EXTRAS)
oc->symbol_extras = NULL;
#endif
=====================================
rts/LinkerInternals.h
=====================================
@@ -135,17 +135,6 @@ typedef struct _Segment {
int n_sections;
} Segment;
-/*
- * We must keep track of the StablePtrs that are created for foreign
- * exports by constructor functions when the module is loaded, so that
- * we can free them again when the module is unloaded. If we don't do
- * this, then the StablePtr will keep the module alive indefinitely.
- */
-typedef struct ForeignExportStablePtr_ {
- StgStablePtr stable_ptr;
- struct ForeignExportStablePtr_ *next;
-} ForeignExportStablePtr;
-
#if defined(powerpc_HOST_ARCH) || defined(x86_64_HOST_ARCH)
#define NEED_SYMBOL_EXTRAS 1
#endif
@@ -240,7 +229,8 @@ typedef struct _ObjectCode {
char* bssBegin;
char* bssEnd;
- ForeignExportStablePtr *stable_ptrs;
+ /* a list of all ForeignExportsLists owned by this object */
+ struct ForeignExportsList *foreign_exports;
/* Holds the list of symbols in the .o file which
require extra information.*/
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/40aaa8a26ec610bc652847c936fe0a511faeb0a7
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/40aaa8a26ec610bc652847c936fe0a511faeb0a7
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