[Guile-commits] 02/03: Refactor relationship between gc_mutator_roots and threads

[Andy Wingo]

wingo pushed a commit to branch wip-whippet
in repository guile.

commit 75f1f20031264c226085b98352b229fd58d4b036
Author: Andy Wingo <wi...@pobox.com>
AuthorDate: Wed Jul 2 21:33:12 2025 +0200

    Refactor relationship between gc_mutator_roots and threads
    
    * libguile/threads.c (guilify_self_1):
    * libguile/whippet-embedder.h (gc_trace_mutator_pinned_roots): Make the
    roots contain the thread.  This way sizeof(*thread) is the total
    allocation size; if you pad the allocation with extra words, some of the
    self-checks in nofl get borked.
---
 libguile/threads.c          | 14 +++-----------
 libguile/whippet-embedder.h |  4 ++--
 2 files changed, 5 insertions(+), 13 deletions(-)

diff --git a/libguile/threads.c b/libguile/threads.c
index 85ccc7a57..ee3e6cc63 100644
--- a/libguile/threads.c
+++ b/libguile/threads.c
@@ -359,22 +359,15 @@ static int thread_count;
 
 static SCM default_dynamic_state;
 
-struct scm_thread_and_roots
-{
-  struct scm_thread thread;
-  struct gc_mutator_roots roots;
-};
-
 /* Perform first stage of thread initialisation, in non-guile mode.
  */
 static void
 guilify_self_1 (struct gc_mutator *mut, struct gc_stack_addr base,
                 int needs_unregister)
 {
-  struct scm_thread_and_roots *thread_and_roots =
-    gc_allocate (mut, sizeof (*thread_and_roots), GC_ALLOCATION_TAGGED);
-  scm_thread *t = &thread_and_roots->thread;
-  struct gc_mutator_roots *roots = &thread_and_roots->roots;
+  struct gc_mutator_roots *roots =
+    gc_allocate (mut, sizeof (*roots), GC_ALLOCATION_TAGGED);
+  scm_thread *t = &roots->thread;
 
   /* We'll be referring to this object from thread-locals and other
      places that are gnarly to relocate.  */
@@ -410,7 +403,6 @@ guilify_self_1 (struct gc_mutator *mut, struct 
gc_stack_addr base,
   scm_i_current_thread = t;
 #endif
 
-  roots->thread = t;
   gc_mutator_set_roots (mut, roots);
 
   scm_i_pthread_mutex_lock (&thread_admin_mutex);
diff --git a/libguile/whippet-embedder.h b/libguile/whippet-embedder.h
index bd6c9f934..e09f017f5 100644
--- a/libguile/whippet-embedder.h
+++ b/libguile/whippet-embedder.h
@@ -39,7 +39,7 @@
 
 struct scm_thread;
 struct gc_mutator_roots {
-  struct scm_thread *thread;
+  struct scm_thread thread;
 };
 
 #define GC_EMBEDDER_EPHEMERON_HEADER uintptr_t tag;
@@ -129,7 +129,7 @@ gc_trace_mutator_pinned_roots (struct gc_mutator_roots 
*roots,
                                                         void *trace_data),
                                struct gc_heap *heap,
                                void *trace_data) {
-  scm_trace_thread_roots (roots->thread, trace_pinned, trace_ambiguous,
+  scm_trace_thread_roots (&roots->thread, trace_pinned, trace_ambiguous,
                           heap, trace_data);
 }