From 57409244ec8f568ce6b4ecb1bde0e509942ac05f Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Thu, 24 Jun 2021 18:02:51 +0200
Subject: [PATCH] boehmgc: Crude support for coroutines
Fixes the problem where a stack pointer outside the original
thread causes the collector to crash.
It could be made more accurate by recording the stack pointer
every time we switch to a coroutine. We can use this information
to update our own coroutine stacks like normal data. When the
stack pointer is on a thread, we can add a field to GC_thread
"fallback_sp" to be used when the thread sp is outside the original
thread range.
---
boehmgc-coroutine-sp-fallback.diff | 44 ++++++++++++++++++++++++++++++
flake.nix | 8 +++++-
2 files changed, 51 insertions(+), 1 deletion(-)
create mode 100644 boehmgc-coroutine-sp-fallback.diff
diff --git a/boehmgc-coroutine-sp-fallback.diff b/boehmgc-coroutine-sp-fallback.diff
new file mode 100644
index 000000000..c618718a7
--- /dev/null
+++ b/boehmgc-coroutine-sp-fallback.diff
@@ -0,0 +1,44 @@
+diff --git a/pthread_stop_world.c b/pthread_stop_world.c
+index 1cee6a0b..8977b0dd 100644
+--- a/pthread_stop_world.c
++++ b/pthread_stop_world.c
+@@ -674,6 +674,8 @@ GC_INNER void GC_push_all_stacks(void)
+ struct GC_traced_stack_sect_s *traced_stack_sect;
+ pthread_t self = pthread_self();
+ word total_size = 0;
++ size_t stack_limit;
++ pthread_attr_t pattr;
+
+ if (!EXPECT(GC_thr_initialized, TRUE))
+ GC_thr_init();
+@@ -723,6 +725,30 @@ GC_INNER void GC_push_all_stacks(void)
+ hi = p->altstack + p->altstack_size;
+ /* FIXME: Need to scan the normal stack too, but how ? */
+ /* FIXME: Assume stack grows down */
++ } else {
++ if (pthread_getattr_np(p->id, &pattr)) {
++ ABORT("GC_push_all_stacks: pthread_getattr_np failed!");
++ }
++ if (pthread_attr_getstacksize(&pattr, &stack_limit)) {
++ ABORT("GC_push_all_stacks: pthread_attr_getstacksize failed!");
++ }
++ // When a thread goes into a coroutine, we lose its original sp until
++ // control flow returns to the thread.
++ // While in the coroutine, the sp points outside the thread stack,
++ // so we can detect this and push the entire thread stack instead,
++ // as an approximation.
++ // We assume that the coroutine has similarly added its entire stack.
++ // This could be made accurate by cooperating with the application
++ // via new functions and/or callbacks.
++ #ifndef STACK_GROWS_UP
++ if (lo >= hi || lo < hi - stack_limit) { // sp outside stack
++ lo = hi - stack_limit;
++ }
++ #else
++ if (lo < hi || lo >= hi + stack_limit) { // sp outside stack
++ lo = hi + stack_limit;
++ }
++ #endif
+ }
+ GC_push_all_stack_sections(lo, hi, traced_stack_sect);
+ # ifdef STACK_GROWS_UP
diff --git a/flake.nix b/flake.nix
index 6c65e3406..8e7dd75d3 100644
--- a/flake.nix
+++ b/flake.nix
@@ -102,7 +102,13 @@
});
propagatedDeps =
- [ (boehmgc.override { enableLargeConfig = true; })
+ [ ((boehmgc.override {
+ enableLargeConfig = true;
+ }).overrideAttrs(o: {
+ patches = (o.patches or []) ++ [
+ ./boehmgc-coroutine-sp-fallback.diff
+ ];
+ }))
];
perlDeps =
--
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