From 46b69073465f58847676d46ffcbdc93a0a46ce08 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Thalheim?= <joerg@thalheim.io>
Date: Mon, 11 Aug 2025 19:18:04 +0200
Subject: [PATCH] Revert "Merge pull request #13709 from
 NixOS/boehm-coroutines-sp"

This reverts commit 4b3ca9bd802f3cbdffb743cc399bad0af2ebfcf5, reversing
changes made to 867b69f53324226c35455471f3b10f2ffd12e67c.

Since this commit we get reproducible segfaults building Nix ci in macos github runners:
https://github.com/NixOS/nix/actions/runs/16885882321/job/47837390248
---
 src/libexpr/eval-gc.cc | 64 ------------------------------------------
 1 file changed, 64 deletions(-)

diff --git a/src/libexpr/eval-gc.cc b/src/libexpr/eval-gc.cc
index 9c050dc92..b17336a90 100644
--- a/src/libexpr/eval-gc.cc
+++ b/src/libexpr/eval-gc.cc
@@ -33,67 +33,6 @@ static void * oomHandler(size_t requested)
     throw std::bad_alloc();
 }
 
-/**
- * When a thread goes into a coroutine, we lose its original sp until
- * control flow returns to the thread. This causes Boehm GC to crash
- * since it will scan memory between the coroutine's sp and the
- * original stack base of the thread. Therefore, we detect when the
- * current sp is outside of the original thread stack and push the
- * entire thread stack instead, as an approximation.
- *
- * This is not optimal, because it causes the stack below sp to be
- * scanned. However, we usually we don't have active coroutines during
- * evaluation, so this is acceptable.
- *
- * Note that we don't scan coroutine stacks. It's currently assumed
- * that we don't have GC roots in coroutines.
- */
-void fixupBoehmStackPointer(void ** sp_ptr, void * _pthread_id)
-{
-    void *& sp = *sp_ptr;
-    auto pthread_id = reinterpret_cast<pthread_t>(_pthread_id);
-    size_t osStackSize;
-    // The low address of the stack, which grows down.
-    void * osStackLimit;
-
-#  ifdef __APPLE__
-    osStackSize = pthread_get_stacksize_np(pthread_id);
-    osStackLimit = pthread_get_stackaddr_np(pthread_id);
-#  else
-    pthread_attr_t pattr;
-    if (pthread_attr_init(&pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
-    }
-#    ifdef HAVE_PTHREAD_GETATTR_NP
-    if (pthread_getattr_np(pthread_id, &pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_getattr_np failed");
-    }
-#    elif HAVE_PTHREAD_ATTR_GET_NP
-    if (!pthread_attr_init(&pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_init failed");
-    }
-    if (!pthread_attr_get_np(pthread_id, &pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_get_np failed");
-    }
-#    else
-#      error "Need one of `pthread_attr_get_np` or `pthread_getattr_np`"
-#    endif
-    if (pthread_attr_getstack(&pattr, &osStackLimit, &osStackSize)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_getstack failed");
-    }
-    if (pthread_attr_destroy(&pattr)) {
-        throw Error("fixupBoehmStackPointer: pthread_attr_destroy failed");
-    }
-#  endif
-
-    void * osStackBase = (char *) osStackLimit + osStackSize;
-    // NOTE: We assume the stack grows down, as it does on all architectures we support.
-    //       Architectures that grow the stack up are rare.
-    if (sp >= osStackBase || sp < osStackLimit) { // sp is outside the os stack
-        sp = osStackLimit;
-    }
-}
-
 static inline void initGCReal()
 {
     /* Initialise the Boehm garbage collector. */
@@ -124,9 +63,6 @@ static inline void initGCReal()
 
     GC_set_oom_fn(oomHandler);
 
-    GC_set_sp_corrector(&fixupBoehmStackPointer);
-    assert(GC_get_sp_corrector());
-
     /* Set the initial heap size to something fairly big (25% of
        physical RAM, up to a maximum of 384 MiB) so that in most cases
        we don't need to garbage collect at all.  (Collection has a