--- /dev/null
+From 632563b19ca72ec0ae10c7ed767a025c342d3155 Mon Sep 17 00:00:00 2001
+From: Xavier Leroy <xavier.leroy@college-de-france.fr>
+Date: Tue, 2 Mar 2021 19:06:56 +0100
+Subject: [PATCH 1/3] Dynamically allocate the alternate signal stack
+
+In Glibc 2.34 and later, SIGSTKSZ may not be a compile-time constant.
+It is no longer possible to statically allocate the alternate signal
+stack for the main thread, as we've been doing for the last 25 years.
+
+This commit implements dynamic allocation of the alternate signal stack
+even for the main thread. It reuses the code already in place to allocate
+the alternate signal stack for other threads.
+
+Fixes: #10250.
+---
+ runtime/caml/signals.h | 2 +-
+ runtime/signals_byt.c | 2 +-
+ runtime/signals_nat.c | 25 ++++++++++++++-----------
+ 3 files changed, 16 insertions(+), 13 deletions(-)
+
+diff --git a/runtime/caml/signals.h b/runtime/caml/signals.h
+index 3ff152c2693..285dbd7febd 100644
+--- a/runtime/caml/signals.h
++++ b/runtime/caml/signals.h
+@@ -87,7 +87,7 @@ value caml_do_pending_actions_exn (void);
+ value caml_process_pending_actions_with_root (value extra_root); // raises
+ value caml_process_pending_actions_with_root_exn (value extra_root);
+ int caml_set_signal_action(int signo, int action);
+-CAMLextern void caml_setup_stack_overflow_detection(void);
++CAMLextern int caml_setup_stack_overflow_detection(void);
+
+ CAMLextern void (*caml_enter_blocking_section_hook)(void);
+ CAMLextern void (*caml_leave_blocking_section_hook)(void);
+diff --git a/runtime/signals_byt.c b/runtime/signals_byt.c
+index 2183142da18..38eb5e3a47a 100644
+--- a/runtime/signals_byt.c
++++ b/runtime/signals_byt.c
+@@ -81,4 +81,4 @@ int caml_set_signal_action(int signo, int action)
+ return 0;
+ }
+
+-CAMLexport void caml_setup_stack_overflow_detection(void) {}
++CAMLexport int caml_setup_stack_overflow_detection(void) { return 0; }
+diff --git a/runtime/signals_nat.c b/runtime/signals_nat.c
+index 1be1b45d420..47b3e29af70 100644
+--- a/runtime/signals_nat.c
++++ b/runtime/signals_nat.c
+@@ -174,8 +174,6 @@ DECLARE_SIGNAL_HANDLER(trap_handler)
+ #error "CONTEXT_SP is required if HAS_STACK_OVERFLOW_DETECTION is defined"
+ #endif
+
+-static char sig_alt_stack[SIGSTKSZ];
+-
+ /* Code compiled with ocamlopt never accesses more than
+ EXTRA_STACK bytes below the stack pointer. */
+ #define EXTRA_STACK 256
+@@ -269,28 +267,33 @@ void caml_init_signals(void)
+ #endif
+
+ #ifdef HAS_STACK_OVERFLOW_DETECTION
+- {
+- stack_t stk;
++ if (caml_setup_stack_overflow_detection() != -1) {
+ struct sigaction act;
+- stk.ss_sp = sig_alt_stack;
+- stk.ss_size = SIGSTKSZ;
+- stk.ss_flags = 0;
+ SET_SIGACT(act, segv_handler);
+ act.sa_flags |= SA_ONSTACK | SA_NODEFER;
+ sigemptyset(&act.sa_mask);
+- if (sigaltstack(&stk, NULL) == 0) { sigaction(SIGSEGV, &act, NULL); }
++ sigaction(SIGSEGV, &act, NULL);
+ }
+ #endif
+ }
+
+-CAMLexport void caml_setup_stack_overflow_detection(void)
++/* Allocate and select an alternate stack for handling signals,
++ especially SIGSEGV signals.
++ Each thread needs its own alternate stack.
++ The alternate stack used to be statically-allocated for the main thread,
++ but this is incompatible with Glibc 2.34 and never, where SIGSTKSZ
++ may not be a compile-time constant (issue #10250). */
++
++CAMLexport int caml_setup_stack_overflow_detection(void)
+ {
+ #ifdef HAS_STACK_OVERFLOW_DETECTION
+ stack_t stk;
+ stk.ss_sp = malloc(SIGSTKSZ);
++ if (stk.ss_sp == NULL) return -1;
+ stk.ss_size = SIGSTKSZ;
+ stk.ss_flags = 0;
+- if (stk.ss_sp)
+- sigaltstack(&stk, NULL);
++ return sigaltstack(&stk, NULL);
++#else
++ return 0;
+ #endif
+ }
+
+From 9f5b312d457490032e21d54baa85774e78dcd6c9 Mon Sep 17 00:00:00 2001
+From: Xavier Leroy <xavier.leroy@college-de-france.fr>
+Date: Wed, 3 Mar 2021 17:57:25 +0100
+Subject: [PATCH 2/3] Typo in comment
+
+---
+ runtime/signals_nat.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/runtime/signals_nat.c b/runtime/signals_nat.c
+index 47b3e29af70..ca86956783c 100644
+--- a/runtime/signals_nat.c
++++ b/runtime/signals_nat.c
+@@ -281,7 +281,7 @@ void caml_init_signals(void)
+ especially SIGSEGV signals.
+ Each thread needs its own alternate stack.
+ The alternate stack used to be statically-allocated for the main thread,
+- but this is incompatible with Glibc 2.34 and never, where SIGSTKSZ
++ but this is incompatible with Glibc 2.34 and newer, where SIGSTKSZ
+ may not be a compile-time constant (issue #10250). */
+
+ CAMLexport int caml_setup_stack_overflow_detection(void)
+
+From 1a6cc6022e35b5a5e8e3b97586e78b39d78df51a Mon Sep 17 00:00:00 2001
+From: Xavier Leroy <xavier.leroy@college-de-france.fr>
+Date: Fri, 5 Mar 2021 19:10:11 +0100
+Subject: [PATCH 3/3] Update Changes
+
+---
+ Changes | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/Changes b/Changes
+index 1bb07e81d09..9c73ad02e32 100644
+--- a/Changes
++++ b/Changes
+@@ -69,6 +69,11 @@ Working version
+ to the debugger via a socket.
+ (Antonin Décimo, review by Xavier Leroy)
+
++- #10250, #10266: Dynamically allocate alternate signal stacks to
++ accommodate changes in Glibc 2.34.
++ (Xavier Leroy, reports by Tomasz Kłoczko and R.W.M. Jones, review by Anil
++ Madhavapeddy, Stephen Dolan, and Florian Angeletti)
++
+ ### Code generation and optimizations:
+
+ - #9876: do not cache the young_limit GC variable in a processor register.
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