master: Remove a hack from src/code/signal

The branch "master" has been updated in SBCL:
       via  526c5fca64c6346c89b574b5cb9d714ca6f77f56 (commit)
      from  aab1a9d230c5ed1cd09477e6176790a1b8f54053 (commit)

- Log -----------------------------------------------------------------
commit 526c5fca64c6346c89b574b5cb9d714ca6f77f56
Author: Douglas Katzman <[email protected]>
Date:   Thu Apr 9 13:31:42 2026 -0400

    Remove a hack from src/code/signal
    
    We should not set the (INFO :variable :always-bound symbol) property through
    ad-hoc techniques. The code and comments pre-date other approaches such as
    DEFINE-THREAD-LOCAL. However, that's actually not enough to get
    *UNBLOCK-DEFERRABLES-ON-ENABLING-INTERRUPTS-P* to work, because in addition to
    the issue cited at the call to INIT-MAIN-THREAD in src/code/cold-init, there
    is a problem that always-thread-local specials initialized from Lisp are set
    later than the ones intialized in alloc_thread_struct. So entirely-from-lisp
    assignment wasn't enough for *UNBLOCK-DEFERRABLES-ON-ENABLING-INTERRUPTS-P*.
---
 src/code/cold-init.lisp         |  9 +++++++--
 src/code/signal.lisp            | 15 ++-------------
 src/compiler/generic/parms.lisp |  5 +++++
 3 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/src/code/cold-init.lisp b/src/code/cold-init.lisp
index 387ef62eb..61c5f500f 100644
--- a/src/code/cold-init.lisp
+++ b/src/code/cold-init.lisp
@@ -136,7 +136,6 @@
           *trace-output* stream))
   (show-and-call !signal-function-cold-init)
   (show-and-call !printer-control-init) ; needed before first instance of FORMAT or WRITE-STRING
-  (setq sb-unix::*unblock-deferrables-on-enabling-interrupts-p* nil) ; needed by LOAD-LAYOUT called by CLASSES-INIT
   (setq *print-length* 6
         *print-level* 3)
   (/show "testing '/SHOW" *print-length* *print-level*) ; show anything
@@ -159,7 +158,13 @@
   (show-and-call !function-names-init)
   (show-and-call !pathname-cold-init)
 
-  ;; And now *CURRENT-THREAD*
+  ;; There is a very subtle (and slightly undiscoverable) chicken-and-egg situation
+  ;; which could occur when calling INIT-MAIN-THREAD during cold-init but presumably
+  ;; not after the core is produced: anything in *THREAD-LOCAL-SPECIALS* must
+  ;; have its initialization form evaluable.  This is surely fine for constants
+  ;; but not as clear for *HANDLER-CLUSTERS* which takes its value from
+  ;; **INITIAL-HANDLER-CLUSTERS**. As it happens, we're ok, but that's just one
+  ;; example, so sometimes you have to be careful with DEFINE-THREAD-LOCAL.
   (sb-thread::init-main-thread)
 
   (show-and-call !hash-table-cold-init)
diff --git a/src/code/signal.lisp b/src/code/signal.lisp
index 724a49772..af4ee038f 100644
--- a/src/code/signal.lisp
+++ b/src/code/signal.lisp
@@ -65,19 +65,8 @@
 ;;; would not cut it, as upon leaving WITHOUT-INTERRUPTS the pending
 ;;; handlers is run with stuff from the function in which this is
 ;;; still on the stack.
-(defvar *unblock-deferrables-on-enabling-interrupts-p* nil)
-
-(eval-when (:compile-toplevel :load-toplevel :execute)
-  (dolist (symbol '(*unblock-deferrables-on-enabling-interrupts-p*
-                    *interrupts-enabled*
-                    *interrupt-pending*
-                    #+sb-safepoint *thruption-pending*
-                    *allow-with-interrupts*))
-    ;; Force these to be always bound despite absence of a compile-time binding.
-    ;; (Avoid accidentally installing a value into symbol->value in cold-load)
-    ;; Not only are they always bound, 4 of them always have a thread-local value.
-    ;; We don't as yet have a way to elide the check for no-tls-value though.
-    (setf (info :variable :always-bound symbol) :always-bound)))
+;;; This is defined as a per-thread-c-interface symbol though C never reads it.
+(defvar *unblock-deferrables-on-enabling-interrupts-p*)
 
 (defmacro without-interrupts (&body body)
   "Executes BODY with all deferrable interrupts disabled. Deferrable
diff --git a/src/compiler/generic/parms.lisp b/src/compiler/generic/parms.lisp
index 782c483cf..bed4dacb9 100644
--- a/src/compiler/generic/parms.lisp
+++ b/src/compiler/generic/parms.lisp
@@ -179,10 +179,15 @@
 ;;;  - static for efficiency of access but need not be
 ;;; On #+sb-thread builds, these are not static, because access to them
 ;;; is via the TLS, not the symbol.
+;;; The default for all these is NIL if unspecified.
 (defconstant-eqx per-thread-c-interface-symbols
     (hash-cons
      '((*free-interrupt-context-index* 0)
        (sb-sys:*allow-with-interrupts* t)
+       ;; Being closely related to *INTERRUPTS-ENABLED*, the unblock-mumble var feels
+       ;; right at home here, though is not read from C. The reason it's needed here is
+       ;; that START-LISP uses WITHOUT-INTERRUPTS before INIT-THREAD-LOCAL-STORAGE.
+       sb-unix::*unblock-deferrables-on-enabling-interrupts-p*
        (sb-sys:*interrupts-enabled* t)
        sb-sys:*interrupt-pending*
        #+sb-safepoint sb-sys:*thruption-pending*

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