CLEANUP: rename O_C_STACK_GUARDED to O_ALTSIGSTACK

Nothing is guarded since the setjmp() context was removed; what the flag
enables is handling SIGSEGV on an alternative signal stack.  Also renames
initGuardCStack() to initAltSignalStack().

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017dv8qG8JrSfiHguZaFbLAW

Author: JanWielemaker

src/os/pl-cstack.c

@@ -411,7 +411,7 @@ bstore_print_backtrace_named(btrace *bt, const char *why)
 void
 initBackTrace(void)
 {
-#if defined(SIGSEGV) && !defined(O_C_STACK_GUARDED)
+#if defined(SIGSEGV) && !defined(O_ALTSIGSTACK)
   PL_signal(SIGSEGV, sigCrashHandler);
 #endif
 #ifdef SIGILL

src/pl-global.h

@@ -516,7 +516,7 @@ struct PL_local_data
 #ifndef __unix__
     int		forced;			/* Forced signal */
 #endif
-#ifdef O_C_STACK_GUARDED
+#ifdef O_ALTSIGSTACK
     void       *alt_stack;		/* Stack to handle SIGSEGV on */
 #endif
   } signal;

src/pl-incl.h

@@ -2357,7 +2357,7 @@ typedef sigmask_t		wsigmask_t[SIGMASK_WORDS];
 Report C-stack overflows. An overflow  raises SIGSEGV, but there is no C
 stack left to run the handler  on. On   POSIX  systems we therefore run
 SIGSEGV on an alternative signal stack,  so   that  sigCrashHandler() can
-still print the crash report. See initGuardCStack().
+still print the crash report. See initAltSignalStack().
 
 Code that may need more C stack than  is available asks for room using
 require_c_stack(), which raises resource_error(c_stack).
@@ -2368,7 +2368,7 @@ this when compiling with the address sanitizer.
 
 #if O_SIGNALS && defined(HAVE_SIGALTSTACK) && \
     !defined(__SANITIZE_ADDRESS__)
-#define O_C_STACK_GUARDED 1
+#define O_ALTSIGSTACK 1
 #endif
 
 

src/pl-setup.c

@@ -774,13 +774,13 @@ initTerminationSignals(void)
 #endif /*O_SIGNALS*/
 
 /* Handle SIGSEGV on an alternative signal stack, so a C-stack overflow
-   still gets us a crash report.  See O_C_STACK_GUARDED.
+   still gets us a crash report.  See O_ALTSIGSTACK.
 */
 
 bool
-initGuardCStack(void)
+initAltSignalStack(void)
 {
-#ifdef O_C_STACK_GUARDED
+#ifdef O_ALTSIGSTACK
   GET_LD
   stack_t ss = {0};
 
@@ -893,7 +893,7 @@ initSignals(DECL_LD)
   { struct signame *sn = signames;
 #ifdef HAVE_OS_SIGNALS
     initTerminationSignals();
-    initGuardCStack();
+    initAltSignalStack();
 #endif /*HAVE_OS_SIGNALS*/
     initBackTrace();
     for( ; sn->name; sn++)
@@ -1782,7 +1782,7 @@ freePrologLocalData(PL_local_data_t *ld)
   if ( ld->tabling.node_pool )
     free_alloc_pool(ld->tabling.node_pool);
 
-#ifdef O_C_STACK_GUARDED
+#ifdef O_ALTSIGSTACK
   if ( ld->signal.alt_stack )
     free(ld->signal.alt_stack);
 #endif

src/pl-setup.h

@@ -69,7 +69,7 @@ void		resetSignals(void);
 void		cleanupSignals(void);
 int		handleSignals(void);
 void		terminate_on_signal(int signo);
-bool		initGuardCStack(void);
+bool		initAltSignalStack(void);
 
 bool		initPrologStacks(size_t limit);
 void		initPrologLocalData(void);

src/pl-thread.c

@@ -656,7 +656,7 @@ initialise_thread(PL_thread_info_t *info)
   WITH_LD(info->thread_data) initPrologLocalData();
   info->thread_data->magic = LD_MAGIC;
 
-  initGuardCStack();
+  initAltSignalStack();
 
   return true;
 }