Remove unused JL_HAVE_SIGALTSTACK code

Nothing is ever activating this, and it probably hasn't been
tested in a while.

Author: fingolfin

src/gc-stacks.c

@@ -76,7 +76,7 @@ static void *malloc_stack(size_t bufsz) JL_NOTSAFEPOINT
     if (stk == MAP_FAILED)
         return MAP_FAILED;
 
-#if !defined(JL_HAVE_UCONTEXT) && !defined(JL_HAVE_SIGALTSTACK)
+#if !defined(JL_HAVE_UCONTEXT)
     // set up a guard page to detect stack overflow
     if (mprotect(stk, jl_guard_size, PROT_NONE) == -1) {
         munmap(stk, bufsz);

src/julia_threads.h

@@ -31,7 +31,6 @@ JL_DLLEXPORT int8_t jl_threadpoolid(int16_t tid) JL_NOTSAFEPOINT;
 // JL_HAVE_ASM && JL_HAVE_UNW_CONTEXT -- libunwind-based
 // JL_HAVE_UNW_CONTEXT -- libunwind-based
 // JL_HAVE_UCONTEXT -- posix standard API, requires syscall for resume
-// JL_HAVE_SIGALTSTACK -- requires several syscall for start, setjmp for resume
 
 #ifdef _OS_WINDOWS_
 #define JL_HAVE_UCONTEXT
@@ -53,8 +52,7 @@ typedef struct {
 } jl_stack_context_t;
 #if !defined(JL_HAVE_UCONTEXT) && \
     !defined(JL_HAVE_ASM) && \
-    !defined(JL_HAVE_UNW_CONTEXT) && \
-    !defined(JL_HAVE_SIGALTSTACK)
+    !defined(JL_HAVE_UNW_CONTEXT)
 #if (defined(_CPU_X86_64_) || defined(_CPU_X86_) || defined(_CPU_AARCH64_) ||  \
      defined(_CPU_ARM_) || defined(_CPU_PPC64_))
 #define JL_HAVE_ASM
@@ -70,7 +68,7 @@ typedef struct {
 #endif
 #endif
 
-#if (!defined(JL_HAVE_UNW_CONTEXT) && defined(JL_HAVE_ASM)) || defined(JL_HAVE_SIGALTSTACK)
+#if !defined(JL_HAVE_UNW_CONTEXT) && defined(JL_HAVE_ASM)
 typedef jl_stack_context_t _jl_ucontext_t;
 #endif
 #pragma GCC visibility push(default)

src/stackwalk.c

@@ -1151,8 +1151,6 @@ static void jl_rec_backtrace(jl_task_t *t) JL_NOTSAFEPOINT
       #pragma message("jl_rec_backtrace not defined for ASM/SETJMP on unknown system")
       (void)c;
      #endif
-#elif defined(JL_HAVE_SIGALTSTACK)
-     #pragma message("jl_rec_backtrace not defined for SIGALTSTACK")
 #else
      #pragma message("jl_rec_backtrace not defined for unknown task system")
 #endif

src/task.c

@@ -272,7 +272,7 @@ JL_NO_ASAN static void restore_stack2(jl_task_t *t, jl_ptls_t ptls, jl_task_t *l
         return;
     if (r != 0 || returns != 1)
         abort();
-#elif defined(JL_HAVE_ASM) || defined(JL_HAVE_SIGALTSTACK) || defined(_OS_WINDOWS_)
+#elif defined(JL_HAVE_ASM) || defined(_OS_WINDOWS_)
     if (jl_setjmp(lastt->ctx.copy_ctx.uc_mcontext, 0))
         return;
 #else
@@ -1472,98 +1472,6 @@ JL_NO_ASAN static void jl_start_fiber_set(jl_ucontext_t *t)
 }
 #endif
 
-#if defined(JL_HAVE_SIGALTSTACK)
-#if defined(_COMPILER_TSAN_ENABLED_)
-#error TSAN support not currently implemented for this tasking model
-#endif
-
-static void start_basefiber(int sig)
-{
-    jl_ptls_t ptls = jl_current_task->ptls;
-    if (jl_setjmp(ptls->base_ctx.uc_mcontext, 0))
-        start_task(); // sanitizer_finish_switch_fiber is part of start_task
-}
-static char *jl_alloc_fiber(_jl_ucontext_t *t, size_t *ssize, jl_task_t *owner)
-{
-    stack_t uc_stack, osigstk;
-    struct sigaction sa, osa;
-    sigset_t set, oset;
-    void *stk = jl_malloc_stack(ssize, owner);
-    if (stk == NULL)
-        return NULL;
-    // setup
-    jl_ptls_t ptls = jl_current_task->ptls;
-    _jl_ucontext_t base_ctx;
-    memcpy(&base_ctx, &ptls->base_ctx, sizeof(base_ctx));
-    sigfillset(&set);
-    if (pthread_sigmask(SIG_BLOCK, &set, &oset) != 0) {
-       jl_free_stack(stk, *ssize);
-       jl_error("pthread_sigmask failed");
-    }
-    uc_stack.ss_sp = stk;
-    uc_stack.ss_size = *ssize;
-    uc_stack.ss_flags = 0;
-    if (sigaltstack(&uc_stack, &osigstk) != 0) {
-       jl_free_stack(stk, *ssize);
-       jl_error("sigaltstack failed");
-    }
-    memset(&sa, 0, sizeof(sa));
-    sigemptyset(&sa.sa_mask);
-    sa.sa_handler = start_basefiber;
-    sa.sa_flags = SA_ONSTACK;
-    if (sigaction(SIGUSR2, &sa, &osa) != 0) {
-       jl_free_stack(stk, *ssize);
-       jl_error("sigaction failed");
-    }
-    // emit signal
-    pthread_kill(pthread_self(), SIGUSR2); // initializes jl_basectx
-    sigdelset(&set, SIGUSR2);
-    sigsuspend(&set);
-    // cleanup
-    if (sigaction(SIGUSR2, &osa, NULL) != 0) {
-       jl_free_stack(stk, *ssize);
-       jl_error("sigaction failed");
-    }
-    if (osigstk.ss_size < MINSTKSZ && (osigstk.ss_flags | SS_DISABLE))
-       osigstk.ss_size = MINSTKSZ;
-    if (sigaltstack(&osigstk, NULL) != 0) {
-       jl_free_stack(stk, *ssize);
-       jl_error("sigaltstack failed");
-    }
-    if (pthread_sigmask(SIG_SETMASK, &oset, NULL) != 0) {
-       jl_free_stack(stk, *ssize);
-       jl_error("pthread_sigmask failed");
-    }
-    if (&ptls->base_ctx != t) {
-        memcpy(&t, &ptls->base_ctx, sizeof(base_ctx));
-        memcpy(&ptls->base_ctx, &base_ctx, sizeof(base_ctx)); // restore COPY_STACKS context
-    }
-    return (char*)stk;
-}
-static void jl_start_fiber_set(jl_ucontext_t *t) {
-    jl_longjmp(t->ctx.uc_mcontext, 1); // (doesn't return)
-}
-static void jl_start_fiber_swap(jl_ucontext_t *lastt, jl_ucontext_t *t)
-{
-    assert(lastt);
-    if (lastt && jl_setjmp(lastt->ctx.uc_mcontext, 0))
-        return;
-    tsan_switch_to_ctx(t);
-    jl_start_fiber_set(t);
-}
-static void jl_swap_fiber(jl_ucontext_t *lastt, jl_ucontext_t *t)
-{
-    if (jl_setjmp(lastt->ctx.uc_mcontext, 0))
-        return;
-    tsan_switch_to_ctx(t);
-    jl_start_fiber_set(t); // doesn't return
-}
-static void jl_set_fiber(jl_ucontext_t *t)
-{
-    jl_longjmp(t->ctx.uc_mcontext, 1);
-}
-#endif
-
 // Initialize a root task using the given stack.
 jl_task_t *jl_init_root_task(jl_ptls_t ptls, void *stack_lo, void *stack_hi)
 {