Revert hack for musl libc

Decreasing the alien stack ptr by a word is expressly the wrong thing
because we want to catch, not hide, any mis-use of the stack.

So put in a diffent hack to detect structure size mismatch before
cold-init, and also have grovel-headers output a hardcoded definition
(for lack of a better idea) if the auto-defined struct would be wrong.

src/code/target-alieneval.lisp

@@ -860,3 +860,14 @@ way that the argument is passed.
 
 (defun alien-void-type-p (type)
   (and (alien-values-type-p type) (not (alien-values-type-values type))))
+
+;;; Assert that two important types aren't messed up
+(eval-when (:compile-toplevel)
+  (flet ((check-size (tag)
+           (let ((alien-type (parse-alien-type `(struct ,tag) nil)))
+             (unless (= (alien-type-bits alien-type)
+                        (* (symbol-value (package-symbolicate "SB-UNIX" "SIZEOF-" tag))
+                           sb-vm:n-byte-bits))
+               (error "(STRUCT ~S) has unexpected size" tag)))))
+    (check-size 'sb-unix::timespec)
+    (check-size 'sb-unix::timeval)))

src/runtime/thread.c

@@ -1041,7 +1041,13 @@ alloc_thread_struct(void* spaces) {
     th->state_word.user_thread_p = 1;
 
     lispobj* alien_stack_end = (lispobj*)((char*)th->alien_stack_start + ALIEN_STACK_SIZE);
+#if defined LISP_FEATURE_X86 || defined LISP_FEATURE_X86_64
+    // Alien-stack-pointer is predecremented upon use
+    th->alien_stack_pointer = alien_stack_end;
+#else
+    // I do not know the convention for alien-stack-pointer
     th->alien_stack_pointer = alien_stack_end - 1;
+#endif
 
 #ifdef HAVE_THREAD_PSEUDO_ATOMIC_BITS_SLOT
     memset(&th->pseudo_atomic_bits, 0, sizeof th->pseudo_atomic_bits);

tests/x86-linux.impure.lisp

@@ -1,16 +1,5 @@
 #+(or (not x86) (not linux)) (invoke-restart 'run-tests::skip-file)
 
-;;; I'm not entirely satisfied with the solution to fixing the crash on Alpine linux
-;;; and while investigating that, I found also that we supplied too high a limit
-;;; to set_thread_area().
-
-;;; [As to the problem on Alpine: if it were the case that we don't pre-decrement the
-;;; alien-stack-pointer then we'd surely clobber th->no_tls_value_marker.
-;;; But it works everywhere else. Alpine uses musl libc, so perhaps that's the distinguishing
-;;; feature - something in libc takes an alien we allocated and writes past it by a word
-;;; because we still after all these years don't fully get the structure padding requirements
-;;; in the 32-bit ABI correct.]
-
 (in-package sb-vm)
 
 (defconstant os-page-size 4096)

tools-for-build/grovel-headers.c

@@ -380,9 +380,25 @@ main(int argc, char __attribute__((unused)) *argv[])
     DEFSTRUCT(timeval, struct timeval,
         DEFSLOT(tv-sec, tv_sec);
         DEFSLOT(tv-usec, tv_usec));
+    // There is no way to detect musl libc (https://wiki.musl-libc.org/faq)
+    // I'm really just guessing, but maybe 32-bit ARM has padding too
+#if defined LISP_FEATURE_LINUX && defined LISP_FEATURE_LITTLE_ENDIAN \
+  && (defined LISP_FEATURE_X86 || defined LISP_FEATURE_ARM)
+    struct timespec dummy_ts;
+    if (sizeof dummy_ts > sizeof dummy_ts.tv_sec + sizeof dummy_ts.tv_nsec) {
+        fprintf(stderr, "WARNING: Assuming physical layout of timespec\n");
+        printf("(define-alien-type nil\n\
+  (struct timespec\n\
+          (tv-sec (signed 64))\n\
+          (tv-nsec (signed 32))\n\
+          (padding (signed 32))))\n");
+    } else
+#endif
     DEFSTRUCT(timespec, struct timespec,
         DEFSLOT(tv-sec, tv_sec);
         DEFSLOT(tv-nsec, tv_nsec));
+    defconstant("sizeof-timespec", sizeof (struct timespec));
+    defconstant("sizeof-timeval", sizeof (struct timeval));
     printf("\n");
 
 #ifdef LISP_FEATURE_ANDROID