Do not use assembly in GC_get_procedure_stack (E2K)

(a cherry-pick of commits d3f5bdc, 41d41c3 from 'master')

Issue #411 (bdwgc).

Use E2K_GET_PROCEDURE_STACK_SIZE and E2K_READ_PROCEDURE_STACK_EX
sub-functions (of access_hw_stacks syscall) instead of the legacy
E2K_READ_PROCEDURE_STACK one which required computation of ps_index
manually.  Check the stack size right before reading the stack (to
avoid EINVAL).

* mach_dep.c [E2K] (VA_SIZE, E2K_PSHTP_SIZE, VLIW_CMD_BRACES_PREFIX,
get_stack_index): Remove macro.
* mach_dep.c [E2K] (GC_get_procedure_stack): Initialize new_sz only
if buf is null; define stack_ofs local variable instead of ps; add
assertion that new_sz is non-zero and multiple of word size; use
E2K_GET_PROCEDURE_STACK_SIZE sub-function instead of
E2K_READ_PROCEDURE_STACK to get H/W procedure stack size (call
E2K_GET_PROCEDURE_STACK_SIZE sub-function right before
E2K_READ_PROCEDURE_STACK_EX one to check that the procedure stack size
has not changed since the previous call of
GC_get_procedure_stack(NULL,0)); do not use get_stack_index(); use
E2K_READ_PROCEDURE_STACK_EX sub-function (with stack_ofs=0) instead of
E2K_READ_PROCEDURE_STACK to read H/W procedure stack from the given
stack_ofs; print new_sz (in addition to errno) in case of error and
not EAGAIN; add comment.
* mach_dep.c [E2K && LOG_E2K_ALLOCS] (GC_get_procedure_stack): Remove
code.
* mach_dep.c [E2K && THREADS] (GC_alloc_and_get_procedure_stack): Add
TODO item.

mach_dep.c

@@ -32,69 +32,33 @@
 # include <sys/mman.h>
 # include <sys/syscall.h>
 
-# define VA_SIZE 48
-# define E2K_PSHTP_SIZE 12
-
-# if defined(__clang__)
-#   define VLIW_CMD_BRACES_PREFIX "%" /* a workaround for clang-9 */
-# else
-#   define VLIW_CMD_BRACES_PREFIX /* empty */
-# endif
-
-# define get_stack_index(ps_ptr)                    \
-        do {                                        \
-          word psp_lo, psp_hi;                      \
-          signed_word pshtp;                        \
-          char tmp = 0, val;                        \
-                                                    \
-          __asm__ __volatile__ (                    \
-            "1:\n\t"                                \
-            "ldb %4, 0, %0, mas = 7\n\t"            \
-            "rrd %%pshtp,  %1\n\t"                  \
-            "rrd %%psp.lo, %2\n\t"                  \
-            "rrd %%psp.hi, %3\n\t"                  \
-            VLIW_CMD_BRACES_PREFIX "{\n\t"          \
-            "  stb %4, 0, %0, mas = 2\n\t"          \
-            "  rbranch 1b\n\t"                      \
-            VLIW_CMD_BRACES_PREFIX "}"              \
-            : "=&r" (val), "=&r" (pshtp),           \
-              "=&r" (psp_lo), "=&r" (psp_hi)        \
-            : "r" (&tmp));                          \
-          *(ps_ptr) = (psp_lo & ((1UL<<VA_SIZE)-1)) \
-            + (unsigned)psp_hi                      \
-            + (word)((pshtp << (64-E2K_PSHTP_SIZE)) \
-                     >> (63-E2K_PSHTP_SIZE));       \
-        } while (0)
-
   GC_INNER size_t GC_get_procedure_stack(ptr_t buf, size_t buf_sz) {
-    word ps;
-    word new_sz = 0;
+    word new_sz;
 
     GC_ASSERT(0 == buf_sz || buf != NULL);
     for (;;) {
-      get_stack_index(&ps);
-      if (syscall(__NR_access_hw_stacks, E2K_READ_PROCEDURE_STACK,
-                  &ps, buf, buf_sz, &new_sz) != -1)
-        break;
-
-      if (ENOMEM == errno && (word)buf_sz < new_sz) {
-#       ifdef LOG_E2K_ALLOCS
-          if (buf_sz > 0) /* probably may happen */
-            GC_log_printf("GC_get_procedure_stack():"
-                          " buffer size/requested %lu/%lu bytes, GC #%lu\n",
-                          (unsigned long)buf_sz, (unsigned long)new_sz,
-                          (unsigned long)GC_gc_no);
-#       endif
-        return (size_t)new_sz; /* buffer not enough */
-      } else if (errno != EAGAIN) {
-        ABORT_ARG1("Cannot read procedure stack", ": errno= %d", errno);
+      word stack_ofs;
+
+      new_sz = 0;
+      if (syscall(__NR_access_hw_stacks, E2K_GET_PROCEDURE_STACK_SIZE,
+                  NULL, NULL, 0, &new_sz) == -1) {
+        if (errno != EAGAIN)
+          ABORT_ARG1("Cannot get size of procedure stack",
+                     ": errno= %d", errno);
+        continue;
       }
+      GC_ASSERT(new_sz > 0 && new_sz % sizeof(word) == 0);
+      if (new_sz > buf_sz)
+        break;
+      /* Immediately read the stack right after checking its size. */
+      stack_ofs = 0;
+      if (syscall(__NR_access_hw_stacks, E2K_READ_PROCEDURE_STACK_EX,
+                  &stack_ofs, buf, new_sz, NULL) != -1)
+        break;
+      if (errno != EAGAIN)
+        ABORT_ARG2("Cannot read procedure stack",
+                   ": new_sz= %lu, errno= %d", (unsigned long)new_sz, errno);
     }
-
-    if ((word)buf_sz < new_sz)
-      ABORT_ARG2("Buffer overflow while reading procedure stack",
-                 ": buf_sz= %lu, new_sz= %lu",
-                 (unsigned long)buf_sz, (unsigned long)new_sz);
     return (size_t)new_sz;
   }
 
@@ -124,6 +88,7 @@
 # ifdef THREADS
     GC_INNER size_t GC_alloc_and_get_procedure_stack(ptr_t *pbuf)
     {
+      /* TODO: support saving from non-zero ofs in stack */
       ptr_t buf = NULL;
       size_t new_sz, buf_sz;
 
@@ -142,9 +107,6 @@
       return new_sz;
     }
 # endif /* THREADS */
-
-# undef VLIW_CMD_BRACES_PREFIX
-# undef get_stack_index
 #endif /* E2K */
 
 #if defined(MACOS) && defined(__MWERKS__)