Fix mmap() failure with EPROT on CHERI

Issue ivmai#627 (bdwgc).

It is essential for CHERI to have only address part in `last_addr`
without metadata (thus the variable is of `word` type intentionally),
otherwise `mmap()` fails setting `errno` to `EPROT`.

* dyn_load.c [DYNAMIC_LOADING && !ANY_MSWIN && (USE_PROC_FOR_LIBRARIES
&& !LINUX || IRIX5)] (GC_register_dynamic_libraries): Do not use
`ADDR()` for `HEAP_START`.
* include/private/gcconfig.h [SOLARIS && USE_MMAP || I386 && (DGUX
|| LINUX) || MIPS && IRIX5 && USE_MMAP] (HEAP_START): Cast to `word`
instead of use of `MAKE_CPTR()`.
* include/private/gcconfig.h [SOLARIS && !USE_MMAP  || MIPS && IRIX5
&& !USE_MMAP] (HEAP_START): Use `ADDR()`.
* include/private/gcconfig.h [!HEAP_START] (HEAP_START): Remove cast to
`ptr_t`.
* os_dep.c [NEED_UNIX_GET_MEM && MMAP_SUPPORTED && !MSWIN_XBOX1]
(GC_unix_mmap_get_mem): Change type of `last_addr` from `ptr_t` to
`word`; do not use `MAKE_CPTR()` for `last_addr`; add comment near
`last_addr` usage; reduce length of abort message; do not align
`(ptr_t)result+bytes` because `result` and `bytes` should be
page-aligned; update `last_addr` value after checking that `result` is
HBLKSIZE-aligned; add assertion that updated `last_addr` value is
page-aligned.

Author: ivmai

dyn_load.c

@@ -991,7 +991,7 @@ GC_register_dynamic_libraries(void)
   long flags;
   ptr_t start;
   ptr_t limit;
-  word heap_start = ADDR(HEAP_START);
+  word heap_start = HEAP_START;
   word heap_end = heap_start;
 #    ifdef SOLARISDL
 #      define MA_PHYS 0

include/private/gcconfig.h

@@ -1102,9 +1102,9 @@ extern int _end[];
 /* doesn't interact correctly with the system malloc.         */
 #  endif
 #  ifdef USE_MMAP
-#    define HEAP_START MAKE_CPTR(0x40000000)
+#    define HEAP_START ((word)0x40000000)
 #  else
-#    define HEAP_START DATAEND
+#    define HEAP_START ADDR(DATAEND)
 #  endif
 #  ifndef GC_THREADS
 #    define MPROTECT_VDB
@@ -1447,12 +1447,12 @@ extern int _etext, _end;
 #      define USE_MMAP 1
 #    endif
 #    define MAP_FAILED (void *)((GC_uintptr_t)-1)
-#    define HEAP_START MAKE_CPTR(0x40000000)
+#    define HEAP_START ((word)0x40000000)
 #  endif /* DGUX */
 #  ifdef LINUX
 /* This encourages mmap to give us low addresses,       */
 /* thus allowing the heap to grow to ~3 GB.             */
-#    define HEAP_START MAKE_CPTR(0x1000)
+#    define HEAP_START ((word)0x1000)
 #    ifdef __ELF__
 #      if GC_GLIBC_PREREQ(2, 0) || defined(HOST_ANDROID)
 #        define SEARCH_FOR_DATA_START
@@ -1718,9 +1718,9 @@ extern int _fdata[];
 /* there.  In either case it is used to identify heap sections so */
 /* they are not considered as roots.                              */
 #    ifdef USE_MMAP
-#      define HEAP_START MAKE_CPTR(0x30000000)
+#      define HEAP_START ((word)0x30000000)
 #    else
-#      define HEAP_START DATASTART
+#      define HEAP_START ADDR(DATASTART)
 #    endif
 /* MPROTECT_VDB should work, but there is evidence of a breakage. */
 #    define DYNAMIC_LOADING
@@ -2992,7 +2992,7 @@ extern ptr_t GC_data_start;
 #endif
 
 #ifndef HEAP_START
-#  define HEAP_START ((ptr_t)0)
+#  define HEAP_START 0
 #endif
 
 #ifndef CLEAR_DOUBLE

os_dep.c

@@ -2335,7 +2335,7 @@ STATIC void *
 GC_unix_mmap_get_mem(size_t bytes)
 {
   void *result;
-  static ptr_t last_addr = HEAP_START;
+  static word last_addr = HEAP_START;
 
 #      ifndef USE_MMAP_ANON
   static GC_bool initialized = FALSE;
@@ -2362,8 +2362,11 @@ GC_unix_mmap_get_mem(size_t bytes)
   GC_ASSERT(GC_page_size != 0);
   if (bytes & (GC_page_size - 1))
     ABORT("Bad GET_MEM arg");
+  /* Note: it is essential for CHERI to have only address part in   */
+  /* last_addr without metadata (thus the variable is of word type  */
+  /* intentionally), otherwise mmap() fails setting errno to EPROT. */
   result
-      = mmap(last_addr, bytes,
+      = mmap(MAKE_CPTR(last_addr), bytes,
              (PROT_READ | PROT_WRITE) | (GC_pages_executable ? PROT_EXEC : 0),
              GC_MMAP_FLAGS | OPT_MAP_ANON, zero_fd, 0 /* offset */);
 #      undef IGNORE_PAGES_EXECUTABLE
@@ -2387,11 +2390,10 @@ GC_unix_mmap_get_mem(size_t bytes)
     return GC_unix_mmap_get_mem(bytes);
   }
 #      endif
-  last_addr = PTR_ALIGN_UP((ptr_t)result + bytes, GC_page_size);
-
   if ((ADDR(result) % HBLKSIZE) != 0)
-    ABORT("GC_unix_get_mem: Memory returned by mmap is not aligned to "
-          "HBLKSIZE.");
+    ABORT("Memory returned by mmap is not aligned to HBLKSIZE");
+  last_addr = ADDR(result) + bytes;
+  GC_ASSERT((last_addr & (GC_page_size - 1)) == 0);
   return result;
 }
 #    endif /* !MSWIN_XBOX1 */