Provide correct GC_uintptr_t, CPP_PTRSZ, GC_GRANULE_PTRS for CHERI

(a cherry-pick of commits 8120c8b, 4f431ac partly from capablevms/bdwgc)

Issue #627 (bdwgc).

Changes specific to CHERI capability systems are conditionally compiled
using the macro __CHERI_PURE_CAPABILITY__.

* include/gc/gc.h [_UINTPTR_T_DECLARED && !__MSYS__] (GC_uintptr_t):
Define to uintptr_t.
* include/gc/gc.h [__GNUC__ && !__INTEL_COMPILER
&& __CHERI_PURE_CAPABILITY__] (GC_reachable_here): Use "g" constraint
instead of "X".
* include/gc/gc_config_macros.h [__GNUC__
&& __CHERI_PURE_CAPABILITY__]: Include stdint.h; reformat comment.
* include/gc/gc_tiny_fl.h [!GC_GRANULE_BYTES
&& __CHERI_PURE_CAPABILITY__] (GC_GRANULE_PTRS): Define to 1 (instead
of 2).
* include/private/gcconfig.h [__CHERI_PURE_CAPABILITY__ && USE_MMAP]
(USE_MUNMAP): Undefine; add TODO item.
* include/private/gcconfig.h [!CPP_PTRSZ && __CHERI_PURE_CAPABILITY__]
(CPP_PTRSZ): Define to __SIZEOF_POINTER__*8 instead of CPP_WORDSZ.

Co-authored-by: Ivan Maidanski <[email protected]>

include/gc/gc.h

@@ -58,8 +58,10 @@ typedef GC_SIGNEDWORD GC_signed_word;
 #undef GC_SIGNEDWORD
 #undef GC_UNSIGNEDWORD
 
-#if (defined(_UINTPTR_T) || defined(_UINTPTR_T_DEFINED)) && !defined(__MSYS__)
-/* Note: MSYS2 might provide __uintptr_t instead of uintptr_t.  */
+#if (defined(_UINTPTR_T) || defined(_UINTPTR_T_DECLARED) \
+     || defined(_UINTPTR_T_DEFINED))                     \
+    && !defined(__MSYS__)
+/* Note: MSYS2 might provide __uintptr_t but not uintptr_t. */
 typedef uintptr_t GC_uintptr_t;
 #else
 typedef GC_word GC_uintptr_t;
@@ -1476,7 +1478,7 @@ GC_API int GC_CALL GC_invoke_finalizers(void);
 #if defined(__GNUC__) && !defined(__INTEL_COMPILER) \
     && !(defined(__APPLE__) && defined(__arm__) && defined(__TINYC__))
 /* TCC (as of v0.9.28rc) does not support asm on macOS/arm. */
-#  if defined(__TINYC__)
+#  if defined(__CHERI_PURE_CAPABILITY__) || defined(__TINYC__)
 #    define GC_reachable_here(ptr) \
       __asm__ __volatile__(" " : : "g"(ptr) : "memory")
 #  elif defined(__e2k__)

include/gc/gc_config_macros.h

@@ -189,13 +189,13 @@
 #  define __GC
 #  if !defined(_WIN32_WCE) || defined(__GNUC__)
 #    include <stddef.h>
-#    if defined(__MINGW32__) && !defined(_WIN32_WCE)
+#    if defined(__MINGW32__) && !defined(_WIN32_WCE) \
+        || defined(__CHERI_PURE_CAPABILITY__)
 #      include <stdint.h>
-/* We mention uintptr_t.                                            */
-/* Perhaps this should be included in pure msft environments        */
-/* as well?                                                         */
+/* We mention uintptr_t.  Perhaps this should be included in pure   */
+/* msft environments as well.                                       */
 #    endif
-#  else                 /* _WIN32_WCE */
+#  else
 /* Yet more kludges for WinCE.        */
 #    include <stdlib.h> /* size_t is defined here */
 #    ifndef _PTRDIFF_T_DEFINED

include/gc/gc_tiny_fl.h

@@ -48,7 +48,11 @@
 #ifdef GC_GRANULE_BYTES
 #  define GC_GRANULE_PTRS (GC_GRANULE_BYTES / GC_SIZEOF_PTR)
 #else
-#  define GC_GRANULE_PTRS 2 /* in pointers */
+#  if defined(__CHERI_PURE_CAPABILITY__)
+#    define GC_GRANULE_PTRS 1
+#  else
+#    define GC_GRANULE_PTRS 2 /* in pointers */
+#  endif
 #  define GC_GRANULE_BYTES (GC_GRANULE_PTRS * GC_SIZEOF_PTR)
 #endif /* !GC_GRANULE_BYTES */
 

include/private/gcconfig.h

@@ -2488,6 +2488,11 @@ extern char __global_base, __heap_base;
 #  define USE_MMAP_ANON
 #endif
 
+#if defined(__CHERI_PURE_CAPABILITY__) && defined(USE_MMAP)
+/* TODO: currently turned off to avoid downgrading permissions on CHERI */
+#  undef USE_MUNMAP
+#endif
+
 #if defined(REDIRECT_MALLOC) && defined(THREADS) \
     && (defined(LINUX) || defined(NACL))
 /* TODO: Unclear if NaCl really needs this. */
@@ -2674,7 +2679,11 @@ EXTERN_C_BEGIN
 #endif
 
 #ifndef CPP_PTRSZ
-#  define CPP_PTRSZ CPP_WORDSZ
+#  if defined(__CHERI_PURE_CAPABILITY__)
+#    define CPP_PTRSZ (__SIZEOF_POINTER__ * 8)
+#  else
+#    define CPP_PTRSZ CPP_WORDSZ
+#  endif
 #endif
 
 #ifndef CPPCHECK