update cheri article

_posts/cheri/code/Makefile

@@ -1,5 +1,5 @@
 CFLAGS += -Wall -g -fno-stack-protector -O0
-CC ?= clang
+CC := clang
 PURECAP_CC ?= ~/cheri/output/sdk/utils/cheribsd-riscv64-purecap-clang
 
 SOURCES := $(wildcard *.c)

_posts/cheri/code/ptrtypes.c

@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <stdint.h>
+
+int main() {
+    printf("type          size (hex)   size (dec)\n");
+    printf("=====================================\n");
+#ifdef __PTRADDR_TYPE__
+    printf("ptraddr_t     0x%.2lx         %.2lu\n", sizeof(ptraddr_t), sizeof(ptraddr_t));
+#endif
+    printf("uintptr_t     0x%.2lx         %.2lu\n", sizeof(uintptr_t), sizeof(uintptr_t));
+    printf("size_t        0x%.2lx         %.2lu\n", sizeof(size_t), sizeof(size_t));
+    printf("void*         0x%.2lx         %.2lu\n", sizeof(void*), sizeof(void*));
+    printf("=====================================\n");
+
+#ifdef __CHERI__
+    int x = 111;
+    int y[] = { 888, 999 };
+
+    int *a = &x;
+    int *b = &(y[0]);
+
+    // transplant address from capability a to capability b
+    printf("*b: %d\n", *b);
+    ptraddr_t a_addr = __builtin_cheri_address_get(a);
+    b = __builtin_cheri_address_set(a, a_addr);
+    printf("*b: %d\n", *b);
+
+    b = &(y[0]);
+    // uintptr_t is an unsigned integer type that preserves capabilities
+    uintptr_t b_uintptr = (uintptr_t) b;
+    b_uintptr += sizeof(int);
+    b = (int*) b_uintptr;
+    printf("*b: %d\n", *b);
+#endif
+
+    return 0;
+}