diff --git a/toolbox/Android.mk b/toolbox/Android.mk
index 94029d8..c4795a7 100644
--- a/toolbox/Android.mk
+++ b/toolbox/Android.mk
@@ -59,3 +59,12 @@
 $(INPUT_H_LABELS_H): $(LOCAL_PATH)/Android.mk $(LOCAL_PATH)/generate-input.h-labels.py $(UAPI_INPUT_EVENT_CODES_H)
 $(INPUT_H_LABELS_H):
 	$(transform-generated-source)
+
+# We only want 'r' on userdebug and eng builds.
+include $(CLEAR_VARS)
+LOCAL_SRC_FILES := r.c
+LOCAL_CFLAGS += $(common_cflags)
+LOCAL_C_INCLUDES += $(LOCAL_PATH)/upstream-netbsd/include/
+LOCAL_MODULE := r
+LOCAL_MODULE_TAGS := debug
+include $(BUILD_EXECUTABLE)
diff --git a/toolbox/r.c b/toolbox/r.c
new file mode 100644
index 0000000..b96cdb2
--- /dev/null
+++ b/toolbox/r.c
@@ -0,0 +1,102 @@
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#if __LP64__
+#define strtoptr strtoull
+#else
+#define strtoptr strtoul
+#endif
+
+static int usage()
+{
+    fprintf(stderr,"r [-b|-s] <address> [<value>]\n");
+    return -1;
+}
+
+int main(int argc, char *argv[])
+{
+    if(argc < 2) return usage();
+
+    int width = 4;
+    if(!strcmp(argv[1], "-b")) {
+        width = 1;
+        argc--;
+        argv++;
+    } else if(!strcmp(argv[1], "-s")) {
+        width = 2;
+        argc--;
+        argv++;
+    }
+
+    if(argc < 2) return usage();
+    uintptr_t addr = strtoptr(argv[1], 0, 16);
+
+    uintptr_t endaddr = 0;
+    char* end = strchr(argv[1], '-');
+    if (end)
+        endaddr = strtoptr(end + 1, 0, 16);
+
+    if (!endaddr)
+        endaddr = addr + width - 1;
+
+    if (endaddr <= addr) {
+        fprintf(stderr, "end address <= start address\n");
+        return -1;
+    }
+
+    bool set = false;
+    uint32_t value = 0;
+    if(argc > 2) {
+        set = true;
+        value = strtoul(argv[2], 0, 16);
+    }
+
+    int fd = open("/dev/mem", O_RDWR | O_SYNC);
+    if(fd < 0) {
+        fprintf(stderr,"cannot open /dev/mem\n");
+        return -1;
+    }
+
+    off64_t mmap_start = addr & ~(PAGE_SIZE - 1);
+    size_t mmap_size = endaddr - mmap_start + 1;
+    mmap_size = (mmap_size + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1);
+
+    void* page = mmap64(0, mmap_size, PROT_READ | PROT_WRITE,
+                        MAP_SHARED, fd, mmap_start);
+
+    if(page == MAP_FAILED){
+        fprintf(stderr,"cannot mmap region\n");
+        return -1;
+    }
+
+    while (addr <= endaddr) {
+        switch(width){
+        case 4: {
+            uint32_t* x = (uint32_t*) (((uintptr_t) page) + (addr & 4095));
+            if(set) *x = value;
+            fprintf(stderr,"%08"PRIxPTR": %08x\n", addr, *x);
+            break;
+        }
+        case 2: {
+            uint16_t* x = (uint16_t*) (((uintptr_t) page) + (addr & 4095));
+            if(set) *x = value;
+            fprintf(stderr,"%08"PRIxPTR": %04x\n", addr, *x);
+            break;
+        }
+        case 1: {
+            uint8_t* x = (uint8_t*) (((uintptr_t) page) + (addr & 4095));
+            if(set) *x = value;
+            fprintf(stderr,"%08"PRIxPTR": %02x\n", addr, *x);
+            break;
+        }
+        }
+        addr += width;
+    }
+    return 0;
+}