From c6edbfddb078cc36cd0dfbabe79c1b54d6171cf1 Mon Sep 17 00:00:00 2001
From: Ciro Santilli <ciro.santilli@gmail.com>
Date: Sat, 5 Aug 2017 21:24:16 +0100
Subject: [PATCH] devmem3 cleanup further

---
 kernel_module/user/devmem3.c | 57 +++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 27 deletions(-)

diff --git a/kernel_module/user/devmem3.c b/kernel_module/user/devmem3.c
index eb1d8e5..2ffd914 100644
--- a/kernel_module/user/devmem3.c
+++ b/kernel_module/user/devmem3.c
@@ -1,33 +1,36 @@
 /*
 Adapted from: http://free-electrons.com/pub/mirror/devmem2.c
+
+Forked because of the unpredictable access widths:
+https://bugs.busybox.net/show_bug.cgi?id=10171
 */
 
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <unistd.h>
 #include <string.h>
-#include <errno.h>
-#include <signal.h>
-#include <fcntl.h>
-#include <ctype.h>
-#include <termios.h>
-#include <sys/types.h>
 #include <sys/mman.h>
-#include <stdint.h>
-  
+#include <sys/types.h>
+#include <termios.h>
+#include <unistd.h>
+
 #define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
   __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)
- 
-#define MAP_SIZE 4096UL
-#define MAP_MASK (MAP_SIZE - 1)
 
 int main(int argc, char **argv) {
-    int fd;
-    void *map_base, *virt_addr; 
-	uintmax_t read_result, writeval;
-	off_t target;
 	int access_type = 'w';
-	
+	unsigned long map_size, map_mask;
+	off_t target;
+	uintmax_t read_result, writeval;
+    int fd;
+    void *map_base, *virt_addr;
+
+    map_size = sysconf(_SC_PAGE_SIZE);
+    map_mask = map_size - 1;
 	if(argc < 2) {
 		fprintf(stderr, "\nUsage:\t%s { address } [ type [ data ] ]\n"
 			"\taddress : memory address to act upon\n"
@@ -43,16 +46,16 @@ int main(int argc, char **argv) {
 
 
     if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
-    printf("/dev/mem opened.\n"); 
+    printf("/dev/mem opened.\n");
     fflush(stdout);
-    
+
     /* Map one page */
-    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK);
+    map_base = mmap(0, map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~map_mask);
     if(map_base == (void *) -1) FATAL;
-    printf("Memory mapped at address %p.\n", map_base); 
+    printf("Memory mapped at address %p.\n", map_base);
     fflush(stdout);
-    
-    virt_addr = map_base + (target & MAP_MASK);
+
+    virt_addr = map_base + (target & map_mask);
     switch(access_type) {
 		case 'b':
 			read_result = *((uint8_t *) virt_addr);
@@ -70,7 +73,7 @@ int main(int argc, char **argv) {
 			fprintf(stderr, "Illegal data type '%c'.\n", access_type);
 			exit(2);
 	}
-    printf("Value at address 0x%jX (%p): 0x%jX\n", (uintmax_t)target, virt_addr, (uintmax_t)read_result); 
+    printf("Value at address 0x%jX (%p): 0x%jX\n", (uintmax_t)target, virt_addr, (uintmax_t)read_result);
     fflush(stdout);
 
 	if(argc > 3) {
@@ -93,11 +96,11 @@ int main(int argc, char **argv) {
 				read_result = *((uint64_t *) virt_addr);
 				break;
 		}
-		printf("Written 0x%X; readback 0x%jX\n", (unsigned int)writeval, (unsigned int)read_result); 
+		printf("Written 0x%jX; readback 0x%jX\n", (uintmax_t)writeval, (uintmax_t)read_result);
 		fflush(stdout);
 	}
-	
-	if(munmap(map_base, MAP_SIZE) == -1) FATAL;
+
+	if(munmap(map_base, map_size) == -1) FATAL;
     close(fd);
     return 0;
 }