/dev/mem

kernel_module/user/README.md

@@ -8,5 +8,12 @@ C programs require cross compiling, but give us more control over system calls.
 
 These programs can also be compiled and used on host.
 
-1. [myinsmod](myinsmod.c)
-1. [myrmmod](myrmmod.c)
+1.  Standalone
+    1.  [myinsmod](myinsmod.c)
+    1.  [myrmmod](myrmmod.c)
+    1.  [devmem](devmem.c)
+    1.  [init_hello](init_hello.c)
+1.  Module tests
+    1.  [anonymous_inode](anonymous_inode.c)
+    1.  [poll](poll.c)
+    1.  [ioctl](ioctl.c)

kernel_module/user/devmem.c

@@ -0,0 +1,47 @@
+/*
+https://stackoverflow.com/questions/12040303/accessing-physical-address-from-user-space
+
+Sample call:
+
+	/phys.out 0 16
+
+Confirm memory from QEMU monitor with:
+
+	xp/0 16
+*/
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[]) {
+    if (argc < 3) {
+        printf("Usage: %s <phys_addr> <len>\n", argv[0]);
+        return 0;
+    }
+    off_t offset = strtoul(argv[1], NULL, 0);
+    size_t len = strtoul(argv[2], NULL, 0);
+
+    size_t pagesize = sysconf(_SC_PAGE_SIZE);
+    off_t page_base = (offset / pagesize) * pagesize;
+    off_t page_offset = offset - page_base;
+    int fd = open("/dev/mem", O_SYNC);
+	size_t reallen = page_offset + len;
+    unsigned char *mem = mmap(NULL, reallen, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, page_base);
+    if (mem == MAP_FAILED) {
+        perror("mmap");
+		exit(EXIT_FAILURE);
+    }
+    for (size_t i = 0; i < len; ++i) {
+        printf("%02x ", (unsigned int)mem[page_offset + i]);
+		mem[page_offset + i] = i % 256;
+	}
+	puts("");
+	if (munmap(mem, reallen) == -1) {
+		perror("munmap");
+		exit(EXIT_FAILURE);
+	}
+    return EXIT_SUCCESS;
+}