devmem: new command.

Intended to replace Android's toolbox `r`, but behaving more like a
drop-in replacement for busybox's `devmem`.

1 files changed, 62 insertions, 0 deletions

diff --git a/toys/pending/devmem.c b/toys/pending/devmem.c
new file mode 100644
index 00000000..d5b7bdb4
--- /dev/null
+++ b/toys/pending/devmem.c
@@ -0,0 +1,62 @@
+/* devmem.c - Access physical addresses
+ *
+ * Copyright 2019 The Android Open Source Project
+
+USE_DEVMEM(NEWTOY(devmem, "<1>3", TOYFLAG_USR|TOYFLAG_BIN))
+
+config DEVMEM
+  bool "devmem"
+  default n
+  help
+    usage: devmem ADDR [WIDTH [DATA]]
+
+    Read/write physical address via /dev/mem.
+
+    WIDTH is 1, 2, 4, or 8 bytes (default 4).
+*/
+
+#define FOR_devmem
+#include "toys.h"
+
+void devmem_main(void)
+{
+  int writing = toys.optc == 3, page_size = getpagesize(), bytes = 4, fd;
+  unsigned long long addr = atolx(toys.optargs[0]), data = 0, map_off, map_len;
+  void *map, *p;
+
+  // WIDTH?
+  if (toys.optc>1) {
+    int i;
+
+    if (strlen(toys.optargs[1])!=1 || (i=stridx("1248", *toys.optargs[1]))==-1)
+      error_exit("bad width: %s", toys.optargs[1]);
+    bytes = 1<<i;
+  }
+
+  // DATA? Report out of range values as errors rather than truncating.
+  if (writing) data = atolx_range(toys.optargs[2], 0, (1ULL<<(8*bytes))-1);
+
+  // Map in just enough.
+  fd = xopen("/dev/mem", (writing ? O_RDWR : O_RDONLY) | O_SYNC);
+  map_off = addr & ~(page_size - 1);
+  map_len = (addr+bytes-map_off);
+  map = xmmap(NULL, map_len, writing ? PROT_WRITE : PROT_READ, MAP_SHARED, fd,
+      map_off);
+  p = map + (addr & (page_size - 1));
+  close(fd);
+
+  if (writing) {
+    if (bytes == 1) *(char *)p = data;
+    else if (bytes == 2) *(short *)p = data;
+    else if (bytes == 4) *(int *)p = data;
+    else if (bytes == 8) *(long long *)p = data;
+  } else {
+    if (bytes == 1) data = *(char *)p;
+    else if (bytes == 2) data = *(short *)p;
+    else if (bytes == 4) data = *(int *)p;
+    else if (bytes == 8) data = *(long long *)p;
+    printf("%#0*llx\n", bytes*2, data);
+  }
+
+  munmap(map, map_len);
+}