binarybuffer: Fix str_to_buf() parsing function

The function str_to_buf() was too benevolent and did
not perform sufficient error checking on the input
string being parsed. Especially:

- Invalid numbers were silently ignored.
- Out-of-range numbers were silently truncated.

The following commands that use str_to_buf()
were affected:

- reg (when writing a register value)
- set_reg
- jtag drscan

This pull request fixes that by:

- Rewriting str_to_buf() to add the missing checks.
- Adding function command_parse_str_to_buf() which can
  be used in command handlers. It parses the input
  numbers and provides user-readable error messages
  in case of parsing errors.

Examples:

jtag drscan 10 huh10

- Old behavior: The string "huh10" is silently
  converted to 10 and the command is then executed.
  No warning error or warning is shown to the user.
- New behavior: Error message is shown:
  "'huh10' is not a valid number"

reg pc 0x123456789

Assuming the "pc" is 32 bits wide:

- Old behavior: The register value is silently
  truncated to 0x23456789 and the command is performed.
- New behavior: Error message is shown to the user:
  "Number 0x123456789 exceeds 32 bits"

Change-Id: I079e19cd153aec853a3c2eb66953024b8542d0f4
Signed-off-by: Jan Matyas <jan.matyas@codasip.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8315
Tested-by: jenkins
Reviewed-by: Marek Vrbka <marek.vrbka@codasip.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/helper/command.h

@@ -517,6 +517,17 @@ DECLARE_PARSE_WRAPPER(_target_addr, target_addr_t);
 int command_parse_bool_arg(const char *in, bool *out);
 COMMAND_HELPER(handle_command_parse_bool, bool *out, const char *label);
 
+/**
+ * Parse a number (base 10, base 16 or base 8) and store the result
+ * into a bit buffer.
+ *
+ * In case of parsing error, a user-readable error message is produced.
+ *
+ * If radix = 0 is given, the function guesses the radix by looking at the number prefix.
+ */
+COMMAND_HELPER(command_parse_str_to_buf, const char *str, void *buf, unsigned int buf_len,
+	unsigned int radix);
+
 /** parses an on/off command argument */
 #define COMMAND_PARSE_ON_OFF(in, out) \
 	COMMAND_PARSE_BOOL(in, out, "on", "off")