On 6/13/05, Wolfgang Denk wd@denx.de wrote:

In message c166aa9f05061220474bc0d039@mail.gmail.com you wrote:

...

I noticed on my board that if I enter a space and then return at the u-boot command line I get an exception. I using u-boot from cvs and the standard (not hush) parser on a mips platform. Does anybody else see this behaviour?

You should see a "Unknown command '<NULL>' - try 'help'" error message.

Did you try it?

I dug a bit more and what I found was that in run_command() the parse_line() function eats the leading whitespace then doesn't see anything it recognizes, so sets argv[0] to NULL and returns a zero. The null pointer gets passed to find_cmd() which happily dereferences it and the cpu throws an exception.

Below is the output of main with DEBUG_PARSER turned on (and a printf of argc and *argv I added before the call to find_cmd():

AMR boot# [RUN_COMMAND] cmd[83ff8bc0]=" " [PROCESS_SEPARATORS] token: " " [PROCESS_MACROS] INPUT len 1: " " [PROCESS_MACROS] OUTPUT len 1: " " parse_line: " " parse_line: nargs=0 argc 0 *argv 0 Unhandled exception

$ 0 : 00000000 b1100000 00000000 00000004 $ 4 : 83ff2748 83eefb78 0000000a fffffffb $ 8 : ffffffff 83eefb7e 00000002 00000000 $12 : 00000000 00000000 83ff6d10 00000020 $16 : 83eefcb8 00000000 83eefcb9 83eefdb8 $20 : 00000000 00000000 83eefeb8 00000001 $24 : 3afe5cff 83feff2c $28 : 83ff8050 83eefca0 281925aa 83fdb130 Hi : 00000001 Lo : 00000000 epc : 83fdb144 ra : 83fdb130 Status: 00400002 KERNEL EXL Cause : 00800008 BadVA : 00000000 PrId : 03030200

Attached is a fix which checks if the value of argc is zero before calling find_cmd() and continues.

CHANGELOG: * Patch by Andrew Dyer, 13 June2005: add test to see if no valid commands were found in input string before passing string to find_cmd()