[PATCH] i386:kexec-bzImage: Use "\0" as command line instead of empty command line

[Zhang Yanfei]

于 2013年04月08日 14:07, Wang YanQing 写道:
> On Mon, Apr 08, 2013 at 12:33:40PM +0800, Zhang Yanfei wrote:
>> I think this is ok for we have filled all the real_mode buffer with 0.
> I don't think so, it must be somethings wrong, if we had filled all
> the real_mode buffer with 0, why do we need my patch to set 
> the string termination guard '\0'? 

real_mode = kernel16 buf + commandline + purgatory commandline.

At first, we filled all real_mode buffer with 0, then we assigned values
to kernel16 buf just in the head of real_mode.
And next, we copied the commandline just after the kernel16 buf. Usually,
when we copy a string into a buffer, we will set the string termination
guard '\0' right after the string in the buffer for safety, I think.

As your patch, If we have no commandline, and just assign it to '\0'. It
prevents the problems to happen below:

In setup_linux_bootloader_parameters_high

120         cmdline_ptr = ((char *)real_mode) + cmdline_offset;
121         memcpy(cmdline_ptr, cmdline, cmdline_len);
122         cmdline_ptr[cmdline_len - 1] = '\0';

if cmdline_len == 0, Line 122 will corrupt kernel16 buf just before the commandline.

And in do_bzImage_load, for example,

369         cmdline_end = setup_base + kern16_size_needed + command_line_len - 1;
370         elf_rel_set_symbol(&info->rhdr, "cmdline_end", &cmdline_end,
371                            sizeof(unsigned long));

Line 369 will go wrong, too.

> 
> Does '\0' equal zero, right?

Yeah, if we write '\0', the value store into the char buf is zero, I think.

Correct me if I am wrong, please.

Thanks
Zhang