[PATCH]kexec:i386:kexec-bzImage: Fix pass garbage command line to new kernel

[Wang YanQing]

I get garbage output of /proc/cmdline and in dmesg in new
kernel context when I use kexec to load new kernel bzImage
without append command line like below:

kexec -l bzImage --initrd=/boot/initramfs
kexec -e

The reason is kernel copy the command line
from the bootloader like below which copy/paste
from linux/arch/x86/kernel/head_32.S:

        movl pa(boot_params) + NEW_CL_POINTER,%esi
        andl %esi,%esi
        jz 1f                   # No command line
        movl $pa(boot_command_line),%edi
        movl $(COMMAND_LINE_SIZE/4),%ecx

This patch fix it.

[
although another patch
"kexec:i386/kexec-[bzImage|elf-x86]:x86_64/kexec-bzImage64: Use "\0" as command line instead of empty command line"
has resolved the garbage output by put a '\0' at the start, but I thinks this patch has sense too, it stop
kernel copy not command line data into the command line buffer in kernel
]

Signed-off-by: Wang YanQing <udknight at gmail.com>
---
 kexec/arch/i386/kexec-bzImage.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kexec/arch/i386/kexec-bzImage.c b/kexec/arch/i386/kexec-bzImage.c
index 29f280d..13cd3f9 100644
--- a/kexec/arch/i386/kexec-bzImage.c
+++ b/kexec/arch/i386/kexec-bzImage.c
@@ -119,6 +119,7 @@ int do_bzImage_load(struct kexec_info *info,
 	unsigned long cmdline_end;
 	unsigned long kern16_size_needed;
 	unsigned long heap_size = 0;
+	off_t alloc_command_line_len = 0;
 
 	/*
 	 * Find out about the file I am about to load.
@@ -145,10 +146,12 @@ int do_bzImage_load(struct kexec_info *info,
 			dbgprintf("Kernel command line too long for kernel!\n");
 			return -1;
 		}
+		alloc_command_line_len = (uintmax_t)setup_header.cmdline_size;
 	} else {
 		if (command_line_len > 255) {
 			dbgprintf("WARNING: This kernel may only support 255 byte command lines\n");
 		}
+		alloc_command_line_len = 255;
 	}
 
 	if (setup_header.protocol_version >= 0x0205) {
@@ -231,7 +234,7 @@ int do_bzImage_load(struct kexec_info *info,
 		if (kern16_size_needed < 4096)
 			kern16_size_needed = 4096;
 	}
-	setup_size = kern16_size_needed + command_line_len +
+	setup_size = kern16_size_needed + alloc_command_line_len +
 			 PURGATORY_CMDLINE_SIZE;
 	real_mode = xmalloc(setup_size);
 	memset(real_mode, 0, setup_size);
-- 
1.7.12.4.dirty