the weird thing when I deal with the ipc

[taxus]

now I am working on my os about the ipc
I use the message to implement it
I had two system task and three user process
the user process are mostly same, just like this

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void TestA()
{
	while(1){
		printf("A");
		milli_delay(200);
	}
}

The IPC is almost finished,but there is an weird thing :
the first user process (TestA) can't call any function that really do something,but other process can do it well
when I use printf() in TestA ,the exception says " #UD Unvaliable Operate eip 0x10b cs 0x5"
I use bochs to unassemble the code ,got the information below

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0000010b: (                    ): lock pop edx                  ; f05a
0000010d: (                    ): and eax, 0xff53c000       ; 2500c053ff
00000112: (                    ): add al, dh                      ; 00f0
00000114: (                    ): push ebx                       ; 53
00000115: (                    ): inc dword ptr ds:[eax]      ; ff00
00000117: (                    ): lock dec ebp                  ; f04d
00000119: (                    ): add al, al                       ; 00c0
0000011b: (                    ): lahf                               ; 9f
0000011c: (                    ): push ebx                        ; 53
0000011d: (                    ): inc dword ptr ds:[eax]     ; ff00

and the bochs also print these message

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00019680650i[CPU0 ] LOCK prefix unallowed (op1=0x5a, modrm=0x00)
00019681939i[CPU0 ] WARNING: HLT instruction with IF=0!

I had stuck by this problem a week,it's so weird that the problem just appear to TestA
anyone has met this problem before?

[Combuster]

Looks like you're jumping to address 0 (or somewhere close). You're apparently running the BIOS data in the IVT as if it were code.

[Chandra]

#UD Unvaliable Operate eip 0x10b cs 0x5"

And what sort of CS selector is that? Looks like you're messing with the stack.

[taxus]

I check the LDT initial , there is no error about it
when I didn't implement the message IPC ,just use system call,all these process work well
but when I finish IPC, no matter how ,the third process in the proc_table will not work,and other work well,can it eliminate the error of IPC ?
I use the same function to initial all of the process,so......It's so weird

[taxus]

thanks everybody's help
now it works
the reason is I upset down these code

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taskstackpoint -= p_task->stacksize;
p_task++;

the sequence before is

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p_task++;
taskstackpoint -= p_task->stacksize;

that I plus the p_task before I use it
anyway ,thanks everyone