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From: Oleksandr Tymoshenko <gonzo@FreeBSD.org>
To: Perforce Change Reviews <perforce@FreeBSD.org>
Cc: 
Subject: PERFORCE change 113865 for review
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http://perforce.freebsd.org/chv.cgi?CH=113865

Change 113865 by gonzo@gonzo_jeeves on 2007/02/01 21:40:41

	o In order to have userland binaries respecting ABI call conventions
	    syscall handler should skip first 4 words starting from $sp to get
	    arguments counting from 5th. This chunk of stack is called 
	    "arguments slot" though it carries no actual values. It is just 
	    reserved space which could be filled with $a0..$a4 values by called
	    routine.

Affected files ...

.. //depot/projects/mips2/src/sys/mips/mips/trap.c#15 edit

Differences ...

==== //depot/projects/mips2/src/sys/mips/mips/trap.c#15 (text+ko) ====

@@ -407,8 +407,16 @@
 	/* Copy arguments from stack (if any) */
 	if(i < nargs)
 	{
-		error = copyin((void *)frame->tf_regs[TF_SP], copyargs + i,
-		    (nargs - i) * sizeof(register_t));
+		/* 
+		 * ABI NOTE:
+		 * syscall routine does not modify SP so we should take into
+		 * account "arguments slot" - four words reserved by callee
+		 * for called routine. These words *might* be used by called 
+		 * routine as a store place for $a0..$a3 however content of 
+		 * slot is undefined.
+		 */
+		error = copyin((void *)(frame->tf_regs[TF_SP] + 16),
+		    copyargs + i, (nargs - i) * sizeof(register_t));
 
 		if (error)
 			goto bad;