Re: Breakage in arch/mips/kernel/traps.c for 64bit

[Atsushi Nemoto <anemo@xxxxxxxxxxxxx>]

On Mon, 5 May 2008 00:08:04 +0200, tsbogend@xxxxxxxxxxxxxxxx (Thomas Bogendoerfer) wrote:
> > 	while (!kstack_end((void *)(unsigned long)sp)) {
> > 
> > will make this part sparse-free, though it seems a bit ugly.
> 
> hmm, would leaving sp as unsigned long * and casting it for __get_user()
> make sparse happy ?

Well, not as expected...  Here is some warning patterns.

1.	unsigned long __user *sp = (unsigned long __user *)(reg29 & ~3);
	...
	while (!kstack_end(sp)) {
		if (__get_user(addr, sp++)) {

linux/arch/mips/kernel/traps.c:91:21: warning: incorrect type in argument 1 (different address spaces)
linux/arch/mips/kernel/traps.c:91:21:    expected void *addr
linux/arch/mips/kernel/traps.c:91:21:    got unsigned long [noderef] <asn:1>*sp

2.	unsigned long *sp = (unsigned long *)(reg29 & ~3);
	...
	while (!kstack_end(sp)) {
		if (__get_user(addr, (unsigned long __user *)sp++)) {

linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)
linux/arch/mips/kernel/traps.c:92:7: warning: cast adds address space to expression (<asn:1>)

3.	unsigned long __user *sp = (unsigned long __user *)(reg29 & ~3);
	...
	while (!kstack_end((void *)(unsigned long)sp)) {
		if (__get_user(addr, sp++)) {

No warnings.

4.	unsigned long *sp = (unsigned long *)(reg29 & ~3);
	...
	while (!kstack_end(sp)) {
		unsigned long __user *p = (unsigned long __user *)sp++;
		if (__get_user(addr, p)) {

linux/arch/mips/kernel/traps.c:92:30: warning: cast adds address space to expression (<asn:1>)

4.	unsigned long *sp = (unsigned long *)(reg29 & ~3);
	...
	while (!kstack_end(sp)) {
		unsigned long __user *p =
			(unsigned long __user *)(unsigned long)sp++;
		if (__get_user(addr, p)) {

No warnings.


I think the "cast adds address space to expression" sparse warning is
not worth to handle so seriously.  So I'm OK with any of (2) to (4).

---
Atsushi Nemoto