asm code

asm code

[Chris Friesen]

I'm trying to do an indirect address lookup in entry.S.  I've added a
lookup table at the end of entry.S as follows:

hrt_ak_offsets:
	.byte HRT_AK_USER_USER_SYNC
	.byte HRT_AK_SIGM_USER_SYNC
	.byte HRT_AK_SIGU_USER_SYNC
	.byte HRT_AK_USER_SIG_SYNC
	.byte HRT_AK_SIGM_SIG_SYNC
	.byte HRT_AK_SIGU_SIG_SYNC
	.byte HRT_AK_USER_USER_ASYN
	.byte HRT_AK_SIGM_USER_ASYN
<etc...>

I then have some code that wants to load up one of these values and use
it as an offset into another struct.  Coming into the following stretch
of code, r6 contains the entry number within hrt_ak_offsets, and r4
contains the base address of the other struct.

	lis	r5,hrt_ak_offsets@ha
	addi	r5,r5,hrt_ak_offsets@l
	lbzx	r6,r6,r5
	add	r10,r4,r6

I'm having a small problem, in that when I run this code it hangs my
kernel.  Any ideas what's wrong?  The values in r6 and r5 seem to match
what I expect, but when I do the lbzx it dies.

Thanks,

Chris

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Re: help with asm code?

[Benjamin Herrenschmidt]

> I then have some code that wants to load up one of these values and use
> it as an offset into another struct.  Coming into the following stretch
> of code, r6 contains the entry number within hrt_ak_offsets, and r4
> contains the base address of the other struct.
>
>
> 	lis	r5,hrt_ak_offsets@ha
> 	addi	r5,r5,hrt_ak_offsets@l
> 	lbzx	r6,r6,r5
> 	add	r10,r4,r6
>
>
> I'm having a small problem, in that when I run this code it hangs my
> kernel.  Any ideas what's wrong?  The values in r6 and r5 seem to match
> what I expect, but when I do the lbzx it dies.

I don't know for sure, maybe you MMU context is wrong at the time ?
(Assuming a 32 bits kernel, a 64 bits kernel need more instructions
to load the address)

How do you know it dies there and not elsewhere ?


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Re: help with asm code?

[Chris Friesen]

Benjamin Herrenschmidt wrote:

>>	lis	r5,hrt_ak_offsets@ha
>>	addi	r5,r5,hrt_ak_offsets@l
>>	lbzx	r6,r6,r5
>>	add	r10,r4,r6
>>
>>
>>I'm having a small problem, in that when I run this code it hangs my
>>kernel.  Any ideas what's wrong?  The values in r6 and r5 seem to match
>>what I expect, but when I do the lbzx it dies.
>
>
> I don't know for sure, maybe you MMU context is wrong at the time ?

The code is being called from fast_exception_return, syscall_exit_cont,
and restore_user.

> How do you know it dies there and not elsewhere ?

If I remove the lbzx/add lines, everything works fine.  With the lbzx
line it dies, even if r10 is overwritten right away.

Chris

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Re: help with asm code?

[Benjamin Herrenschmidt]

> The code is being called from fast_exception_return, syscall_exit_cont,
> and restore_user.
>
> > How do you know it dies there and not elsewhere ?
>
> If I remove the lbzx/add lines, everything works fine.  With the lbzx
> line it dies, even if r10 is overwritten right away.

You'd have to send me the whole exception code path so I can figure
out what's up

Ben.


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