Gdbserver syscall clobber

Bill Gatliff bgat at
Tue Jul 24 02:06:13 EST 2007

Daniel Jacobowitz wrote:
> On Wed, Jul 18, 2007 at 12:59:42PM -0500, Bill Gatliff wrote:
>> Now, I'm a little rusty on PPC asm (I've been doing a lot of ARM
>> lately), but it looks to me like the kernel is setting bit 0 in CR0
>> (oris r10, r10, 0x1000) a.k.a LT, but the user side is looking at CR0
>> (bnslr+) bit 3 a.k.a. SO.  Or maybe the other way around, I'm not sure
>> after reading Sections 1.2 and 2.1 of the Programming Environments manual.
> It's not checking for restart here - userspace isn't supposed to have to.
> It's probably checking for error.  Check for the bit of kernel code
> that's supposed to back you up two instructions.

I don't see it in this kernel.  What I see is this after the call to the 
syscall handler:

    li    r10,-_LAST_ERRNO
    cmpl    0,r3,r10
    blt    30f
    neg    r3,r3
    cmpi    0,r3,ERESTARTNOHAND
    bne    22f
    li    r3,EINTR
22:    lwz    r10,_CCR(r1)    /* Set SO bit in CR */
    oris    r10,r10,0x1000
    stw    r10,_CCR(r1)
30:    stw    r3,GPR3(r1)    /* Update return value */
    b    ret_from_except
66:    li    r3,ENOSYS
    b    22b


Bill Gatliff
bgat at

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