Re: [Fwd: Re: Regarding systemtap support for AArch64]

[William Cohen <wcohen at redhat dot com>]

On 11/04/2013 10:27 AM, Petr Machata wrote:
> Mark Wielaard <mjw@redhat.com> writes:
> 
>> According to the call abi the simple integer value should be in
>> register "x0".  It looks in the generated c code for the module that
>> it is trying to access the return value with:
>>
>>     { int64_t value = fetch_register (0); STAP_RETVALUE = value; }
> 
> Is this using ebl_return_value_location?  That should be on the branch,
> and unless I'm interpreting things wrong, it's doing the right thing:
> 
> $ ./tests/funcretval -e ~/tmp/aarch64-ble
> () fun_char: return value location: {0x50, 0}
> () fun_short: return value location: {0x50, 0}
> () fun_int: return value location: {0x50, 0}
> () fun_ptr: return value location: {0x50, 0}
> () fun_iptr: return value location: {0x50, 0}
> () fun_long: return value location: {0x50, 0}
> () fun_int128: return value location: {0x50, 0} {0x93, 0x8} {0x51, 0} {0x93, 0x8}
> [...]
> 
> I don't think there are any real tests for this in elfutils--such that
> would really check that yes, the values that we expect are in the
> registers that ebl_return_value_location claims.
> 
> An idea that I had was to start a binary that calls a function and
> crashes (br 0?), and then inspect the coredump to see if the values are
> in the registers that elfutils expect.  But that seems cumbersome.  I'm
> reluctant to use ptrace, but that would obviously work as well.
> 
>> As a sanity check I ran a "make -s check" on the locally built aarch64
>> elfutils to see if there were any issues with it.
> 
> Yes, I know of the failures.  The port isn't finished yet.  I had to
> switch gears for some other work.  I'm probably missing a bunch of hooks
> that need implementing, I'm working through them one at a time.
> 
> Thanks,
> PM
> 

Hi Petr,

Thanks for working on the elfutils aarch64 support.

I implemented the print_regs() function for systemtap to print out the various fields in pt_regs.  I have the print_regs() ansl printing out the orig_x0 and syscallno fields also.  The x0 field's value looks questionable as seen below in the short one- line systemtap scripts on the aarch64.  

$ sudo ~/systemtap_write/install/bin/stap  -k -e 'probe vfs.read.return {printf("$return = 0x%x\n", $return);print_regs(); exit()}'
[sudo] password for wcohen: 
$return = 0xffffffc04abe5e00
 CPU: 0
 x0 : FFFFFFC04ABE5E00 0000007FCC574070 0000000000002004 FFFFFFC077CFBEB0 
 x4 : 0000000000000000 0000000000000002 0000000000000000 0000000000000005 
 x8 : 000000000000003F 0000000000000028 0000000000401277 0000007FCC571E70 
 x12: 0000000000000000 0000000000000001 0000007FCC5763B0 0000000000000004 
 x16: FFFFFFC0001868E0 0000007FA3F26A50 0000007FCC571B90 FFFFFFC04ABE5E00 
 x20: 0000007FCC574070 0000000000000001 0000007FA3F26AA8 0000000080000000 
 x24: 0000000000000015 0000000000000112 000000000000003F FFFFFFC000835000 
 x28: FFFFFFC077CF8000 FFFFFFC077CFBE80 FFFFFFC000186924 
sp [ffffffc077cfbe30] pc [ffffffc000186134]
pstate [0000000060000145]
orig_x0 [0000000000000015]
syscallno [0000000000000112]
Keeping temporary directory "/tmp/stap1OWdNi"

$ sudo ~/systemtap_write/install/bin/stap  -k -e 'probe vfs.read {printf("$$parms = %sn", $$parms);print_regs(); exit()}'
[sudo] password for wcohen: 
$$parms = file=0xffffffc04ab83e00 buf=0x7fdaad4290 count=0x2004 pos=0xffffffc043847eb0n CPU: 0
 x0 : FFFFFFC04AB83E00 0000007FDAAD4290 0000000000002004 FFFFFFC043847EB0 
 x4 : 0000000000000000 0000000000000002 0000000000000000 0000000000000005 
 x8 : 000000000000003F 0000000000000028 0000000000401277 0000007FDAAD2090 
 x12: 0000000000000000 0000000000000001 0000007FDAAD65D0 0000000000000004 
 x16: FFFFFFC0001868E0 0000007F7F6E0A50 0000007FDAAD1DB0 FFFFFFC04AB83E00 
 x20: 0000007FDAAD4290 0000000000000001 0000007F7F6E0AA8 0000000080000000 
 x24: 0000000000000015 0000000000000112 000000000000003F FFFFFFC000835000 
 x28: FFFFFFC043844000 FFFFFFC043847E80 FFFFFFC000186924 
sp [ffffffc043847e80] pc [ffffffc000186130]
pstate [0000000060000145]
orig_x0 [0000007fdaad4120]
syscallno [ffffffc000082fec]
Keeping temporary directory "/tmp/stapQI9d6o"

-Will