Re: [PATCH v5 03/17] xenctx: Add -n (--display-stack-pages) option to output larger stack

[Don Slutz <dslutz@verizon.com>]

On 03/21/14 10:29, Ian Campbell wrote:
> On Thu, 2014-03-20 at 15:06 -0400, Don Slutz wrote:
>> From: Don Slutz <Don@CloudSwitch.com>
>>
>> Important: This is the stack size to display not the configured
>> stack size.
>>
>> Note: use with caution (easy to get garbage).
>>
>> Below is various pictures of a configured 3 page stack, and where
>> the SP currently is.  Each box is a page.
>>
>>         +------------------+
>>         |                  |
>>         |                  |
>>         |                  |
>>         |                  |
>>         |                  |
>>         +------------------+
>>         |                  |
>>         |                  |
>>         |                  |
>>         |                  |
>>         |                  |
>>         +------------------+
>>         |                  |
>>         |                  |
>>         |                  |
>> SP --> |                  |
>>         |                  |
>>         +------------------+
>>
>> Display using "-n 1" since the used stack pages is 1.
> Like George I am also confused by what these diagrams are trying to show
> me, and even having read your response to him I'm confused.

Let me try again.

Here is real output for a kernel with 4 page stacks:

tools/xentrace/xenctx -s ~/zzm 4 -n 1
rip: ffffffff81346876 io_serial_in+0x16
flags: 00000002 nz
rsp: ffff8800385a5ab8
rax: 000000000000006f   rcx: 0000000000000000   rdx: 00000000000003fd
rbx: ffffffff81ff8f00   rsi: 0000000000000005   rdi: ffffffff81ff8f00
rbp: ffff8800385a5ab8    r8: ffffffff81c03a10    r9: 0000000000000080
r10: 0000000000000005   r11: 0000000000000046   r12: 000000000000270f
r13: 0000000000000020   r14: 0000000000000025   r15: ffffffff81346f20
  cs: 0010        ss: 0018        ds: 0000        es: 0000
  fs: 0000 @ 00007f07972f3700
  gs: 0000 @ ffff88000b400000/0000000000000000/
Code (instr addr ffffffff81346876)
48 89 e5 0f 1f 44 00 00 0f b6 4f 41 0f b7 57 08 d3 e6 01 f2 ec <0f> b6 
c0 c9 c3 0f 1f 44 00 00 55


Stack:
  ffff8800385a5ae8 ffffffff81346e64 ffffffff81ff8f00 0000000000000072
  0000000000000064 0000000000000025 ffff8800385a5b08 ffffffff81346f46
  ffffffff81e3e430 ffffffff81ff8f00 ffff8800385a5b48 ffffffff813428de
  ffffffff8100bc0e 0000000000000000 ffffffff81ff8f00 0000000000000001
  0000000000000064 ffffffff81e3e40c ffff8800385a5b98 ffffffff813472ad

Call Trace:
   [<ffffffff81346876>] io_serial_in+0x16 <--
   [<ffffffff81346e64>] wait_for_xmitr+0x24
   [<ffffffff81346f46>] serial8250_console_putchar+0x26
   [<ffffffff813428de>] uart_console_write+0x3e
   [<ffffffff8100bc0e>] apic_timer_interrupt+0xe
   [<ffffffff813472ad>] serial8250_console_write+0xbd
   [<ffffffff8106b8f5>] __call_console_drivers+0x75
   [<ffffffff8106b95a>] _call_console_drivers+0x4a
   [<ffffffff8106be6e>] release_console_sem+0x4e
   [<ffffffff8106c628>] vprintk+0x248
   [<ffffffff814fd363>] printk+0x41


tools/xentrace/xenctx -s ~/zzm 4 -n 2
rip: ffffffff81346876 io_serial_in+0x16
flags: 00000002 nz
rsp: ffff8800385a5ab8
rax: 000000000000006f   rcx: 0000000000000000   rdx: 00000000000003fd
rbx: ffffffff81ff8f00   rsi: 0000000000000005   rdi: ffffffff81ff8f00
rbp: ffff8800385a5ab8    r8: ffffffff81c03a10    r9: 0000000000000080
r10: 0000000000000005   r11: 0000000000000046   r12: 000000000000270f
r13: 0000000000000020   r14: 0000000000000025   r15: ffffffff81346f20
  cs: 0010        ss: 0018        ds: 0000        es: 0000
  fs: 0000 @ 00007f07972f3700
  gs: 0000 @ ffff88000b400000/0000000000000000/
Code (instr addr ffffffff81346876)
48 89 e5 0f 1f 44 00 00 0f b6 4f 41 0f b7 57 08 d3 e6 01 f2 ec <0f> b6 
c0 c9 c3 0f 1f 44 00 00 55


Stack:
  ffff8800385a5ae8 ffffffff81346e64 ffffffff81ff8f00 0000000000000072
  0000000000000064 0000000000000025 ffff8800385a5b08 ffffffff81346f46
  ffffffff81e3e430 ffffffff81ff8f00 ffff8800385a5b48 ffffffff813428de
  ffffffff8100bc0e 0000000000000000 ffffffff81ff8f00 0000000000000001
  0000000000000064 ffffffff81e3e40c ffff8800385a5b98 ffffffff813472ad

Call Trace:
   [<ffffffff81346876>] io_serial_in+0x16 <--
   [<ffffffff81346e64>] wait_for_xmitr+0x24
   [<ffffffff81346f46>] serial8250_console_putchar+0x26
   [<ffffffff813428de>] uart_console_write+0x3e
   [<ffffffff8100bc0e>] apic_timer_interrupt+0xe
   [<ffffffff813472ad>] serial8250_console_write+0xbd
   [<ffffffff8106b8f5>] __call_console_drivers+0x75
   [<ffffffff8106b95a>] _call_console_drivers+0x4a
   [<ffffffff8106be6e>] release_console_sem+0x4e
   [<ffffffff8106c628>] vprintk+0x248
   [<ffffffff814fd363>] printk+0x41


tools/xentrace/xenctx -s ~/zzm 4 -n 3
rip: ffffffff81346876 io_serial_in+0x16
flags: 00000002 nz
rsp: ffff8800385a5ab8
rax: 000000000000006f   rcx: 0000000000000000   rdx: 00000000000003fd
rbx: ffffffff81ff8f00   rsi: 0000000000000005   rdi: ffffffff81ff8f00
rbp: ffff8800385a5ab8    r8: ffffffff81c03a10    r9: 0000000000000080
r10: 0000000000000005   r11: 0000000000000046   r12: 000000000000270f
r13: 0000000000000020   r14: 0000000000000025   r15: ffffffff81346f20
  cs: 0010        ss: 0018        ds: 0000        es: 0000
  fs: 0000 @ 00007f07972f3700
  gs: 0000 @ ffff88000b400000/0000000000000000/
Code (instr addr ffffffff81346876)
48 89 e5 0f 1f 44 00 00 0f b6 4f 41 0f b7 57 08 d3 e6 01 f2 ec <0f> b6 
c0 c9 c3 0f 1f 44 00 00 55


Stack:
  ffff8800385a5ae8 ffffffff81346e64 ffffffff81ff8f00 0000000000000072
  0000000000000064 0000000000000025 ffff8800385a5b08 ffffffff81346f46
  ffffffff81e3e430 ffffffff81ff8f00 ffff8800385a5b48 ffffffff813428de
  ffffffff8100bc0e 0000000000000000 ffffffff81ff8f00 0000000000000001
  0000000000000064 ffffffff81e3e40c ffff8800385a5b98 ffffffff813472ad

Call Trace:
   [<ffffffff81346876>] io_serial_in+0x16 <--
   [<ffffffff81346e64>] wait_for_xmitr+0x24
   [<ffffffff81346f46>] serial8250_console_putchar+0x26
   [<ffffffff813428de>] uart_console_write+0x3e
   [<ffffffff8100bc0e>] apic_timer_interrupt+0xe
   [<ffffffff813472ad>] serial8250_console_write+0xbd
   [<ffffffff8106b8f5>] __call_console_drivers+0x75
   [<ffffffff8106b95a>] _call_console_drivers+0x4a
   [<ffffffff8106be6e>] release_console_sem+0x4e
   [<ffffffff8106c628>] vprintk+0x248
   [<ffffffff814fd363>] printk+0x41
   [<ffffffff8100204c>] do_one_initcall+0x3c
   [<ffffffff810b0eb1>] sys_init_module+0xe1
   [<ffffffff8100b0f2>] system_call_fastpath+0x16



As you can see from above, only the last 3 lines show up for "-n 3"


>
> Why is the SP moving around in these pictures? I understood that this
> option was changing what was considered to be the limit of the stack,
> not the stack pointer itself, so shouldn't it be the base of the stack
> which is moving around?

These are pictures of the same stack at 3 different times.  And as you 
can see
from above, this option does change the stack limit.


>
> Perhaps if you had the diagram once and along side it had columns
> showing what is printed for each -n value as a range
>
> e.g.
>                                None     -n 1
>         +------------------+              +
>         |                  |              |
>         |                  |              |
>         |                  |              |
>         |                  |              |
>         |                  |              |
>         +------------------+     +        |
>         |                  |     |        |
> SP --> |                  |     +        +
>         |                  |
>         |                  |
>         |                  |
>         +------------------+
>
> (or whatever the reality is)
>
> [...]

I will add this.  And some statement about each picture is for a 
different time.

>> Signed-off-by: Don Slutz <Don@CloudSwitch.com>
> Out of date?

Yes, and no.  Both email continue to work.  I will update it.

>> ---
>> v5: Adjust option to -n, --display-stack-pages.  Adjust usage message.
>>
>>   tools/xentrace/xenctx.c | 12 +++++++++++-
>>   1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/xentrace/xenctx.c b/tools/xentrace/xenctx.c
>> index 42a47f3..caa8899 100644
>> --- a/tools/xentrace/xenctx.c
>> +++ b/tools/xentrace/xenctx.c
>> @@ -35,6 +35,7 @@ static struct xenctx {
>>       int frame_ptrs;
>>       int stack_trace;
>>       int disp_all;
>> +    int multiple_pages;
>>       int all_vcpus;
>>       int self_paused;
>>       xc_dominfo_t dominfo;
>> @@ -664,6 +665,8 @@ static int print_stack(vcpu_guest_context_any_t *ctx, int vcpu, int width)
>>   
>>       stack_limit = ((stack_pointer(ctx) + XC_PAGE_SIZE)
>>                      & ~((guest_word_t) XC_PAGE_SIZE - 1));
>> +    if ( xenctx.multiple_pages > 1 )
>> +        stack_limit += (xenctx.multiple_pages - 1) * XC_PAGE_SIZE;
> "multiple_pages" sounds like a boolean to me, you seem to use it as
> "extra_pages", but why not just call it nr_stack_pages, initialise it to
> 1 and override it with --display-stack-pages.

I will adjust the internal name also.  No idea why I did not do so when 
to option name was changed.

    -Don Slutz

> Ian.
>