[Crash-utility] Getting access to function parameters

[Ahmed Al-Mehdi]

Hello,

I have a question about trying to decipher the values of parameters passed
to a function in "crash".  I understand "bt -f" and "bt -F" prints the
 stack data, but I am having a hard time deciphering the stack to get
access to the values of parameters passed to a function.  I understand the
compiler could have optimized the parameters into registers.  If so, is
there a compiler option to turn it off?  If not, is my only option to
browse the object file to see what registers are used?  Is there any
extensions (experimental or hack) that I can add to crash to display
function parameter values.

In the following crash, I am trying to understand the value of the function
parameters - e, buf, len.  Any help or pointers would be very appreciated.



c code:

int
doread(EB *e, uchar *buf, int len)
{
        return queueread(e->rq, buf, len);
}

>From crash:

crash> bt
PID: 2725   TASK: ffff880353c17500  CPU: 1   COMMAND: "bash"
 #0 [ffff88036276d540] machine_kexec at ffffffff8103281b
 #1 [ffff88036276d5a0] crash_kexec at ffffffff810ba662
 #2 [ffff88036276d670] oops_end at ffffffff81501290
 #3 [ffff88036276d6a0] no_context at ffffffff81043bab
 #4 [ffff88036276d6f0] __bad_area_nosemaphore at ffffffff81043e35
 #5 [ffff88036276d740] bad_area at ffffffff81043f5e
 #6 [ffff88036276d770] __do_page_fault at ffffffff81044710
 #7 [ffff88036276d890] do_page_fault at ffffffff8150326e
 #8 [ffff88036276d8c0] page_fault at ffffffff81500625
    [exception RIP: queueread+32]
    RIP: ffffffffa03e4b70  RSP: ffff88036276d978  RFLAGS: 00010286
    RAX: 00000000000005ae  RBX: 0000000000000000  RCX: 0000000000000000
    RDX: 0000000000001000  RSI: ffff8803613c0020  RDI: 0000000000000000
    RBP: ffff88036276d9a8   R8: 0000000000000d44   R9: 0000000050c91762
    R10: 0000000000000000  R11: 0000000000000000  R12: ffff8803613c0020
    R13: ffff880341780290  R14: 00000000000237f8  R15: ffff880341780020
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
 #9 [ffff88036276d9b0] elread at ffffffffa03ecd25 [ethdrv]
#10 [ffff88036276d9c0] elechosrv at ffffffffa03eef4d [ethdrv]
#11 [ffff88036276da00] edwritectl at ffffffffa03dff0e [ethdrv]
#12 [ffff88036276de40] writectl at ffffffffa03f028b [ethdrv]
#13 [ffff88036276de60] proc_file_write at ffffffff811e6e44
#14 [ffff88036276dea0] proc_reg_write at ffffffff811e0abe
#15 [ffff88036276def0] vfs_write at ffffffff8117b068
#16 [ffff88036276df30] sys_write at ffffffff8117ba81
#17 [ffff88036276df80] system_call_fastpath at ffffffff8100b0f2
    RIP: 0000003a29ada3c0  RSP: 00007fffe92f1a60  RFLAGS: 00010202
    RAX: 0000000000000001  RBX: ffffffff8100b0f2  RCX: 0000000000000065
    RDX: 000000000000000a  RSI: 00007fab2c281000  RDI: 0000000000000001
    RBP: 00007fab2c281000   R8: 000000000000000a   R9: 00007fab2c272700
    R10: 00000000fffffff7  R11: 0000000000000246  R12: 000000000000000a
    R13: 0000003a29d8c780  R14: 000000000000000a  R15: 0000000000e75130
    ORIG_RAX: 0000000000000001  CS: 0033  SS: 002b


crash> bt -f
..............
 #8 [ffff88036276d8c0] page_fault at ffffffff81500625
    [exception RIP: queueread+32]
    RIP: ffffffffa03e4b70  RSP: ffff88036276d978  RFLAGS: 00010286
    RAX: 00000000000005ae  RBX: 0000000000000000  RCX: 0000000000000000
    RDX: 0000000000001000  RSI: ffff8803613c0020  RDI: 0000000000000000
    RBP: ffff88036276d9a8   R8: 0000000000000d44   R9: 0000000050c91762
    R10: 0000000000000000  R11: 0000000000000000  R12: ffff8803613c0020
    R13: ffff880341780290  R14: 00000000000237f8  R15: ffff880341780020
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
    ffff88036276d8c8: ffff880341780020 00000000000237f8
    ffff88036276d8d8: ffff880341780290 ffff8803613c0020
    ffff88036276d8e8: ffff88036276d9a8 0000000000000000
    ffff88036276d8f8: 0000000000000000 0000000000000000
    ffff88036276d908: 0000000050c91762 0000000000000d44
    ffff88036276d918: 00000000000005ae 0000000000000000
    ffff88036276d928: 0000000000001000 ffff8803613c0020
    ffff88036276d938: 0000000000000000 ffffffffffffffff
    ffff88036276d948: ffffffffa03e4b70 0000000000000010
    ffff88036276d958: 0000000000010286 ffff88036276d978
    ffff88036276d968: 0000000000000018 ffffffffa03ed062
    ffff88036276d978: 000005ae613c01ab ffff880341780290
    ffff88036276d988: 00000000000005ae ffff8803613c0020
    ffff88036276d998: ffff880341780290 00000000000237f8
    ffff88036276d9a8: ffff88036276d9b8 ffffffffa03ecd25
 #9 [ffff88036276d9b0] elread at ffffffffa03ecd25 [ethdrv]
    ffff88036276d9b8: ffff88036276d9f8 ffffffffa03eef4d
...................

crash> bt -F
 #8 [ffff88036276d8c0] page_fault at ffffffff81500625
    [exception RIP: queueread+32]
    RIP: ffffffffa03e4b70  RSP: ffff88036276d978  RFLAGS: 00010286
    RAX: 00000000000005ae  RBX: 0000000000000000  RCX: 0000000000000000
    RDX: 0000000000001000  RSI: ffff8803613c0020  RDI: 0000000000000000
    RBP: ffff88036276d9a8   R8: 0000000000000d44   R9: 0000000050c91762
    R10: 0000000000000000  R11: 0000000000000000  R12: ffff8803613c0020
    R13: ffff880341780290  R14: 00000000000237f8  R15: ffff880341780020
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
    ffff88036276d8c8: [size-131072]    00000000000237f8
    ffff88036276d8d8: [size-131072]    [size-8192]
    ffff88036276d8e8: ffff88036276d9a8 0000000000000000
    ffff88036276d8f8: 0000000000000000 0000000000000000
    ffff88036276d908: 0000000050c91762 0000000000000d44
    ffff88036276d918: 00000000000005ae 0000000000000000
    ffff88036276d928: 0000000000001000 [size-8192]
    ffff88036276d938: 0000000000000000 ffffffffffffffff
    ffff88036276d948: queueread+32         0000000000000010
    ffff88036276d958: 0000000000010286 ffff88036276d978
    ffff88036276d968: 0000000000000018 elwrite+98
    ffff88036276d978: 000005ae613c01ab [size-131072]
    ffff88036276d988: 00000000000005ae [size-8192]
    ffff88036276d998: [size-131072]    00000000000237f8
    ffff88036276d9a8: ffff88036276d9b8 elread+21
 #9 [ffff88036276d9b0] elread at ffffffffa03ecd25 [ethdrv]
    ffff88036276d9b8: ffff88036276d9f8 elechosrv+173
........................

Regards,
Ahmed.
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