[Bug kprobes/2945] New: cannot probe vgettimeofday on x86_64

[Bug kprobes/2945] New: cannot probe vgettimeofday on x86_64

[hunt at redhat dot com]

> uname -a
Linux tiger 2.6.9-42.ELsmp #1 SMP Wed Jul 12 23:32:02 EDT 2006 x86_64 x86_64
x86_64 GNU/Linux

> stap -e 'probe kernel.function("vgettimeofday") {}'
ERROR: probe 0 registration failed, rc=1,
kernel.function("vgettimeofday@arch/x86_64/kernel/vsyscall.c:126")

-- 
           Summary: cannot probe vgettimeofday on x86_64
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: kprobes
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: hunt at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=2945

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[Bug kprobes/2945] cannot probe vgettimeofday on x86_64

[bibo dot mao at intel dot com]

------- Additional Comments From bibo dot mao at intel dot com  2006-07-21 06:19 -------
vgettimeofday can be called by application in user mode, now in x86_64 function 
address of vgettimeofday is outside of kernel_text_address() scope, so it 
failed to register kprobe for this function.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=2945

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[Bug kprobes/2945] cannot probe vgettimeofday on x86_64

[jkenisto at us dot ibm dot com]

------- Additional Comments From jkenisto at us dot ibm dot com  2006-11-16 01:25 -------
Consider allowing probes on weird locations like i386 vtoc page, x86_64
.vsyscall_ section, etc.

-- 


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[Bug kprobes/2945] cannot probe vgettimeofday on x86_64

[jkenisto at us dot ibm dot com]

------- Additional Comments From jkenisto at us dot ibm dot com  2006-11-16 18:07 -------
Further thoughts:
- vdso, not vtoc. (Haste and advanced age are a bad combo. :-})
- Since a kprobed instruction is copied into a kernel-space buffer and
single-stepped there, we do NOT want to allow kprobes on instructions that are
executed in user mode, such as on the vdso page.

-- 


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[Bug kprobes/2945] cannot probe vgettimeofday on x86_64

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2006-11-16 23:37 -------
(In reply to comment #3)
> [...]
> - Since a kprobed instruction is copied into a kernel-space buffer and
> single-stepped there, we do NOT want to allow kprobes on instructions that are
> executed in user mode, such as on the vdso page.

Good point.  We should leave vdso type probes to user-space probing.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


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