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[Bug tapsets/12500] ptrace decoder
- From: "dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sources dot redhat dot com
- Date: Thu, 24 Feb 2011 19:06:03 +0000
- Subject: [Bug tapsets/12500] ptrace decoder
- Auto-submitted: auto-generated
- References: <bug-12500-1110@http.sourceware.org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=12500
David Smith <dsmith at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |dsmith at redhat dot com
--- Comment #1 from David Smith <dsmith at redhat dot com> 2011-02-24 19:05:45 UTC ---
I've taken a look at the patch. Here are some comments:
1) On x86_64 RHEL5 (2.6.18-238.1.1.el5), the following come up as undefined:
PTRACE_SINGLEBLOCK, PTRACE_GETREGSET, and PTRACE_SETREGSET.
On ia64 RHEL5 (2.6.18-194.26.1.el5), the following come up as undefined:
PTRACE_GETREGSET and PTRACE_SETREGSET.
It looks like on RHEL5, PTRACE_[GS]ETREGS is used instead of
PTRACE_[GS]ETREGSET.
2) I'm not too fond of the following style of code in
tapset/powerpc/syscalls.stp:
====
function _arch_ptrace(request,pid,addr,data)
{
if (request == %{ PTRACE_GETVRREGS %})
// TODO: Retrieve *data in .return
return sprintf ("PTRACE_GETVRREGS, %d, data=%p", pid, data)
# ... stuff deleted ...
%{
#ifndef PPC_PTRACE_GETHWDBGINFO
# define PPC_PTRACE_GETHWDBGINFO 0x89
#endif
1 %}
if (request == %{ PPC_PTRACE_GETHWDBGINFO %})
// TODO: Retrieve *data in .return
return sprintf ("PPC_PTRACE_GETHWDBGINFO, %d, data=%p", pid, data)
# ... stuff deleted ...
}
====
I'm not sure we envisioned using the inline embedded-C expressions that way.
Instead I'd suggest something like the following (note that I haven't actually
tried this):
====
%{
#ifndef PPC_PTRACE_GETHWDBGINFO
# define PPC_PTRACE_GETHWDBGINFO 0x89
#endif
%}
function _arch_ptrace(request,pid,addr,data)
{
if (request == %{ PTRACE_GETVRREGS %})
// TODO: Retrieve *data in .return
return sprintf ("PTRACE_GETVRREGS, %d, data=%p", pid, data)
# ... stuff deleted ...
if (request == %{ PPC_PTRACE_GETHWDBGINFO %})
// TODO: Retrieve *data in .return
return sprintf ("PPC_PTRACE_GETHWDBGINFO, %d, data=%p", pid, data)
# ... stuff deleted ...
}
====
You lose a bit of locality, but gain a bit of readability (and don't have to
use a fake return value from the inline embedded-C expression).
3) I'd probably move most of the new code in the syscall.ptrace probe itself to
an auxiliary function, so that nd_syscall.ptrace could share it also.
4) Code like this:
====
probe syscall.ptrace = kernel.function("sys_ptrace").call ?
{
name = "ptrace"
request = $request
pid = $pid
addr = $addr
data = $data
argstr=_arch_ptrace(request,pid,addr,data)
====
is better expressed as:
probe syscall.ptrace = kernel.function("sys_ptrace").call ?
{
name = "ptrace"
request = $request
pid = $pid
addr = $addr
data = $data
argstr=_arch_ptrace($request,$pid,$addr,$data)
====
By using the dwarf variables directly, the optimizer has an easier time getting
rid of unused convenience variables. (Feel free to use a convenience variable
when getting the convenience variable value is complicated.)
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