* [Bug translator/15688] New: Accessing globals in DSO or PIE results in read faults
@ 2013-06-27 2:02 agentzh at gmail dot com
2013-06-27 16:05 ` [Bug translator/15688] " jistone at redhat dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: agentzh at gmail dot com @ 2013-06-27 2:02 UTC (permalink / raw)
To: systemtap
http://sourceware.org/bugzilla/show_bug.cgi?id=15688
Bug ID: 15688
Summary: Accessing globals in DSO or PIE results in read faults
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: translator
Assignee: systemtap at sourceware dot org
Reporter: agentzh at gmail dot com
I've noticed that use of @var("foo") or $foo in either probe process.function
or probe process.mark could lead to the following error when there is a global
variable named "foo" in the current userspace DSO or PIE module:
ERROR: read fault [man error::fault] at 0x (null) (addr) near
operator '@var'
It seems that dwarf_var_expanding_visitor::visit_target_symbol can resolve the
variable into a global variable but does not enable the VMA tracker for the
current module accordingly.
I can always reproduce this with trivial example on the current master (commit
5883b785fa)
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* [Bug translator/15688] Accessing globals in DSO or PIE results in read faults
2013-06-27 2:02 [Bug translator/15688] New: Accessing globals in DSO or PIE results in read faults agentzh at gmail dot com
@ 2013-06-27 16:05 ` jistone at redhat dot com
2013-06-27 19:37 ` agentzh at gmail dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: jistone at redhat dot com @ 2013-06-27 16:05 UTC (permalink / raw)
To: systemtap
http://sourceware.org/bugzilla/show_bug.cgi?id=15688
Josh Stone <jistone at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jistone at redhat dot com
--- Comment #1 from Josh Stone <jistone at redhat dot com> ---
(In reply to agentzh from comment #0)
> I can always reproduce this with trivial example on the current master
Can you state such an example here?
dwflpp::emit_address already calls enable_task_finder for cases which use
_stp_umodule_relocate, but it may be more specific to its needs to call
enable_vma_tracker.
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* [Bug translator/15688] Accessing globals in DSO or PIE results in read faults
2013-06-27 2:02 [Bug translator/15688] New: Accessing globals in DSO or PIE results in read faults agentzh at gmail dot com
2013-06-27 16:05 ` [Bug translator/15688] " jistone at redhat dot com
@ 2013-06-27 19:37 ` agentzh at gmail dot com
2013-06-27 22:17 ` jistone at redhat dot com
2013-06-27 22:51 ` jistone at redhat dot com
3 siblings, 0 replies; 5+ messages in thread
From: agentzh at gmail dot com @ 2013-06-27 19:37 UTC (permalink / raw)
To: systemtap
http://sourceware.org/bugzilla/show_bug.cgi?id=15688
--- Comment #2 from agentzh <agentzh at gmail dot com> ---
Included the corresponding tests in the test file
systemtap.base/sdt_global_var.exp included in my patch here:
http://sourceware.org/ml/systemtap/2013-q2/msg00389.html
Thanks!
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* [Bug translator/15688] Accessing globals in DSO or PIE results in read faults
2013-06-27 2:02 [Bug translator/15688] New: Accessing globals in DSO or PIE results in read faults agentzh at gmail dot com
2013-06-27 16:05 ` [Bug translator/15688] " jistone at redhat dot com
2013-06-27 19:37 ` agentzh at gmail dot com
@ 2013-06-27 22:17 ` jistone at redhat dot com
2013-06-27 22:51 ` jistone at redhat dot com
3 siblings, 0 replies; 5+ messages in thread
From: jistone at redhat dot com @ 2013-06-27 22:17 UTC (permalink / raw)
To: systemtap
http://sourceware.org/bugzilla/show_bug.cgi?id=15688
--- Comment #3 from Josh Stone <jistone at redhat dot com> ---
(In reply to Josh Stone from comment #1)
> dwflpp::emit_address already calls enable_task_finder for cases which use
> _stp_umodule_relocate, but it may be more specific to its needs to call
> enable_vma_tracker.
I tried this suggestion with your testcase, and it did the trick. I think it
will also make this hack from parse_cmdline unnecessary:
// PR10228: trigger vma tracker logic early if -d /USER-MODULE/
// given. XXX This is actually too early. Having a user module
// is a good indicator that something will need vma tracking.
// But it is not 100%, this really should only trigger through
// a user mode tapset /* pragma:vma */ or a probe doing a
// variable lookup through a dynamic module.
if (mpath[0] == '/')
enable_vma_tracker (*this);
... because we already have pragma:vma, and I believe my suggestion addresses
the variable lookup. I think this will also make it so the @var patch doesn't
need to manually enable_vma_tracker(), since dwflpp can enable it as needed.
Another way to handle this is to let dwflpp::emit_address() just insert a
pragma:vma in the generated code. This will allow the optimizer a chance to
remove unused references before the vma is actually enabled. We can hopefully
get to a state where the only place calling enable_vma_tracker() is
embeddedcode_info::visit_embeddedcode(), based on pragma:vma.
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* [Bug translator/15688] Accessing globals in DSO or PIE results in read faults
2013-06-27 2:02 [Bug translator/15688] New: Accessing globals in DSO or PIE results in read faults agentzh at gmail dot com
` (2 preceding siblings ...)
2013-06-27 22:17 ` jistone at redhat dot com
@ 2013-06-27 22:51 ` jistone at redhat dot com
3 siblings, 0 replies; 5+ messages in thread
From: jistone at redhat dot com @ 2013-06-27 22:51 UTC (permalink / raw)
To: systemtap
http://sourceware.org/bugzilla/show_bug.cgi?id=15688
Josh Stone <jistone at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|systemtap at sourceware dot org |jistone at redhat dot com
--- Comment #4 from Josh Stone <jistone at redhat dot com> ---
Created attachment 7099
--> http://sourceware.org/bugzilla/attachment.cgi?id=7099&action=edit
Set pragma:vma when dwflpp uses _stp_umodule_relocate
This patch seems to do the trick. It's based on agentzh's v3 @var patch plus
the addendum he linked in comment #2. I'm running a full installcheck now.
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2013-06-27 2:02 [Bug translator/15688] New: Accessing globals in DSO or PIE results in read faults agentzh at gmail dot com
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2013-06-27 19:37 ` agentzh at gmail dot com
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