* [Bug translator/18389] New: gcc5 code folding breaks tracepoint queries
@ 2015-05-08 19:49 jistone at redhat dot com
2015-05-08 19:50 ` [Bug translator/18389] " jistone at redhat dot com
0 siblings, 1 reply; 2+ messages in thread
From: jistone at redhat dot com @ 2015-05-08 19:49 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=18389
Bug ID: 18389
Summary: gcc5 code folding breaks tracepoint queries
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: translator
Assignee: systemtap at sourceware dot org
Reporter: jistone at redhat dot com
Target Milestone: ---
GCC5 now has Identical Code Folding, -fipa-icf, and it's enabled by default at
-O2 or higher.
SystemTap's tracepoint queries use stub functions like:
void stapprobe_##name(proto) {}
When multiple tracepoint's proto is the same in a given object, GCC5 is merging
them, so we only find one of them in debuginfo.
For instance, sys_enter takes (struct pt_regs *regs, long id), and sys_exit
takes (struct pt_regs *regs, long reg). These are identical as far as gcc is
concerned, so they're merged. So stap -l 'kernel.trace("sys_*")' only shows me
sys_exit.
The "winner" may not be deterministic, but for now it appears to be the last
one declared. Another example is that there are 8 "ext4_*" tracepoints which
take just (struct inode *inode), and only ext4_load_inode shows up in stap.
Adding -fno-ipa-icf will disable this, if we can do that in a compatible way.
Another possibility is to force uniqueness, perhaps something like:
int stapprobe_##name(proto) {
static int i = 0;
return ++i;
}
(The tracepoint query objects are never linked or executed, so the function
body is irrelevant as long as they all show up in debuginfo.)
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* [Bug translator/18389] gcc5 code folding breaks tracepoint queries
2015-05-08 19:49 [Bug translator/18389] New: gcc5 code folding breaks tracepoint queries jistone at redhat dot com
@ 2015-05-08 19:50 ` jistone at redhat dot com
0 siblings, 0 replies; 2+ messages in thread
From: jistone at redhat dot com @ 2015-05-08 19:50 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=18389
Josh Stone <jistone at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|systemtap at sourceware dot org |jistone at redhat dot com
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