* [Bug tapsets/23799] New: sprint_ustack() returns empty strings while sprint_ubacktrace() does not
@ 2018-10-19 18:59 agentzh at gmail dot com
2018-10-19 19:01 ` [Bug tapsets/23799] " agentzh at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: agentzh at gmail dot com @ 2018-10-19 18:59 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=23799
Bug ID: 23799
Summary: sprint_ustack() returns empty strings while
sprint_ubacktrace() does not
Product: systemtap
Version: unspecified
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: tapsets
Assignee: systemtap at sourceware dot org
Reporter: agentzh at gmail dot com
Target Milestone: ---
Consider the following minimal C program:
```
int foo(void) {
return 3;
}
int bar(void) {
return foo();
}
int main(void) {
bar();
return 0;
}
```
Compile and link it like this:
```
gcc -g test.c
```
And then run the following stap oneliner:
```
stap -e 'probe process.function("foo") { printf("{%s}\n{%s}",
sprint_ustack(ubacktrace()), sprint_ubacktrace()); }' -c ./a.out --ldd
```
And the output is
```
{}
{foo+0x4 [a.out]
bar+0x9 [a.out]
main+0x9 [a.out]
__libc_start_main+0xea [libc-2.26.so]
_start+0x2a [a.out]}
```
The weird thing is that `sprint_ustack(ubacktrace())` returns an empty string
while `sprint_ubacktrace()` does not. Why the difference? Is there a bug in
`sprint_ustack()`? Any hints on debugging this thing?
Thanks!
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* [Bug tapsets/23799] sprint_ustack() returns empty strings while sprint_ubacktrace() does not
2018-10-19 18:59 [Bug tapsets/23799] New: sprint_ustack() returns empty strings while sprint_ubacktrace() does not agentzh at gmail dot com
@ 2018-10-19 19:01 ` agentzh at gmail dot com
2018-10-19 21:15 ` agentzh at gmail dot com
2018-10-19 22:12 ` agentzh at gmail dot com
2 siblings, 0 replies; 4+ messages in thread
From: agentzh at gmail dot com @ 2018-10-19 19:01 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=23799
--- Comment #1 from agentzh <agentzh at gmail dot com> ---
Oh, BTW, I'm using the latest stap master on x86_64 (Fedora 26, kernel
4.16.16).
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* [Bug tapsets/23799] sprint_ustack() returns empty strings while sprint_ubacktrace() does not
2018-10-19 18:59 [Bug tapsets/23799] New: sprint_ustack() returns empty strings while sprint_ubacktrace() does not agentzh at gmail dot com
2018-10-19 19:01 ` [Bug tapsets/23799] " agentzh at gmail dot com
@ 2018-10-19 21:15 ` agentzh at gmail dot com
2018-10-19 22:12 ` agentzh at gmail dot com
2 siblings, 0 replies; 4+ messages in thread
From: agentzh at gmail dot com @ 2018-10-19 21:15 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=23799
--- Comment #2 from agentzh <agentzh at gmail dot com> ---
Using `print_ustack(ubacktrace())` works:
```
$ stap -e 'probe process.function("foo") { print_ustack(ubacktrace()); }' -c
./a.out --ldd
0x40048b : foo+0x4/0xb [/mnt/home/agentzh/git/ylang/a.out]
0x40049b : bar+0x9/0xb [/mnt/home/agentzh/git/ylang/a.out]
0x4004a6 : main+0x9/0x13 [/mnt/home/agentzh/git/ylang/a.out]
0x7f3e87d0ffea : __libc_start_main+0xea/0x1c0 [/usr/lib64/libc-2.26.so]
0x4003da : _start+0x2a/0x30 [/mnt/home/agentzh/git/ylang/a.out]
```
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* [Bug tapsets/23799] sprint_ustack() returns empty strings while sprint_ubacktrace() does not
2018-10-19 18:59 [Bug tapsets/23799] New: sprint_ustack() returns empty strings while sprint_ubacktrace() does not agentzh at gmail dot com
2018-10-19 19:01 ` [Bug tapsets/23799] " agentzh at gmail dot com
2018-10-19 21:15 ` agentzh at gmail dot com
@ 2018-10-19 22:12 ` agentzh at gmail dot com
2 siblings, 0 replies; 4+ messages in thread
From: agentzh at gmail dot com @ 2018-10-19 22:12 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=23799
agentzh <agentzh at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |FIXED
--- Comment #3 from agentzh <agentzh at gmail dot com> ---
Committed a fix to master already.
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2018-10-19 18:59 [Bug tapsets/23799] New: sprint_ustack() returns empty strings while sprint_ubacktrace() does not agentzh at gmail dot com
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