From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?q?Christophe_B=C3=A9dard_via_lttng-dev?=
 <lttng-dev@lists.lttng.org>
Subject: Re: Correctly using callstack-user context
Date: Wed, 13 May 2020 09:42:42 -0400
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To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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On Tue, 12 May 2020 at 08:27, Mathieu Desnoyers <
mathieu.desnoyers@efficios.com> wrote:

> How does your test program issue the system call ? Is it directly with
> syscall() (see syscall(2) man page), or
> does it call into libc ? Is your entire libc compiled with
> -fno-omit-frame-pointer ?
>

Indirectly, through libc/libstdc++. We use the default system libs (which I
assume use -O, which in turn implies -fomit-frame-pointer).


> As soon as one library in the chain to the system call is compiled without
> frame pointers, this is where the
> stack walk stops. This is usually libc.
>

I see. Thanks for the information. Not sure we want to ship a custom libc
unfortunately.

Related question: how feasible would adding the callstack-user context to
userspace events be? If it is feasible, is such a feature planned?



Christophe

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><div class=3D"gmail_quote"><div=
 dir=3D"ltr" class=3D"gmail_attr">On Tue, 12 May 2020 at 08:27, Mathieu Des=
noyers &lt;<a href=3D"mailto:mathieu.desnoyers@efficios.com" target=3D"_bla=
nk">mathieu.desnoyers@efficios.com</a>&gt; wrote:</div><blockquote class=3D=
"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(2=
04,204,204);padding-left:1ex"><div><div style=3D"font-family:arial,helvetic=
a,sans-serif;font-size:12pt;color:rgb(0,0,0)"><div><div>How does your test =
program issue the system call ? Is it directly with syscall() (see syscall(=
2) man page), or<br></div><div>does it call into libc ? Is your entire libc=
 compiled with -fno-omit-frame-pointer ?</div></div></div></div></blockquot=
e><div><br></div><div>Indirectly, through libc/libstdc++. We use the defaul=
t system libs (which I assume use -O, which in turn implies -fomit-frame-po=
inter).</div><div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:=
1ex"><div style=3D"font-family:arial,helvetica,sans-serif;font-size:12pt;co=
lor:rgb(0,0,0)"><div></div><div>As soon as one library in the chain to the =
system call is compiled without frame pointers, this is where the<br></div>=
<div>stack walk stops. This is usually libc.</div></div></blockquote><div><=
br></div><div>I see. Thanks for the information. Not sure we want to ship a=
 custom libc unfortunately.</div><div><br></div><div>Related question: how =
feasible would adding the callstack-user context to userspace=C2=A0events b=
e? If it is feasible, is such a feature planned?</div><div><br></div><div><=
br></div><div><br></div><div>Christophe=C2=A0</div></div></div>

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Date: Wed, 13 May 2020 09:42:42 -0400
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To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: lttng-dev <lttng-dev@lists.lttng.org>
Subject: Re: [lttng-dev] Correctly using callstack-user context
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On Tue, 12 May 2020 at 08:27, Mathieu Desnoyers <
mathieu.desnoyers@efficios.com> wrote:

> How does your test program issue the system call ? Is it directly with
> syscall() (see syscall(2) man page), or
> does it call into libc ? Is your entire libc compiled with
> -fno-omit-frame-pointer ?
>

Indirectly, through libc/libstdc++. We use the default system libs (which I
assume use -O, which in turn implies -fomit-frame-pointer).


> As soon as one library in the chain to the system call is compiled without
> frame pointers, this is where the
> stack walk stops. This is usually libc.
>

I see. Thanks for the information. Not sure we want to ship a custom libc
unfortunately.

Related question: how feasible would adding the callstack-user context to
userspace events be? If it is feasible, is such a feature planned?



Christophe

--0000000000004058e905a587c316
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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><div class=3D"gmail_quote"><div=
 dir=3D"ltr" class=3D"gmail_attr">On Tue, 12 May 2020 at 08:27, Mathieu Des=
noyers &lt;<a href=3D"mailto:mathieu.desnoyers@efficios.com" target=3D"_bla=
nk">mathieu.desnoyers@efficios.com</a>&gt; wrote:</div><blockquote class=3D=
"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(2=
04,204,204);padding-left:1ex"><div><div style=3D"font-family:arial,helvetic=
a,sans-serif;font-size:12pt;color:rgb(0,0,0)"><div><div>How does your test =
program issue the system call ? Is it directly with syscall() (see syscall(=
2) man page), or<br></div><div>does it call into libc ? Is your entire libc=
 compiled with -fno-omit-frame-pointer ?</div></div></div></div></blockquot=
e><div><br></div><div>Indirectly, through libc/libstdc++. We use the defaul=
t system libs (which I assume use -O, which in turn implies -fomit-frame-po=
inter).</div><div>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:=
1ex"><div style=3D"font-family:arial,helvetica,sans-serif;font-size:12pt;co=
lor:rgb(0,0,0)"><div></div><div>As soon as one library in the chain to the =
system call is compiled without frame pointers, this is where the<br></div>=
<div>stack walk stops. This is usually libc.</div></div></blockquote><div><=
br></div><div>I see. Thanks for the information. Not sure we want to ship a=
 custom libc unfortunately.</div><div><br></div><div>Related question: how =
feasible would adding the callstack-user context to userspace=C2=A0events b=
e? If it is feasible, is such a feature planned?</div><div><br></div><div><=
br></div><div><br></div><div>Christophe=C2=A0</div></div></div>

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