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* [Bug c++/29918] New: GDB cannot step or break into template functions compiled with g++ -Og
@ 2022-12-19 6:27 vimacs.hacks at gmail dot com
2022-12-19 6:28 ` [Bug c++/29918] " vimacs.hacks at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: vimacs.hacks at gmail dot com @ 2022-12-19 6:27 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=29918
Bug ID: 29918
Summary: GDB cannot step or break into template functions
compiled with g++ -Og
Product: gdb
Version: 12.1
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
Assignee: unassigned at sourceware dot org
Reporter: vimacs.hacks at gmail dot com
Target Milestone: ---
This is another issue posted on
https://sourceware.org/pipermail/gdb/2022-November/050431.html
For the following C++ code, I find that GDB (both 12.1 and
gdb-13-branchpoint-5-g2a517ca94d3) cannot step or break into C++ template
function t0<int> compiled with g++ -Og (GCC version 12.2.0), while LLDB from
LLVM 14.0.6 can step into this function:
template <typename T = int>
int t0(int n)
{
int sum = 0;
for (int i = 0; i < n; ++i) {
sum += i * i;
}
return sum;
}
int t1(int n)
{
int sum = 0;
for (int i = 0; i < n; ++i) {
sum += i * i;
}
return sum;
}
int main()
{
int a = t0(5);
int b = t1(5);
return a + b;
}
The behavior in GDB looks like this:
Breakpoint 1, main () at template_func.cc:21
21 {
(gdb) n
22 int a = t0(5);
(gdb) s
t0<int> (n=n@entry=5) at template_func.cc:2
2 int t0(int n)
(gdb)
main () at template_func.cc:23
23 int b = t1(5);
(gdb)
The assembly output of "g++-g -Og" and "g++ -g -O0" are both attached in the
attachment of the following comments, which can be assembled and reproduce this
issue.
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* [Bug c++/29918] GDB cannot step or break into template functions compiled with g++ -Og
2022-12-19 6:27 [Bug c++/29918] New: GDB cannot step or break into template functions compiled with g++ -Og vimacs.hacks at gmail dot com
@ 2022-12-19 6:28 ` vimacs.hacks at gmail dot com
2022-12-19 6:28 ` vimacs.hacks at gmail dot com
2022-12-19 16:30 ` tromey at sourceware dot org
2 siblings, 0 replies; 4+ messages in thread
From: vimacs.hacks at gmail dot com @ 2022-12-19 6:28 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=29918
--- Comment #1 from vimacs.hacks at gmail dot com <vimacs.hacks at gmail dot com> ---
Created attachment 14523
--> https://sourceware.org/bugzilla/attachment.cgi?id=14523&action=edit
Assembly output with -g -O0
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* [Bug c++/29918] GDB cannot step or break into template functions compiled with g++ -Og
2022-12-19 6:27 [Bug c++/29918] New: GDB cannot step or break into template functions compiled with g++ -Og vimacs.hacks at gmail dot com
2022-12-19 6:28 ` [Bug c++/29918] " vimacs.hacks at gmail dot com
@ 2022-12-19 6:28 ` vimacs.hacks at gmail dot com
2022-12-19 16:30 ` tromey at sourceware dot org
2 siblings, 0 replies; 4+ messages in thread
From: vimacs.hacks at gmail dot com @ 2022-12-19 6:28 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=29918
--- Comment #2 from vimacs.hacks at gmail dot com <vimacs.hacks at gmail dot com> ---
Created attachment 14524
--> https://sourceware.org/bugzilla/attachment.cgi?id=14524&action=edit
Assembly output with -g -Og
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^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/29918] GDB cannot step or break into template functions compiled with g++ -Og
2022-12-19 6:27 [Bug c++/29918] New: GDB cannot step or break into template functions compiled with g++ -Og vimacs.hacks at gmail dot com
2022-12-19 6:28 ` [Bug c++/29918] " vimacs.hacks at gmail dot com
2022-12-19 6:28 ` vimacs.hacks at gmail dot com
@ 2022-12-19 16:30 ` tromey at sourceware dot org
2 siblings, 0 replies; 4+ messages in thread
From: tromey at sourceware dot org @ 2022-12-19 16:30 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=29918
Tom Tromey <tromey at sourceware dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
CC| |tromey at sourceware dot org
Last reconfirmed| |2022-12-19
Status|UNCONFIRMED |NEW
--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
I was able to reproduce with the Fedora 36 system gcc.
However, the line table that is emitted is weird.
First, consider the line table for lines 12-18. This
corresponds to the function t1:
File name Line number Starting address View
Stmt
prog.cc 12 0x400576
x
prog.cc 13 0x400576 1
x
prog.cc 14 0x400576 2
x
prog.cc 14 0x400576 3
prog.cc 13 0x40057b
prog.cc 14 0x400580
prog.cc 15 0x400582
x
prog.cc 15 0x400582 1
prog.cc 15 0x400587
prog.cc 14 0x400589
x
prog.cc 14 0x40058c
x
prog.cc 17 0x400590
x
prog.cc 18 0x400590 1
prog.cc 18 0x400592
Not that many lines are represented and multiple lines in this range have the
statement marker.
Now consider the line table for lines 2-9, aka t0<>:
File name Line number Starting address View
Stmt
prog.cc 2 0x4005ae
x
prog.cc 5 0x4005ae 1
prog.cc 4 0x4005b3
prog.cc 5 0x4005b8
prog.cc 6 0x4005ba
prog.cc 6 0x4005bf
prog.cc 5 0x4005c1
x
prog.cc 5 0x4005c4
x
prog.cc 9 0x4005c8
prog.cc 9 0x4005ca
This seems weird.
Perhaps gdb can work around it, after all lldb does.
I tend to suspect one of the line table patches that went in in the 12 era,
though I haven't tried bisecting or anything.
Anyway, while I agree gdb can be better, I think there's also a compiler bug.
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2022-12-19 6:27 [Bug c++/29918] New: GDB cannot step or break into template functions compiled with g++ -Og vimacs.hacks at gmail dot com
2022-12-19 6:28 ` [Bug c++/29918] " vimacs.hacks at gmail dot com
2022-12-19 6:28 ` vimacs.hacks at gmail dot com
2022-12-19 16:30 ` tromey at sourceware dot org
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