Incorrect stack tracing of morestack_noctx function on linux/arm64

[erifan]

1, What version of Delve are you using (dlv version)?
Delve Debugger
Version: 1.9.1
Build: $Id: d81b9fd12bfa603f3cf7a4bc842398bd61c42940 $

2, What version of Go are you using? (go version)?
go version devel go1.20-75cdd2c75d Wed Aug 24 02:54:32 2022 +0000 linux/arm64

3, What operating system and processor architecture are you using?
linux arm64, kernel version: 5.15.52-051552-generic-64k

4, What did you do?
$ cat main.go

`package main

import(
"fmt"
)

func foo(a, b string) string {
var arr [10000]string
for i := 0; i < 10000; i++ {
arr[i] = a + b
}
return arr[90]
}

func main() {
s := ""
for i := 0; i < 1000; i++ {
s += foo("a", "b")
}
fmt.Println(s)
}
`

$ go build -o main main.go
$ dlv exec ./main
$ b morestack_noctxt
$ c
$ bt

5, What did you expect to see?
Normal stack tracing info

6, What did you see instead?
0 0x0000000000069d10 in runtime.morestack_noctxt
at ./go-master/src/runtime/asm_arm64.s:323
1 0x0000000000058ff0 in runtime.concatstring2
at :0
2 0x0000000000058ff0 in runtime.concatstring2
at :0
3 0x0000000000058ff0 in runtime.concatstring2
at :0
4 0x0000000000058ff0 in runtime.concatstring2
at :0
5 0x0000000000058ff0 in runtime.concatstring2
at :0
6 0x0000000000058ff0 in runtime.concatstring2
at :0
7 0x0000000000058ff0 in runtime.concatstring2
at :0
8 0x0000000000058ff0 in runtime.concatstring2
at :0
9 0x0000000000058ff0 in runtime.concatstring2
at :0
10 0x0000000000058ff0 in runtime.concatstring2
at :0
11 0x0000000000058ff0 in runtime.concatstring2
at :0
12 0x0000000000058ff0 in runtime.concatstring2
at :0
13 0x0000000000058ff0 in runtime.concatstring2
at :0
14 0x0000000000058ff0 in runtime.concatstring2
at :0
Sending output to pager...
0 0x0000000000069d10 in runtime.morestack_noctxt
at ./go-master/src/runtime/asm_arm64.s:323
1 0x0000000000058ff0 in runtime.concatstring2
at :0
2 0x0000000000058ff0 in runtime.concatstring2
at :0
3 0x0000000000058ff0 in runtime.concatstring2
at :0
4 0x0000000000058ff0 in runtime.concatstring2
at :0
5 0x0000000000058ff0 in runtime.concatstring2
at :0
6 0x0000000000058ff0 in runtime.concatstring2
at :0
7 0x0000000000058ff0 in runtime.concatstring2
at :0
8 0x0000000000058ff0 in runtime.concatstring2
at :0
9 0x0000000000058ff0 in runtime.concatstring2
at :0
10 0x0000000000058ff0 in runtime.concatstring2
at :0
11 0x0000000000058ff0 in runtime.concatstring2
at :0

[aarzilli]

I don't think we should fix this. It is related to golang/go#54332 which is caused by the compiler emitting bad unwind information for that function. Adding a workaround specifically for runtime.morestack_noctxt to delve is easy but you will have the same problem for runtime.morestack only much more complicated because that function actually performs a stack switch.

In general all functions that perform a stack switch have places where stacktraces end up being wrong. The format of debug_frame is very flexible so in theory it would be possible to fix this but it would involve a lot of effort and it would have to be done in the compiler, not as a series of workarounds in the debugger.

Thus, I'm closing this as "won't fix". However if you believe that this function in particular deserves a workaround more than any other function that suffers from the same problem, please explain why and I will reconsider.