cmd/cgo: use the export'ed details in error messages

[austinderek]

When an unpinned Go pointer (or a pointer to an unpinned Go pointer) is returned from Go to C,

1  package main
2
3  import (
4          "C"
5  )
6
7  //export foo
8  func foo(CLine *C.char) string {
9          return C.GoString(CLine)

10 }
11
12
13 func main() {
14 }

The error message mentions the details of the cgo wrapper,

panic: runtime error: cgo result is unpinned Go pointer or points to unpinned Go pointer

goroutine 17 [running, locked to thread]:
panic({0x798f2341a4c0?, 0xc000112000?})
/usr/lib/go/src/runtime/panic.go:802 +0x168
runtime.cgoCheckArg(0x798f23417e20, 0xc000066e50, 0x0?, 0x0, {0x798f233f5a62, 0x42})
/usr/lib/go/src/runtime/cgocall.go:679 +0x35b
runtime.cgoCheckResult({0x798f23417e20, 0xc000066e50})
/usr/lib/go/src/runtime/cgocall.go:795 +0x4b
_cgoexp_3c910ddb72c4_foo(0x7ffc9fa9bfa0)
_cgo_gotypes.go:65 +0x5d
runtime.cgocallbackg1(0x798f233ec780, 0x7ffc9fa9bfa0, 0x0)
/usr/lib/go/src/runtime/cgocall.go:446 +0x289
runtime.cgocallbackg(0x798f233ec780, 0x7ffc9fa9bfa0, 0x0)
/usr/lib/go/src/runtime/cgocall.go:350 +0x132
runtime.cgocallbackg(0x798f233ec780, 0x7ffc9fa9bfa0, 0x0)
:1 +0x2b
runtime.cgocallback(0x0, 0x0, 0x0)
/usr/lib/go/src/runtime/asm_amd64.s:1082 +0xcd
runtime.goexit({})
/usr/lib/go/src/runtime/asm_amd64.s:1693 +0x1

The cgo wrapper (_cgoexp_3c910ddb72c4_foo) is located in a temporary build artifact (_cgo_gotypes.go)

$ go tool cgo -objdir objdir parse.go
$ cat -n objdir/_cgo_gotypes.go | sed -n '55,70p'
55 //go:cgo_export_dynamic foo
56 //go:linkname _cgoexp_d48770e267d1_foo _cgoexp_d48770e267d1_foo
57 //go:cgo_export_static _cgoexp_d48770e267d1_foo
58 func _cgoexp_d48770e267d1_foo(a *struct {
59 p0 *_Ctype_char
60 r0 string
61 }) {
62 a.r0 = foo(a.p0)
63 _cgoCheckResult(a.r0)
64 }

The details of the export'ed function are expected in the error message.

Use them in error messages.

panic: runtime error: cgo result is unpinned Go pointer or points to unpinned Go pointer

goroutine 17 [running, locked to thread]:
panic({0x7df72b1d8ae0?, 0x3ec8a1790030?})
/mnt/go/src/runtime/panic.go:877 +0x16f
runtime.cgoCheckArg(0x7df72b1d62c0, 0x3ec8a16eee50, 0x68?, 0x0, {0x7df72b1ad44c, 0x42})
/mnt/go/src/runtime/cgocall.go:679 +0x35b
runtime.cgoCheckResult({0x7df72b1d62c0, 0x3ec8a16eee50})
/mnt/go/src/runtime/cgocall.go:795 +0x4b
_cgoexp_3c910ddb72c4_foo(0x7ffca1b21020)
/mnt/tmp/parse.go:8 +0x5d
runtime.cgocallbackg1(0x7df72b1a4360, 0x7ffca1b21020, 0x0)
/mnt/go/src/runtime/cgocall.go:446 +0x289
runtime.cgocallbackg(0x7df72b1a4360, 0x7ffca1b21020, 0x0)
/mnt/go/src/runtime/cgocall.go:350 +0x132
runtime.cgocallbackg(0x7df72b1a4360, 0x7ffca1b21020, 0x0)
:1 +0x2b
runtime.cgocallback(0x0, 0x0, 0x0)
/mnt/go/src/runtime/asm_amd64.s:1101 +0xcd
runtime.goexit({})
/mnt/go/src/runtime/asm_amd64.s:1712 +0x1

Link: https://web.archive.org/web/20251008114504/https://dave.cheney.net/2018/01/08/gos-hidden-pragmas
Suggested-by: Keith Randall [email protected]
For golang#75856

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🔄 This is a mirror of upstream PR golang#76118