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cmd/cgo: use the export'ed details in error messages #76118

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@ariel-anieli ariel-anieli commented Oct 30, 2025 •
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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)
        <autogenerated>: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)
        <autogenerated>: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 #75856

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This PR (HEAD: 956aa4b) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/716441.

Important tips:

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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Message from Ariel Otilibili Anieli:

Patch Set 1:

(2 comments)

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

@austinderek austinderek mentioned this pull request Oct 30, 2025
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Message from t hepudds:

Patch Set 1: Commit-Queue+1

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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Message from Go LUCI:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2025-10-30T13:06:19Z","revision":"5eb0a3d78893485106a8837e76486d73857acc9d"}

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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Message from t hepudds:

Patch Set 1: -Commit-Queue

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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Message from Go LUCI:

Patch Set 1:

This CL has passed the run

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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Message from Go LUCI:

Patch Set 1: LUCI-TryBot-Result+1

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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Message from t hepudds:

Patch Set 1:

(1 comment)

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

@ariel-anieli
cmd/cgo: use the export'ed details in error messages
eb376d9 
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)
            <autogenerated>: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)
            <autogenerated>: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
@ariel-anieli ariel-anieli force-pushed the cgo-export-orig-func-name branch from 956aa4b to eb376d9 Compare October 30, 2025 14:39
@gopherbot
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This PR (HEAD: eb376d9) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/716441.

Important tips:

  • Don't comment on this PR. All discussion takes place in Gerrit.
  • You need a Gmail or other Google account to log in to Gerrit.
  • To change your code in response to feedback:
    • Push a new commit to the branch used by your GitHub PR.
    • A new "patch set" will then appear in Gerrit.
    • Respond to each comment by marking as Done in Gerrit if implemented as suggested. You can alternatively write a reply.
    • Critical: you must click the blue Reply button near the top to publish your Gerrit responses.
    • Multiple commits in the PR will be squashed by GerritBot.
  • The title and description of the GitHub PR are used to construct the final commit message.
    • Edit these as needed via the GitHub web interface (not via Gerrit or git).
    • You should word wrap the PR description at ~76 characters unless you need longer lines (e.g., for tables or URLs).
  • See the Sending a change via GitHub and Reviews sections of the Contribution Guide as well as the FAQ for details.

@gopherbot
Copy link
Contributor

Message from Ariel Otilibili Anieli:

Patch Set 1:

(2 comments)

Please don’t reply on this GitHub thread. Visit golang.org/cl/716441.
After addressing review feedback, remember to publish your drafts!

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