runtime/cgo: improve error messages after pointer panic

runtime/cgo: improve error messages after pointer panic

This CL improves the error messages after panics due to the
sharing of an unpinned Go pointer (or a pointer to an unpinned Go
pointer) between Go and C.

This occurs when it is:
1. returned from Go to C (through cgoCheckResult)
2. passed as argument to a C function (through cgoCheckPointer).

An unpinned Go pointer refers to a memory location that might be moved or
freed by the garbage collector.

Therefore:

- change the signature of cgoCheckArg (it does the real work behind
  cgoCheckResult and cgoCheckPointer)
- change the signature of cgoCheckUnknownPointer (called by cgoCheckArg
  for checking unexpected pointers)
- introduce cgoFormatErr (it is called by cgoCheckArg and
  cgoCheckUnknownPointer to format panic error messages)
- update the cgo pointer tests (add new tests, and a field errTextRegexp
  to the struct ptrTest)
- remove a loop variable in TestPointerChecks (similar to CL 711640).

1. cgoCheckResult

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

     1  package main
     2
     3  /*
     4     #include <stdio.h>
     5
     6     extern void* GoFoo();
     7
     8     static void CFoo() { GoFoo();}
     9   */
    10  import (
    11          "C"
    12  )
    13
    14  //export GoFoo
    15  func GoFoo() map[int]int {
    16          return map[int]int{0: 1,}
    17  }
    18
    19  func main() {
    20          C.CFoo();
    21  }

This error shows up at runtime:

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

    goroutine 1 [running]:
    main._Cfunc_CFoo()
            _cgo_gotypes.go:46 +0x3a
    main.main()
            /mnt/tmp/parse.go:20 +0xf
    exit status 2

GoFoo is the faulty Go function; it is not mentioned in the error message.

Moreover the error does not say which kind of pointer caused the panic; for
instance, a Go map.

Retrieve name and file/line of the Go function, as well as the kind of
pointer; use them in the error message:

    panic: runtime error: /mnt/tmp/parse.go:15: result of Go function GoFoo called from cgo is unpinned Go map or points to unpinned Go map

    goroutine 1 [running]:
    main._Cfunc_CFoo()
            _cgo_gotypes.go:46 +0x3a
    main.main()
            /mnt/tmp/parse.go:20 +0xf
    exit status 2

2. cgoCheckPointer

When a pointer to an unpinned Go pointer is passed to a C function,

     1  package main
     2
     3  /*
     4  #include <stdio.h>
     5  void foo(void *bar) {}
     6  */
     7  import "C"
     8  import "unsafe"
     9
    10  func main() {
    11          m := map[int]int{0: 1,}
    12          C.foo(unsafe.Pointer(&m))
    13  }

This error shows up at runtime:

    panic: runtime error: cgo argument has Go pointer to unpinned Go pointer

    goroutine 1 [running]:
    main.main.func1(...)
            /mnt/tmp/cgomap.go:12
    main.main()
            /mnt/tmp/cgomap.go:12 +0x91
    exit status 2

Retrieve kind of pointer; use it in the error message.

    panic: runtime error: argument of cgo function has Go pointer to unpinned Go map

    goroutine 1 [running]:
    main.main.func1(...)
            /mnt/tmp/cgomap.go:12
    main.main()
            /mnt/tmp/cgomap.go:12 +0x9b
    exit status 2

Link: https://pkg.go.dev/cmd/cgo#hdr-Passing_pointers
Suggested-by: Ian Lance Taylor <iant@golang.org>
Fixes #75856

Change-Id: Ia72f01df016feeae0cddb2558ced51a1b07e4486
GitHub-Last-Rev: 76257c7dd7c52a3d88234d43ec7f22bda81edcdd
GitHub-Pull-Request: golang/go#75894
Reviewed-on: https://go-review.googlesource.com/c/go/+/711801
Reviewed-by: Funda Secgin <fundasecgin73@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>