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cmd/cgo: add note about bug writing C pointers to uninitialized C memory

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Describe the problem as a bug, since it is not implied by the rest of
the pointer passing rules, and it may be possible to fix it.

Updates #19928

Change-Id: I2d336e7336b2a215c0b8cf909a203201ef1b054e
Reviewed-on: https://go-review.googlesource.com/123658
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Ian Lance Taylor 2018-07-12 11:57:05 -07:00
parent b323709a5c
commit 1177b089f5
1 changed files with 8 additions and 0 deletions
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8
src/cmd/cgo/doc.go
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@ -377,6 +377,14 @@ and of course there is nothing stopping the C code from doing anything
it likes. However, programs that break these rules are likely to fail
in unexpected and unpredictable ways.
Note: the current implementation has a bug. While Go code is permitted
to write nil or a C pointer (but not a Go pointer) to C memory, the
current implementation may sometimes cause a runtime error if the
contents of the C memory appear to be a Go pointer. Therefore, avoid
passing uninitialized C memory to Go code if the Go code is going to
store pointer values in it. Zero out the memory in C before passing it
to Go.
Special cases
A few special C types which would normally be represented by a pointer