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runtime/cgo: improve error messages after pointer panic #75894
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This PR (HEAD: 74f2fb0) has been imported to Gerrit for code review. Please visit Gerrit at https://go-review.googlesource.com/c/go/+/711801. Important tips:
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pt is defined in range, then re-assigned to itself. Remove it. For golang#75856
The description is misleading: cgoCheckArg is called by both cgoCheckPointer and cgoCheckResult. fix by mentioning cgoCheckResult in the cgoCheckArg description. As well, remove extra spaces between words. For golang#75856
This commit 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 formats an error message with the caller name) - update the cgo pointer tests. 1. cgoCheckResult When an unpinned Go pointer (or a pointer to an unpinned Go pointer) is returned from Go to C, > package main > > import ( > "C" > ) > > //export foo > func foo() map[int]int { > return map[int]int{0: 1,} > } This error shows up at runtime: > panic: runtime error: cgo result is unpinned Go pointer or points to unpinned Go pointer > > goroutine 17 [running, locked to thread]: > panic({0x78ac36001d40?, 0xc000194000?}) > /usr/lib/go/src/runtime/panic.go:802 +0x168 > runtime.cgoCheckArg(0x78ac36002f40, 0xc000190000, 0xd8?, 0x0, {0x78ac35fdda62, 0x42}) > /usr/lib/go/src/runtime/cgocall.go:628 +0x4c5 > runtime.cgoCheckResult({0x78ac36002f40, 0xc000190000}) > /usr/lib/go/src/runtime/cgocall.go:795 +0x4b > _cgoexp_1c29bd2c0b96_foo(0x7fffc16d87b0) > _cgo_gotypes.go:46 +0x6f > runtime.cgocallbackg1(0x78ac35fd4d20, 0x7fffc16d87b0, 0x0) > /usr/lib/go/src/runtime/cgocall.go:446 +0x289 > runtime.cgocallbackg(0x78ac35fd4d20, 0x7fffc16d87b0, 0x0) > /usr/lib/go/src/runtime/cgocall.go:350 +0x132 > runtime.cgocallbackg(0x78ac35fd4d20, 0x7fffc16d87b0, 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 _cgoexp_1c29bd2c0b96_foo is the faulty caller; it is not obvious to find it in the stack trace. Moreover the error does say which kind of pointer caused the panic; for instance, a Go map. Retrieve caller name and pointer kind; use them in the error message: > panic: runtime error: result of cgo function foo is unpinned Go map or points to unpinned Go map > > goroutine 17 [running, locked to thread]: > panic({0x76f2fd69b3c0?, 0x1fba8c79c000?}) > /mnt/go/src/runtime/panic.go:877 +0x16f > runtime.cgoCheckArg(0x76f2fd69c5c0, 0x1fba8c790000, 0x0?, 0x0, 0x1) > /mnt/go/src/runtime/cgocall.go:631 +0x499 > runtime.cgoCheckResult({0x76f2fd69c5c0, 0x1fba8c790000}) > /mnt/go/src/runtime/cgocall.go:798 +0x45 > _cgoexp_1c29bd2c0b96_foo(0x7ffd0803b8c0) > _cgo_gotypes.go:46 +0x6f > runtime.cgocallbackg1(0x76f2fd667680, 0x7ffd0803b8c0, 0x0) > /mnt/go/src/runtime/cgocall.go:446 +0x289 > runtime.cgocallbackg(0x76f2fd667680, 0x7ffd0803b8c0, 0x0) > /mnt/go/src/runtime/cgocall.go:350 +0x132 > runtime.cgocallbackg(0x76f2fd667680, 0x7ffd0803b8c0, 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 2. cgoCheckPointer When an unpinned Go pointer (or a pointer to an unpinned Go pointer) is passed to a C function, > package main > > /* > #include <stdio.h> > void foo(void *bar) {} > */ > import "C" > import "unsafe" > > func main() { > m := map[int]int{0: 1,} > C.foo(unsafe.Pointer(&m)) > } 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/chexit/cgomap.go:12 > main.main() > /mnt/chexit/cgomap.go:12 +0x91 > exit status 2 Retrieve callee name and pointer kind; use them in the error message. > panic: runtime error: cgo argument of function main.main.func1 has Go pointer to unpinned Go map > > goroutine 1 [running]: > main.main.func1(...) > /mnt/chexit/cgomap.go:12 > main.main() > /mnt/chexit/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 golang#75856
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Hello maintainers,
This patchset contains two commits:
The first commit fixes the description of cgoCheckArg.
The second 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:
An unpinned Go pointer refers to a memory location that might be moved or freed by the garbage collector.
Therefore:
cc @ianlancetaylor, @randall77, @seankhliao
Fixes #75856