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cmd/cgo: [1][2][3][0]byte doesn't work on OS X Lion #8611
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Looking at that _cgo_.o file with llvm-dwarfdump-3.5, it looks like this field: char y[3][0][1][2]; is generating this DW_TAG_array_type entry: 0x00000193: DW_TAG_array_type [4] * DW_AT_sibling [DW_FORM_ref4] (cu + 0x01b5 => {0x000001b5}) DW_AT_type [DW_FORM_ref4] (cu + 0x00c0 => {0x000000c0}) 0x0000019c: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x008b => {0x0000008b}) DW_AT_upper_bound [DW_FORM_data1] (0x02) 0x000001a2: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x008b => {0x0000008b}) DW_AT_upper_bound [DW_FORM_data1] (0x00) 0x000001a8: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x008b => {0x0000008b}) DW_AT_upper_bound [DW_FORM_data1] (0x00) 0x000001ae: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x008b => {0x0000008b}) DW_AT_upper_bound [DW_FORM_data1] (0x01) Whereas GCC 4.8.2 and Clang 3.5 generate this: 0x000000aa: DW_TAG_array_type [4] * DW_AT_type [DW_FORM_ref4] (cu + 0x0082 => {0x00000082}) DW_AT_sibling [DW_FORM_ref4] (cu + 0x00cb => {0x000000cb}) 0x000000b3: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x007b => {0x0000007b}) DW_AT_upper_bound [DW_FORM_data1] (0x02) 0x000000b9: DW_TAG_subrange_type [6] DW_AT_type [DW_FORM_ref4] (cu + 0x007b => {0x0000007b}) 0x000000be: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x007b => {0x0000007b}) DW_AT_upper_bound [DW_FORM_data1] (0x00) 0x000000c4: DW_TAG_subrange_type [5] DW_AT_type [DW_FORM_ref4] (cu + 0x007b => {0x0000007b}) DW_AT_upper_bound [DW_FORM_data1] (0x01) I.e., for the [0] sized entry, they omit the DW_AT_upper_bound entry. Looking quickly through LLVM commit history, it seems like this commit on Dec 2012 was probably when they fixed this behavior: http://llvm.org/viewvc/llvm-project?view=revision&revision=169312 It looks like Clang 3.3 was the first release to include that fix. So presumably this test will be broken on any version of OS X that uses an older (i.e., buggy) version of Clang, such as Lion. |
I don't think there's anything we can do to truly solve this problem when the compiler generates bad DWARF type information. E.g., from the Clang 3.0 _cgo_.o, we can't distinguish whether the field should have type "[3][0][1][2]C.char" or "[3][1][0][2]C.char". Arguably either would be better than "[0][1][1][2]C.char", but I don't think it makes sense to further complicate debug/dwarf if we can't guarantee a correct answer. I suspect the best solution unfortunately is to simply disable misc/cgo/test/issue8428.go on older OS X with buggy versions of Clang. According to http://stackoverflow.com/questions/8674546/how-to-update-llvm-clang-on-mac-osx, that seems to be OS X Lion (Clang 3.0) and OS X Mountain Lion (Clang 3.2). Is it possible to use +build rules to skip particular versions of a platform? Or should I just skip all of darwin for issue8428.go? |
CL https://golang.org/cl/135990043 mentions this issue. |
This issue was closed by revision f2e7fa9. Status changed to Fixed. |
wheatman
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Jun 25, 2018
Clang 3.2 and older (as shipped with OS X Mountain Lion and older) outputs ambiguous DWARF debug info that makes it impossible for us to reconstruct accurate type information as required for this test. Fixes golang#8611. LGTM=rsc R=r, rsc, minux CC=golang-codereviews https://golang.org/cl/135990043
wheatman
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Jul 9, 2018
Clang 3.2 and older (as shipped with OS X Mountain Lion and older) outputs ambiguous DWARF debug info that makes it impossible for us to reconstruct accurate type information as required for this test. Fixes golang#8611. LGTM=rsc R=r, rsc, minux CC=golang-codereviews https://golang.org/cl/135990043
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