CoreCommands,PackageModel: introduce -debug-format option
#6659
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neonichu
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Jun 20, 2023
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This adds a new flag `-debug-format` that allows some structured control over the debug information format. This is particularly important for Windows where there are two different debugging information formats: - Code View (PDB) - DWARF While theoretically LLDB supports PDBs, the overall support for that is limited. Furthermore, the CodeView emitted by the swift frontend is limiting for debugging as expression evaluation as not possible due to the debug information encoding employed by Swift: skeletal information is emitted into the binary and the type information is queried dynamically by the AST deserialiser in the compiler. DWARF on the other hand does not support PE/COFF particularly well (e.g. exceeding the section name limits, representations potentially not being serialisable into the object file, etc), but allows a better experience with LLDB. More importantly, it breaks debugging with the system libraries (e.g. kernel32 or NTDLL). As a result, while it is often used with Swift code, PDBs can also be beneficial. Furthermore, DWARF forces the use of lld as the linker as link does not properly emit linked DWARF information. Provide a top-level control to emit the debug information in a particular format as both of these options require altering the C/C++, Swift, and linker flags. We default to DWARF on all platforms, but on Windows, if CodeView is selected, we will alter the flags appropriately to ease switching of debug information format.
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@swift-ci please smoke test |
MaxDesiatov
approved these changes
Jun 21, 2023
neonichu
approved these changes
Jun 21, 2023
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This adds a new flag
-debug-formatthat allows some structured control over the debug information format. This is particularly important for Windows where there are two different debugging information formats:While theoretically LLDB supports PDBs, the overall support for that is limited. Furthermore, the CodeView emitted by the swift frontend is limiting for debugging as expression evaluation as not possible due to the debug information encoding employed by Swift: skeletal information is emitted into the binary and the type information is queried dynamically by the AST deserialiser in the compiler.
DWARF on the other hand does not support PE/COFF particularly well (e.g. exceeding the section name limits, representations potentially not being serialisable into the object file, etc), but allows a better experience with LLDB. More importantly, it breaks debugging with the system libraries (e.g. kernel32 or NTDLL). As a result, while it is often used with Swift code, PDBs can also be beneficial. Furthermore, DWARF forces the use of lld as the linker as link does not properly emit linked DWARF information.
Provide a top-level control to emit the debug information in a particular format as both of these options require altering the C/C++, Swift, and linker flags. We default to DWARF on all platforms, but on Windows, if CodeView is selected, we will alter the flags appropriately to ease switching of debug information format.