22 lines
1.4 KiB
Plaintext
22 lines
1.4 KiB
Plaintext
offsetof is resolved very early in gcc, only INTEGER_CST is left but no type information in gimple
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-> define __builtin_offsetof as __spslr_offsetof("type", "member", __builtin_offsetof(type, member))
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-> gcc does not know what to do with __spslr_offsetof so it remains in tree during gimple
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-> plugin can extract type and member name and then replace the call with just the INTEGER_CST
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precise per-instruction labels are required at RTL level
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single gimple statement can cause multiple RTL instructions
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only out-of-the-box mapping is location (line, file, ...)
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multiple gimple statements can share single location
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gimple optimizations can merge statements from different locations
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-> build logic tree at gimple but after gimple optimizations (right before conversion to RTL)
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-> at RTL, pattern match sets of RTL instructions with same location to pattern of gimple statements
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-> attach notes to any RTL instruction that accesses relevant structs
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-> notes are propagated throughout RTL optimizations
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-> at the very end of RTL handling, discover notes and add assembly labels
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Constant foldable expressions, e.g. "size_t myOffset = ((size_t)&((struct task_struct*)0)->tasks);", are invisible
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-> gcc folds those expressions before PLUGIN_FINISH_PARSE_FUNCTION
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-> any recoverability of COMPONENT_REF is impossible
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-> requires gcc patch (fairly small one though)
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-> fold_offsetof in the C frontend is responsible
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