Writeup

writeup.txt

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+offsetof is resolved very early in gcc, only INTEGER_CST is left but no type information in gimple
+	-> define __builtin_offsetof as __spslr_offsetof("type", "member", __builtin_offsetof(type, member))
+	-> gcc does not know what to do with __spslr_offsetof so it remains in tree during gimple
+	-> plugin can extract type and member name and then replace the call with just the INTEGER_CST
+
+precise per-instruction labels are required at RTL level
+	single gimple statement can cause multiple RTL instructions
+	only out-of-the-box mapping is location (line, file, ...)
+	multiple gimple statements can share single location
+	gimple optimizations can merge statements from different locations
+	-> build logic tree at gimple but after gimple optimizations (right before conversion to RTL)
+	-> at RTL, pattern match sets of RTL instructions with same location to pattern of gimple statements
+	-> attach notes to any RTL instruction that accesses relevant structs
+	-> notes are propagated throughout RTL optimizations
+	-> at the very end of RTL handling, discover notes and add assembly labels