[Lldb-commits] [PATCH] D134041: [LLDB] Enable non-trivial types in EmulateInstruction::Context

[David Spickett via Phabricator via lldb-commits]

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In future I want to extend RegisterInfo and that will likely be non trivial
types like string and vector. RegisterInfo gets stored in Context, so Context
must be changed to a discriminated enum that properly calls destructors.

(which would be std::variant but although llvm is using -std=c++17 I don't
think we can expect c++17 library features just yet)

As so much existing code does this:
Context ctx;
// Lots of code that interacts with ctx...
ctx.Set<...>

I wasn't able to switch to factory functions for the Set<...> methods without a lot
more changes. Instead I've made the default constructor construct to the NoArgs type
and then Set<...> will change the type later.

Whenever you call a Set<...> it will destroy whatever is currently in the union
before setting the new data. Potentially non trivial types like RegisterInfos here are
placement newed because otherwise operator= would try to destroy the existing data
which is in fact uninitialised memory as far as we're concerned.

For the destructor we switch on the current info_type to know what to destruct.
(info_type that was made private in a previous change, so we know we have control of it)

Some places in lldb were using memset to initalise RegisterInfos. I tracked these
down with GCC's -Wclass-memaccess.
https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-Wclass-memaccess

To replace these I've added sensible default values for each member in RegisterInfo
and filled kinds with LLDB_INVALID_REGNUM in the default constructor.

Depends on D134039 <https://reviews.llvm.org/D134039>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D134041

Files:
  lldb/include/lldb/Core/EmulateInstruction.h
  lldb/include/lldb/lldb-private-types.h
  lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
  lldb/source/Plugins/Instruction/MIPS/EmulateInstructionMIPS.cpp
  lldb/source/Plugins/Instruction/MIPS/EmulateInstructionMIPS.h
  lldb/source/Plugins/Instruction/MIPS64/EmulateInstructionMIPS64.cpp
  lldb/source/Plugins/Instruction/MIPS64/EmulateInstructionMIPS64.h
  lldb/source/Target/DynamicRegisterInfo.cpp

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