From 3bc935d932da3d7e8ff21bb3057276338c4ad497 Mon Sep 17 00:00:00 2001 From: benjaminion Date: Tue, 11 Jul 2017 21:22:38 +0100 Subject: LLL: rewrite alloc to avoid issues with edge cases. --- liblll/CodeFragment.cpp | 28 ++++++++++++++++++++++------ liblll/CompilerState.cpp | 2 ++ 2 files changed, 24 insertions(+), 6 deletions(-) (limited to 'liblll') diff --git a/liblll/CodeFragment.cpp b/liblll/CodeFragment.cpp index 56c1e26a..f637dfb1 100644 --- a/liblll/CodeFragment.cpp +++ b/liblll/CodeFragment.cpp @@ -523,14 +523,30 @@ void CodeFragment::constructOperation(sp::utree const& _t, CompilerState& _s) requireSize(1); requireDeposit(0, 1); - m_asm.append(Instruction::MSIZE); - m_asm.append(u256(0)); + // (alloc N): + // - Evaluates to (msize) before the allocation - the start of the allocated memory + // - Does not allocate memory when N is zero + // - Size of memory allocated is N bytes rounded up to a multiple of 32 + // - Uses MLOAD to expand MSIZE to avoid modifying memory. + + auto end = m_asm.newTag(); + m_asm.append(Instruction::MSIZE); // Result will be original top of memory + m_asm.append(code[0].m_asm, 1); // The alloc argument N + m_asm.append(Instruction::DUP1); + m_asm.append(Instruction::ISZERO);// (alloc 0) does not change MSIZE + m_asm.appendJumpI(end); m_asm.append(u256(1)); - m_asm.append(code[0].m_asm, 1); - m_asm.append(Instruction::MSIZE); + m_asm.append(Instruction::DUP2); // Copy N + m_asm.append(Instruction::SUB); // N-1 + m_asm.append(u256(0x1f)); // Bit mask + m_asm.append(Instruction::NOT); // Invert + m_asm.append(Instruction::AND); // Align N-1 on 32 byte boundary + m_asm.append(Instruction::MSIZE); // MSIZE is cheap m_asm.append(Instruction::ADD); - m_asm.append(Instruction::SUB); - m_asm.append(Instruction::MSTORE8); + m_asm.append(Instruction::MLOAD); // Updates MSIZE + m_asm.append(Instruction::POP); // Discard the result of the MLOAD + m_asm.append(end); + m_asm.append(Instruction::POP); // Discard duplicate N _s.usedAlloc = true; } diff --git a/liblll/CompilerState.cpp b/liblll/CompilerState.cpp index 5d38bb8c..9701e16b 100644 --- a/liblll/CompilerState.cpp +++ b/liblll/CompilerState.cpp @@ -46,6 +46,8 @@ void CompilerState::populateStandard() { static const string s = "{" "(def 'panic () (asm INVALID))" + // Alternative macro version of alloc, which is currently implemented in the parser + // "(def 'alloc (n) (raw (msize) (when n (pop (mload (+ (msize) (& (- n 1) (~ 0x1f))))))))" "(def 'allgas (- (gas) 21))" "(def 'send (to value) (call allgas to value 0 0 0 0))" "(def 'send (gaslimit to value) (call gaslimit to value 0 0 0 0))" -- cgit