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LLL: alloc issues round-up #2545

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Merged
axic merged 1 commit into from
Jul 11, 2017
Merged

LLL: alloc issues round-up #2545

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28 changes: 22 additions & 6 deletions liblll/CodeFragment.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -523,14 +523,30 @@ void CodeFragment::constructOperation(sp::utree const& _t, CompilerState& _s)
requireSize(1);
requireDeposit(0, 1);

m_asm.append(Instruction::MSIZE);
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@axic axic Jul 11, 2017

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Please add a comment here explaining the rules:

  • returns msize prior to expansion
  • doesn't allocate in case of N = 0
  • rounds N to a multiple of 32
  • uses MLOAD to expand, which keeps memory untouched

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@benjaminion benjaminion Jul 11, 2017

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Done.

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;
}
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2 changes: 2 additions & 0 deletions liblll/CompilerState.cpp
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Expand Up @@ -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))"
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55 changes: 55 additions & 0 deletions test/liblll/EndToEndTest.cpp
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Expand Up @@ -467,6 +467,61 @@ BOOST_AUTO_TEST_CASE(send_three_args)
BOOST_CHECK(balanceAt(Address(0xdead)) == 42);
}

// Regression test for edge case that previously failed
BOOST_AUTO_TEST_CASE(alloc_zero)
{
char const* sourceCode = R"(
(returnlll
(seq
(mstore 0x00 (~ 0))
(alloc 0)
(return 0x00 0x20)))
)";
compileAndRun(sourceCode);
BOOST_CHECK(callFallback() == encodeArgs(u256(-1)));
}

BOOST_AUTO_TEST_CASE(alloc_size)
{
char const* sourceCode = R"(
(returnlll
(seq
(mstore 0x00 0) ; reserve space for the result of the alloc
(mstore 0x00 (alloc (calldataload 0x04)))
(return (- (msize) (mload 0x00)))))
)";
compileAndRun(sourceCode);
BOOST_CHECK(callContractFunction("test()", 0) == encodeArgs(u256(0)));
BOOST_CHECK(callContractFunction("test()", 1) == encodeArgs(u256(32)));
BOOST_CHECK(callContractFunction("test()", 32) == encodeArgs(u256(32)));
BOOST_CHECK(callContractFunction("test()", 33) == encodeArgs(u256(64)));
}

BOOST_AUTO_TEST_CASE(alloc_start)
{
char const* sourceCode = R"(
(returnlll
(seq
(mstore 0x40 0) ; Set initial MSIZE to 0x60
(return (alloc 1))))
)";
compileAndRun(sourceCode);
BOOST_CHECK(callFallback() == encodeArgs(96));
}

BOOST_AUTO_TEST_CASE(alloc_with_variable)
{
char const* sourceCode = R"(
(returnlll
(seq
(set 'x (alloc 1))
(mstore8 @x 42) ; ASCII '*'
(return @x 0x20)))
)";
compileAndRun(sourceCode);
BOOST_CHECK(callFallback() == encodeArgs("*"));
}

BOOST_AUTO_TEST_CASE(msg_six_args)
{
char const* sourceCode = R"(
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