diff options
Diffstat (limited to 'packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol')
| -rw-r--r-- | packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol | 68 |
1 files changed, 58 insertions, 10 deletions
diff --git a/packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol b/packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol index 004c3892d..258443bca 100644 --- a/packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol +++ b/packages/contracts/src/2.0.0/protocol/AssetProxy/ERC20Proxy.sol @@ -18,7 +18,6 @@ pragma solidity 0.4.24; -import "../../utils/LibBytes/LibBytes.sol"; import "./MixinAuthorizable.sol"; @@ -59,15 +58,64 @@ contract ERC20Proxy is mstore(96, 0) revert(0, 100) } - - /////// Token contract address /////// - // The token address is found as follows: - // * It is stored at offset 4 in `assetData` contents. - // * This is stored at offset 32 from `assetData`. - // * The offset to `assetData` from Params is stored at offset - // 4 in calldata. - // * The offset of Params in calldata is 4. - // So we read location 4 and add 32 + 4 + 4 to it. + + // `transferFrom`. + // The function is marked `external`, so no abi decodeding is done for + // us. Instead, we expect the `calldata` memory to contain the + // following: + // + // | Area | Offset | Length | Contents | + // |----------|--------|---------|-------------------------------------| + // | Header | 0 | 4 | function selector | + // | Params | | 4 * 32 | function parameters: | + // | | 4 | | 1. offset to assetData (*) | + // | | 36 | | 2. from | + // | | 68 | | 3. to | + // | | 100 | | 4. amount | + // | Data | | | assetData: | + // | | 132 | 32 | assetData Length | + // | | 164 | ** | assetData Contents | + // + // (*): offset is computed from start of function parameters, so offset + // by an additional 4 bytes in the calldata. + // + // (**): see table below to compute length of assetData Contents + // + // WARNING: The ABIv2 specification allows additional padding between + // the Params and Data section. This will result in a larger + // offset to assetData. + + // Asset data itself is encoded as follows: + // + // | Area | Offset | Length | Contents | + // |----------|--------|---------|-------------------------------------| + // | Header | 0 | 4 | function selector | + // | Params | | 1 * 32 | function parameters: | + // | | 4 | 12 + 20 | 1. token address | + + // We construct calldata for the `token.transferFrom` ABI. + // The layout of this calldata is in the table below. + // + // | Area | Offset | Length | Contents | + // |----------|--------|---------|-------------------------------------| + // | Header | 0 | 4 | function selector | + // | Params | | 3 * 32 | function parameters: | + // | | 4 | | 1. from | + // | | 36 | | 2. to | + // | | 68 | | 3. amount | + + /////// Read token address from calldata /////// + // * The token address is stored in `assetData`. + // + // * The "offset to assetData" is stored at offset 4 in the calldata (table 1). + // [assetDataOffsetFromParams = calldataload(4)] + // + // * Notes that the "offset to assetData" is relative to the "Params" area of calldata; + // add 4 bytes to account for the length of the "Header" area (table 1). + // [assetDataOffsetFromHeader = assetDataOffsetFromParams + 4] + // + // * The "token address" is offset 32+4=36 bytes into "assetData" (tables 1 & 2). + // [tokenOffset = assetDataOffsetFromHeader + 36 = calldataload(4) + 4 + 36] let token := calldataload(add(calldataload(4), 40)) /////// Setup Header Area /////// |