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core/asm: assembly parser label fixes (#20210)

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* core/asm: Fix encoding of pushed labels

EVM uses big-endian byte-order, so to pad a label value to 4 bytes,
zeros must be added to the front, not the end.

* core/asm: Fix PC calculations when a label is pushed

Incrementing PC by 5 is only correct if the label appears after a jump,
in which case there is an implicit push. When it appears after an explicit
push, PC should only be incremented by 4.

* core/asm: Allow JUMP with no argument

This way, a label can be pushed explicitly, or loaded from memory to
implement a jump table.
This commit is contained in:
Michael Forney
2019-10-29 05:47:18 -07:00
committed by Felix Lange
parent ecdbb402ee
commit b0b277525c
2 changed files with 81 additions and 3 deletions
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13
core/asm/compiler.go
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@ -57,6 +57,7 @@ func NewCompiler(debug bool) *Compiler {
// second stage to push labels and determine the right
// position.
func (c *Compiler) Feed(ch <-chan token) {
var prev token
for i := range ch {
switch i.typ {
case number:
@ -73,10 +74,14 @@ func (c *Compiler) Feed(ch <-chan token) {
c.labels[i.text] = c.pc
c.pc++
case label:
c.pc += 5
c.pc += 4
if prev.typ == element && isJump(prev.text) {
c.pc++
}
}
c.tokens = append(c.tokens, i)
prev = i
}
if c.debug {
fmt.Fprintln(os.Stderr, "found", len(c.labels), "labels")
@ -181,6 +186,8 @@ func (c *Compiler) compileElement(element token) error {
pos := big.NewInt(int64(c.labels[rvalue.text])).Bytes()
pos = append(make([]byte, 4-len(pos)), pos...)
c.pushBin(pos)
case lineEnd:
c.pos--
default:
return compileErr(rvalue, rvalue.text, "number, string or label")
}
@ -201,8 +208,8 @@ func (c *Compiler) compileElement(element token) error {
case stringValue:
value = []byte(rvalue.text[1 : len(rvalue.text)-1])
case label:
value = make([]byte, 4)
copy(value, big.NewInt(int64(c.labels[rvalue.text])).Bytes())
value = big.NewInt(int64(c.labels[rvalue.text])).Bytes()
value = append(make([]byte, 4-len(value)), value...)
default:
return compileErr(rvalue, rvalue.text, "number, string or label")
}