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package binary
import (
"bytes"
"debug/dwarf"
"errors"
"fmt"
"io"
"github.com/tetratelabs/wazero/api"
"github.com/tetratelabs/wazero/internal/leb128"
"github.com/tetratelabs/wazero/internal/wasm"
"github.com/tetratelabs/wazero/internal/wasmdebug"
)
// DecodeModule implements wasm.DecodeModule for the WebAssembly 1.0 (20191205) Binary Format
// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#binary-format%E2%91%A0
func DecodeModule(
binary []byte,
enabledFeatures api.CoreFeatures,
memoryLimitPages uint32,
memoryCapacityFromMax,
dwarfEnabled, storeCustomSections bool,
) (*wasm.Module, error) {
r := bytes.NewReader(binary)
// Magic number.
buf := make([]byte, 4)
if _, err := io.ReadFull(r, buf); err != nil || !bytes.Equal(buf, Magic) {
return nil, ErrInvalidMagicNumber
}
// Version.
if _, err := io.ReadFull(r, buf); err != nil || !bytes.Equal(buf, version) {
return nil, ErrInvalidVersion
}
memSizer := newMemorySizer(memoryLimitPages, memoryCapacityFromMax)
m := &wasm.Module{}
var info, line, str, abbrev, ranges []byte // For DWARF Data.
for {
// TODO: except custom sections, all others are required to be in order, but we aren't checking yet.
// See https://www.w3.org/TR/2019/REC-wasm-core-1-20191205/#modules%E2%91%A0%E2%93%AA
sectionID, err := r.ReadByte()
if err == io.EOF {
break
} else if err != nil {
return nil, fmt.Errorf("read section id: %w", err)
}
sectionSize, _, err := leb128.DecodeUint32(r)
if err != nil {
return nil, fmt.Errorf("get size of section %s: %v", wasm.SectionIDName(sectionID), err)
}
sectionContentStart := r.Len()
switch sectionID {
case wasm.SectionIDCustom:
// First, validate the section and determine if the section for this name has already been set
name, nameSize, decodeErr := decodeUTF8(r, "custom section name")
if decodeErr != nil {
err = decodeErr
break
} else if sectionSize < nameSize {
err = fmt.Errorf("malformed custom section %s", name)
break
} else if name == "name" && m.NameSection != nil {
err = fmt.Errorf("redundant custom section %s", name)
break
}
// Now, either decode the NameSection or CustomSection
limit := sectionSize - nameSize
var c *wasm.CustomSection
if name != "name" {
if storeCustomSections || dwarfEnabled {
c, err = decodeCustomSection(r, name, uint64(limit))
if err != nil {
return nil, fmt.Errorf("failed to read custom section name[%s]: %w", name, err)
}
m.CustomSections = append(m.CustomSections, c)
if dwarfEnabled {
switch name {
case ".debug_info":
info = c.Data
case ".debug_line":
line = c.Data
case ".debug_str":
str = c.Data
case ".debug_abbrev":
abbrev = c.Data
case ".debug_ranges":
ranges = c.Data
}
}
} else {
if _, err = io.CopyN(io.Discard, r, int64(limit)); err != nil {
return nil, fmt.Errorf("failed to skip name[%s]: %w", name, err)
}
}
} else {
m.NameSection, err = decodeNameSection(r, uint64(limit))
}
case wasm.SectionIDType:
m.TypeSection, err = decodeTypeSection(enabledFeatures, r)
case wasm.SectionIDImport:
m.ImportSection, m.ImportPerModule, m.ImportFunctionCount, m.ImportGlobalCount, m.ImportMemoryCount, m.ImportTableCount, err = decodeImportSection(r, memSizer, memoryLimitPages, enabledFeatures)
if err != nil {
return nil, err // avoid re-wrapping the error.
}
case wasm.SectionIDFunction:
m.FunctionSection, err = decodeFunctionSection(r)
case wasm.SectionIDTable:
m.TableSection, err = decodeTableSection(r, enabledFeatures)
case wasm.SectionIDMemory:
m.MemorySection, err = decodeMemorySection(r, enabledFeatures, memSizer, memoryLimitPages)
case wasm.SectionIDGlobal:
if m.GlobalSection, err = decodeGlobalSection(r, enabledFeatures); err != nil {
return nil, err // avoid re-wrapping the error.
}
case wasm.SectionIDExport:
m.ExportSection, m.Exports, err = decodeExportSection(r)
case wasm.SectionIDStart:
if m.StartSection != nil {
return nil, errors.New("multiple start sections are invalid")
}
m.StartSection, err = decodeStartSection(r)
case wasm.SectionIDElement:
m.ElementSection, err = decodeElementSection(r, enabledFeatures)
case wasm.SectionIDCode:
m.CodeSection, err = decodeCodeSection(r)
case wasm.SectionIDData:
m.DataSection, err = decodeDataSection(r, enabledFeatures)
case wasm.SectionIDDataCount:
if err := enabledFeatures.RequireEnabled(api.CoreFeatureBulkMemoryOperations); err != nil {
return nil, fmt.Errorf("data count section not supported as %v", err)
}
m.DataCountSection, err = decodeDataCountSection(r)
default:
err = ErrInvalidSectionID
}
readBytes := sectionContentStart - r.Len()
if err == nil && int(sectionSize) != readBytes {
err = fmt.Errorf("invalid section length: expected to be %d but got %d", sectionSize, readBytes)
}
if err != nil {
return nil, fmt.Errorf("section %s: %v", wasm.SectionIDName(sectionID), err)
}
}
if dwarfEnabled {
d, _ := dwarf.New(abbrev, nil, nil, info, line, nil, ranges, str)
m.DWARFLines = wasmdebug.NewDWARFLines(d)
}
functionCount, codeCount := m.SectionElementCount(wasm.SectionIDFunction), m.SectionElementCount(wasm.SectionIDCode)
if functionCount != codeCount {
return nil, fmt.Errorf("function and code section have inconsistent lengths: %d != %d", functionCount, codeCount)
}
return m, nil
}
// memorySizer derives min, capacity and max pages from decoded wasm.
type memorySizer func(minPages uint32, maxPages *uint32) (min uint32, capacity uint32, max uint32)
// newMemorySizer sets capacity to minPages unless max is defined and
// memoryCapacityFromMax is true.
func newMemorySizer(memoryLimitPages uint32, memoryCapacityFromMax bool) memorySizer {
return func(minPages uint32, maxPages *uint32) (min, capacity, max uint32) {
if maxPages != nil {
if memoryCapacityFromMax {
return minPages, *maxPages, *maxPages
}
// This is an invalid value: let it propagate, we will fail later.
if *maxPages > wasm.MemoryLimitPages {
return minPages, minPages, *maxPages
}
// This is a valid value, but it goes over the run-time limit: return the limit.
if *maxPages > memoryLimitPages {
return minPages, minPages, memoryLimitPages
}
return minPages, minPages, *maxPages
}
if memoryCapacityFromMax {
return minPages, memoryLimitPages, memoryLimitPages
}
return minPages, minPages, memoryLimitPages
}
}
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