From c8dcaeb25deddac52cfca6ae6882ce94780582d3 Mon Sep 17 00:00:00 2001 From: Russ Cox Date: Tue, 26 Feb 2013 22:38:14 -0500 Subject: cmd/ld, runtime: adjust symbol table representation This CL changes the encoding used for the Go symbol table, stored in the binary and used at run time. It does not change any of the semantics or structure: the bits are just packed a little differently. The comment at the top of runtime/symtab.c describes the new format. Compared to the Go 1.0 format, the main changes are: * Store symbol addresses as full-pointer-sized host-endian values. (For 6g, this means addresses are 64-bit little-endian.) * Store other values (frame sizes and so on) varint-encoded. The second change more than compensates for the first: for the godoc binary on OS X/amd64, the new symbol table is 8% smaller than the old symbol table (1,425,668 down from 1,546,276). This is a required step for allowing the host linker (gcc) to write the final Go binary, since it will have to fill in the symbol address slots (so the slots must be host-endian) and on 64-bit systems it may choose addresses above 4 GB. R=golang-dev, iant CC=golang-dev https://golang.org/cl/7403054 --- src/pkg/debug/gosym/symtab.go | 123 ++++++++++++++++++++++++++++++++++++------ 1 file changed, 108 insertions(+), 15 deletions(-) (limited to 'src/pkg/debug') diff --git a/src/pkg/debug/gosym/symtab.go b/src/pkg/debug/gosym/symtab.go index cc01e0b9d6..81ed4fb27d 100644 --- a/src/pkg/debug/gosym/symtab.go +++ b/src/pkg/debug/gosym/symtab.go @@ -99,31 +99,116 @@ type Table struct { } type sym struct { - value uint32 - gotype uint32 + value uint64 + gotype uint64 typ byte name []byte } -var littleEndianSymtab = []byte{0xFE, 0xFF, 0xFF, 0xFF, 0x00, 0x00} +var littleEndianSymtab = []byte{0xFD, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00} +var bigEndianSymtab = []byte{0xFF, 0xFF, 0xFF, 0xFD, 0x00, 0x00, 0x00} + +var oldLittleEndianSymtab = []byte{0xFE, 0xFF, 0xFF, 0xFF, 0x00, 0x00} func walksymtab(data []byte, fn func(sym) error) error { var order binary.ByteOrder = binary.BigEndian - if bytes.HasPrefix(data, littleEndianSymtab) { + newTable := false + switch { + case bytes.HasPrefix(data, oldLittleEndianSymtab): + // Same as Go 1.0, but little endian. + // Format was used during interim development between Go 1.0 and Go 1.1. + // Should not be widespread, but easy to support. data = data[6:] order = binary.LittleEndian + case bytes.HasPrefix(data, bigEndianSymtab): + newTable = true + case bytes.HasPrefix(data, littleEndianSymtab): + newTable = true + order = binary.LittleEndian + } + var ptrsz int + if newTable { + if len(data) < 8 { + return &DecodingError{len(data), "unexpected EOF", nil} + } + ptrsz = int(data[7]) + if ptrsz != 4 && ptrsz != 8 { + return &DecodingError{7, "invalid pointer size", ptrsz} + } + data = data[8:] } var s sym p := data - for len(p) >= 6 { - s.value = order.Uint32(p[0:4]) - typ := p[4] - if typ&0x80 == 0 { - return &DecodingError{len(data) - len(p) + 4, "bad symbol type", typ} + for len(p) >= 4 { + var typ byte + if newTable { + // Symbol type, value, Go type. + typ = p[0] & 0x3F + wideValue := p[0]&0x40 != 0 + goType := p[0]&0x80 != 0 + if typ < 26 { + typ += 'A' + } else { + typ += 'a' - 26 + } + s.typ = typ + p = p[1:] + if wideValue { + if len(p) < ptrsz { + return &DecodingError{len(data), "unexpected EOF", nil} + } + // fixed-width value + if ptrsz == 8 { + s.value = order.Uint64(p[0:8]) + p = p[8:] + } else { + s.value = uint64(order.Uint32(p[0:4])) + p = p[4:] + } + } else { + // varint value + s.value = 0 + shift := uint(0) + for len(p) > 0 && p[0]&0x80 != 0 { + s.value |= uint64(p[0]&0x7F) << shift + shift += 7 + p = p[1:] + } + if len(p) == 0 { + return &DecodingError{len(data), "unexpected EOF", nil} + } + s.value |= uint64(p[0]) << shift + p = p[1:] + } + if goType { + if len(p) < ptrsz { + return &DecodingError{len(data), "unexpected EOF", nil} + } + // fixed-width go type + if ptrsz == 8 { + s.gotype = order.Uint64(p[0:8]) + p = p[8:] + } else { + s.gotype = uint64(order.Uint32(p[0:4])) + p = p[4:] + } + } + } else { + // Value, symbol type. + s.value = uint64(order.Uint32(p[0:4])) + if len(p) < 5 { + return &DecodingError{len(data), "unexpected EOF", nil} + } + typ = p[4] + if typ&0x80 == 0 { + return &DecodingError{len(data) - len(p) + 4, "bad symbol type", typ} + } + typ &^= 0x80 + s.typ = typ + p = p[5:] } - typ &^= 0x80 - s.typ = typ - p = p[5:] + + // Name. var i int var nnul int for i = 0; i < len(p); i++ { @@ -142,13 +227,21 @@ func walksymtab(data []byte, fn func(sym) error) error { } } } - if i+nnul+4 > len(p) { + if len(p) < i+nnul { return &DecodingError{len(data), "unexpected EOF", nil} } s.name = p[0:i] i += nnul - s.gotype = order.Uint32(p[i : i+4]) - p = p[i+4:] + p = p[i:] + + if !newTable { + if len(p) < 4 { + return &DecodingError{len(data), "unexpected EOF", nil} + } + // Go type. + s.gotype = uint64(order.Uint32(p[:4])) + p = p[4:] + } fn(s) } return nil -- cgit v1.3