| // Copyright 2013 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // NOTE: There are *three* independent implementations of this object |
| // file format in the Go source tree: |
| // |
| // - cmd/internal/goobj/read.go (used by cmd/addr2line, cmd/nm, cmd/objdump, cmd/pprof) |
| // - cmd/internal/obj/objfile.go (used by cmd/asm and cmd/compile) |
| // - cmd/link/internal/objfile.go (used by cmd/link) |
| // |
| // When changing the object file format, remember to change all three. |
| |
| // Originally, Go object files were Plan 9 object files, but no longer. |
| // Now they are more like standard object files, in that each symbol is defined |
| // by an associated memory image (bytes) and a list of relocations to apply |
| // during linking. We do not (yet?) use a standard file format, however. |
| // For now, the format is chosen to be as simple as possible to read and write. |
| // It may change for reasons of efficiency, or we may even switch to a |
| // standard file format if there are compelling benefits to doing so. |
| // See golang.org/s/go13linker for more background. |
| // |
| // The file format is: |
| // |
| // - magic header: "\x00\x00go19ld" |
| // - byte 1 - version number |
| // - sequence of strings giving dependencies (imported packages) |
| // - empty string (marks end of sequence) |
| // - sequence of symbol references used by the defined symbols |
| // - byte 0xff (marks end of sequence) |
| // - sequence of integer lengths: |
| // - total data length |
| // - total number of relocations |
| // - total number of pcdata |
| // - total number of automatics |
| // - total number of funcdata |
| // - total number of files |
| // - data, the content of the defined symbols |
| // - sequence of defined symbols |
| // - byte 0xff (marks end of sequence) |
| // - magic footer: "\xff\xffgo19ld" |
| // |
| // All integers are stored in a zigzag varint format. |
| // See golang.org/s/go12symtab for a definition. |
| // |
| // Data blocks and strings are both stored as an integer |
| // followed by that many bytes. |
| // |
| // A symbol reference is a string name followed by a version. |
| // |
| // A symbol points to other symbols using an index into the symbol |
| // reference sequence. Index 0 corresponds to a nil symbol pointer. |
| // In the symbol layout described below "symref index" stands for this |
| // index. |
| // |
| // Each symbol is laid out as the following fields: |
| // |
| // - byte 0xfe (sanity check for synchronization) |
| // - type [byte] |
| // - name & version [symref index] |
| // - flags [int] |
| // 1<<0 dupok |
| // 1<<1 local |
| // 1<<2 add to typelink table |
| // - size [int] |
| // - gotype [symref index] |
| // - p [data block] |
| // - nr [int] |
| // - r [nr relocations, sorted by off] |
| // |
| // If type == STEXT, there are a few more fields: |
| // |
| // - args [int] |
| // - locals [int] |
| // - nosplit [int] |
| // - flags [int] |
| // 1<<0 leaf |
| // 1<<1 C function |
| // 1<<2 function may call reflect.Type.Method |
| // 1<<3 function compiled with -shared |
| // - nlocal [int] |
| // - local [nlocal automatics] |
| // - pcln [pcln table] |
| // |
| // Each relocation has the encoding: |
| // |
| // - off [int] |
| // - siz [int] |
| // - type [int] |
| // - add [int] |
| // - sym [symref index] |
| // |
| // Each local has the encoding: |
| // |
| // - asym [symref index] |
| // - offset [int] |
| // - type [int] |
| // - gotype [symref index] |
| // |
| // The pcln table has the encoding: |
| // |
| // - pcsp [data block] |
| // - pcfile [data block] |
| // - pcline [data block] |
| // - pcinline [data block] |
| // - npcdata [int] |
| // - pcdata [npcdata data blocks] |
| // - nfuncdata [int] |
| // - funcdata [nfuncdata symref index] |
| // - funcdatasym [nfuncdata ints] |
| // - nfile [int] |
| // - file [nfile symref index] |
| // - ninlinedcall [int] |
| // - inlinedcall [ninlinedcall int symref int symref] |
| // |
| // The file layout and meaning of type integers are architecture-independent. |
| // |
| // TODO(rsc): The file format is good for a first pass but needs work. |
| // - There are SymID in the object file that should really just be strings. |
| package objabi |
