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[dev.link] cmd/compile, cmd/asm: assign index to symbols

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We are planning to use indices for symbol references, instead of
symbol names. Here we assign indices to symbols defined in the
package being compiled, and propagate the indices to the
dependent packages in the export data.

A symbol is referenced by a tuple, (package index, symbol index).
Normally, for a given symbol, this index is unique, and the
symbol index is globally consistent (but with exceptions, see
below). The package index is local to a compilation. For example,
when compiling the fmt package, fmt.Println gets assigned index
25, then all packages that reference fmt.Println will refer it
as (X, 25) with some X. X is the index for the fmt package, which
may differ in different compilations.

There are some symbols that do not have clear package affiliation,
such as dupOK symbols and linknamed symbols. We cannot give them
globally consistent indices. We categorize them as non-package
symbols, assign them with package index 1 and a symbol index that
is only meaningful locally.

Currently nothing will consume the indices.

All this is behind a flag, -newobj. The flag needs to be set for
all builds (-gcflags=all=-newobj -asmflags=all=-newobj), or none.

Change-Id: I18e489c531e9a9fbc668519af92c6116b7308cab
Reviewed-on: https://go-review.googlesource.com/c/go/+/196029
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Cherry Zhang 2019-09-11 16:17:01 -04:00
parent cd75cf4bc0
commit 53b7c18284
9 changed files with 194 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

30
src/cmd/internal/obj/link.go
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@ -388,6 +388,10 @@ type LSym struct {
R []Reloc
Func *FuncInfo
Pkg string
PkgIdx int32
SymIdx int32 // TODO: replace RefIdx
}
// A FuncInfo contains extra fields for STEXT symbols.
@ -460,7 +464,7 @@ const (
)
// Attribute is a set of symbol attributes.
type Attribute uint16
type Attribute uint32
const (
AttrDuplicateOK Attribute = 1 << iota
@ -501,6 +505,10 @@ const (
// keep unwinding beyond this frame.
AttrTopFrame
// Indexed indicates this symbol has been assigned with an index (when using the
// new object file format).
AttrIndexed
// attrABIBase is the value at which the ABI is encoded in
// Attribute. This must be last; all bits after this are
// assumed to be an ABI value.
@ -524,6 +532,7 @@ func (a Attribute) NoFrame() bool { return a&AttrNoFrame != 0 }
func (a Attribute) Static() bool { return a&AttrStatic != 0 }
func (a Attribute) WasInlined() bool { return a&AttrWasInlined != 0 }
func (a Attribute) TopFrame() bool { return a&AttrTopFrame != 0 }
func (a Attribute) Indexed() bool { return a&AttrIndexed != 0 }
func (a *Attribute) Set(flag Attribute, value bool) {
if value {
@ -558,6 +567,7 @@ var textAttrStrings = [...]struct {
{bit: AttrStatic, s: "STATIC"},
{bit: AttrWasInlined, s: ""},
{bit: AttrTopFrame, s: "TOPFRAME"},
{bit: AttrIndexed, s: ""},
}
// TextAttrString formats a for printing in as part of a TEXT prog.
@ -626,6 +636,15 @@ type Pcdata struct {
P []byte
}
// Package Index.
const (
PkgIdxNone = (1<<31 - 1) - iota // Non-package symbols
PkgIdxBuiltin // Predefined symbols // TODO: not used for now, we could use it for compiler-generated symbols like runtime.newobject
PkgIdxSelf // Symbols defined in the current package
PkgIdxInvalid = 0
// The index of other referenced packages starts from 1.
)
// Link holds the context for writing object code from a compiler
// to be linker input or for reading that input into the linker.
type Link struct {
@ -638,6 +657,7 @@ type Link struct {
Flag_dynlink bool
Flag_optimize bool
Flag_locationlists bool
Flag_newobj bool // use new object file format
Bso *bufio.Writer
Pathname string
hashmu sync.Mutex // protects hash, funchash
@ -671,6 +691,14 @@ type Link struct {
// TODO(austin): Replace this with ABI wrappers once the ABIs
// actually diverge.
ABIAliases []*LSym
// pkgIdx maps package path to index. The index is used for
// symbol reference in the object file.
pkgIdx map[string]int32
defs []*LSym // list of defined symbols in the current package
nonpkgdefs []*LSym // list of defined non-package symbols
nonpkgrefs []*LSym // list of referenced non-package symbols
}
func (ctxt *Link) Diag(format string, args ...interface{}) {