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cmd/compile, cmd/link: separate stable and internal ABIs

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This implements compiler and linker support for separating the
function calling ABI into two ABIs: a stable and an internal ABI. At
the moment, the two ABIs are identical, but we'll be able to evolve
the internal ABI without breaking existing assembly code that depends
on the stable ABI for calling to and from Go.

The Go compiler generates internal ABI symbols for all Go functions.
It uses the symabis information produced by the assembler to create
ABI wrappers whenever it encounters a body-less Go function that's
defined in assembly or a Go function that's referenced from assembly.

Since the two ABIs are currently identical, for the moment this is
implemented using "ABI alias" symbols, which are just forwarding
references to the native ABI symbol for a function. This way there's
no actual code involved in the ABI wrapper, which is good because
we're not deriving any benefit from it right now. Once the ABIs
diverge, we can eliminate ABI aliases.

The linker represents these different ABIs internally as different
versions of the same symbol. This way, the linker keeps us honest,
since every symbol definition and reference also specifies its
version. The linker is responsible for resolving ABI aliases.

Fixes #27539.

Change-Id: I197c52ec9f8fc435db8f7a4259029b20f6d65e95
Reviewed-on: https://go-review.googlesource.com/c/147160
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Austin Clements 2018-11-01 12:30:23 -04:00
parent 1794ee6829
commit 685aca45dc
20 changed files with 194 additions and 32 deletions
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32
src/cmd/link/internal/ld/lib.go
View file

@ -169,7 +169,7 @@ func (ctxt *Link) DynlinkingGo() bool {
// CanUsePlugins returns whether a plugins can be used
func (ctxt *Link) CanUsePlugins() bool {
return ctxt.Syms.ROLookup("plugin.Open", 0) != nil
return ctxt.Syms.ROLookup("plugin.Open", sym.SymVerABIInternal) != nil
}
// UseRelro returns whether to make use of "read only relocations" aka
@ -635,6 +635,19 @@ func (ctxt *Link) loadlib() {
}
ctxt.Textp = textp
}
// Resolve ABI aliases in the list of cgo-exported functions.
// This is necessary because we load the ABI0 symbol for all
// cgo exports.
for i, s := range dynexp {
if s.Type != sym.SABIALIAS {
continue
}
t := resolveABIAlias(s)
t.Attr |= s.Attr
t.SetExtname(s.Extname())
dynexp[i] = t
}
}
// mangleTypeSym shortens the names of symbols that represent Go types
@ -651,7 +664,7 @@ func (ctxt *Link) loadlib() {
// those programs loaded dynamically in multiple parts need these
// symbols to have entries in the symbol table.
func (ctxt *Link) mangleTypeSym() {
if ctxt.BuildMode != BuildModeShared && !ctxt.linkShared && ctxt.BuildMode != BuildModePlugin && ctxt.Syms.ROLookup("plugin.Open", 0) == nil {
if ctxt.BuildMode != BuildModeShared && !ctxt.linkShared && ctxt.BuildMode != BuildModePlugin && !ctxt.CanUsePlugins() {
return
}
@ -1801,6 +1814,21 @@ func ldshlibsyms(ctxt *Link, shlib string) {
gcdataLocations[elfsym.Value+2*uint64(ctxt.Arch.PtrSize)+8+1*uint64(ctxt.Arch.PtrSize)] = lsym
}
}
// For function symbols, we don't know what ABI is
// available, so alias it under both ABIs.
//
// TODO(austin): This is almost certainly wrong once
// the ABIs are actually different. We might have to
// mangle Go function names in the .so to include the
// ABI.
if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC {
alias := ctxt.Syms.Lookup(elfsym.Name, sym.SymVerABIInternal)
if alias.Type != 0 {
continue
}
alias.Type = sym.SABIALIAS
alias.R = []sym.Reloc{{Sym: lsym}}
}
}
gcdataAddresses := make(map[*sym.Symbol]uint64)
if ctxt.Arch.Family == sys.ARM64 {