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

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>

3 files changed, 8 insertions, 2 deletions

diff --git a/src/cmd/link/internal/sym/symbols.go b/src/cmd/link/internal/sym/symbols.go
index d7266c840b..f0fcf2361b 100644
--- a/src/cmd/link/internal/sym/symbols.go
+++ b/src/cmd/link/internal/sym/symbols.go
@@ -43,6 +43,8 @@ func NewSymbols() *Symbols {
 	hash := make([]map[string]*Symbol, SymVerStatic)
 	// Preallocate about 2mb for hash of non static symbols
 	hash[0] = make(map[string]*Symbol, 100000)
+	// And another 1mb for internal ABI text symbols.
+	hash[SymVerABIInternal] = make(map[string]*Symbol, 50000)
 	return &Symbols{
 		hash:   hash,
 		Allsym: make([]*Symbol, 0, 100000),
diff --git a/src/cmd/link/internal/sym/symkind.go b/src/cmd/link/internal/sym/symkind.go
index b1756d6145..6e1e1b58a1 100644
--- a/src/cmd/link/internal/sym/symkind.go
+++ b/src/cmd/link/internal/sym/symkind.go
@@ -109,6 +109,9 @@ const (
 	SDWARFRANGE
 	SDWARFLOC
 	SDWARFMISC // Not really a section; informs/affects other DWARF section generation
+
+	// ABI aliases (these never appear in the output)
+	SABIALIAS
 )
 
 // AbiSymKindToSymKind maps values read from object files (which are
@@ -126,6 +129,7 @@ var AbiSymKindToSymKind = [...]SymKind{
 	SDWARFRANGE,
 	SDWARFLOC,
 	SDWARFMISC,
+	SABIALIAS,
 }
 
 // ReadOnly are the symbol kinds that form read-only sections. In some
diff --git a/src/cmd/link/internal/sym/symkind_string.go b/src/cmd/link/internal/sym/symkind_string.go
index 7428503b1c..4da6c656f7 100644
--- a/src/cmd/link/internal/sym/symkind_string.go
+++ b/src/cmd/link/internal/sym/symkind_string.go
@@ -4,9 +4,9 @@ package sym
 
 import "strconv"
 
-const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASBSSSNOPTRBSSSTLSBSSSXCOFFTOCSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILEPATHSCONSTSDYNIMPORTSHOSTOBJSDWARFSECTSDWARFINFOSDWARFRANGESDWARFLOCSDWARFMISC"
+const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASBSSSNOPTRBSSSTLSBSSSXCOFFTOCSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILEPATHSCONSTSDYNIMPORTSHOSTOBJSDWARFSECTSDWARFINFOSDWARFRANGESDWARFLOCSDWARFMISCSABIALIAS"
 
-var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 47, 54, 61, 69, 79, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 214, 220, 229, 237, 244, 254, 262, 267, 271, 280, 287, 296, 301, 313, 325, 342, 359, 368, 374, 384, 392, 402, 412, 423, 432, 442}
+var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 47, 54, 61, 69, 79, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 214, 220, 229, 237, 244, 254, 262, 267, 271, 280, 287, 296, 301, 313, 325, 342, 359, 368, 374, 384, 392, 402, 412, 423, 432, 442, 451}
 
 func (i SymKind) String() string {
 	if i >= SymKind(len(_SymKind_index)-1) {