cmd/ld: host linking support for linux/amd64

Still to do: non-linux and non-amd64.
It may work on other ELF-based amd64 systems too, but untested.

"go test -ldflags -hostobj $GOROOT/misc/cgo/test" passes.

Much may yet change, but this seems a reasonable checkpoint.

R=iant
CC=golang-dev
https://golang.org/cl/7369057

3 files changed, 20 insertions, 14 deletions

diff --git a/src/cmd/6l/asm.c b/src/cmd/6l/asm.c
index 5fb75ba4d0..627e10af0a 100644
--- a/src/cmd/6l/asm.c
+++ b/src/cmd/6l/asm.c
@@ -131,7 +131,7 @@ adddynrel(Sym *s, Reloc *r)
 
 	// Handle relocations found in ELF object files.
 	case 256 + R_X86_64_PC32:
-		if(targ->dynimpname != nil && !targ->dynexport)
+		if(targ->dynimpname != nil && !(targ->cgoexport & CgoExportDynamic))
 			diag("unexpected R_X86_64_PC32 relocation for dynamic symbol %s", targ->name);
 		if(targ->type == 0 || targ->type == SXREF)
 			diag("unknown symbol %s in pcrel", targ->name);
@@ -142,7 +142,7 @@ adddynrel(Sym *s, Reloc *r)
 	case 256 + R_X86_64_PLT32:
 		r->type = D_PCREL;
 		r->add += 4;
-		if(targ->dynimpname != nil && !targ->dynexport) {
+		if(targ->dynimpname != nil && !(targ->cgoexport & CgoExportDynamic)) {
 			addpltsym(targ);
 			r->sym = lookup(".plt", 0);
 			r->add += targ->plt;
@@ -150,7 +150,7 @@ adddynrel(Sym *s, Reloc *r)
 		return;
 	
 	case 256 + R_X86_64_GOTPCREL:
-		if(targ->dynimpname == nil || targ->dynexport) {
+		if(targ->dynimpname == nil || (targ->cgoexport & CgoExportDynamic)) {
 			// have symbol
 			if(r->off >= 2 && s->p[r->off-2] == 0x8b) {
 				// turn MOVQ of GOT entry into LEAQ of symbol itself
@@ -171,7 +171,7 @@ adddynrel(Sym *s, Reloc *r)
 		return;
 	
 	case 256 + R_X86_64_64:
-		if(targ->dynimpname != nil && !targ->dynexport)
+		if(targ->dynimpname != nil && !(targ->cgoexport & CgoExportDynamic))
 			diag("unexpected R_X86_64_64 relocation for dynamic symbol %s", targ->name);
 		r->type = D_ADDR;
 		return;
@@ -182,12 +182,12 @@ adddynrel(Sym *s, Reloc *r)
 	case 512 + MACHO_X86_64_RELOC_BRANCH*2 + 0:
 		// TODO: What is the difference between all these?
 		r->type = D_ADDR;
-		if(targ->dynimpname != nil && !targ->dynexport)
+		if(targ->dynimpname != nil && !(targ->cgoexport & CgoExportDynamic))
 			diag("unexpected reloc for dynamic symbol %s", targ->name);
 		return;
 
 	case 512 + MACHO_X86_64_RELOC_BRANCH*2 + 1:
-		if(targ->dynimpname != nil && !targ->dynexport) {
+		if(targ->dynimpname != nil && !(targ->cgoexport & CgoExportDynamic)) {
 			addpltsym(targ);
 			r->sym = lookup(".plt", 0);
 			r->add = targ->plt;
@@ -201,12 +201,12 @@ adddynrel(Sym *s, Reloc *r)
 	case 512 + MACHO_X86_64_RELOC_SIGNED_2*2 + 1:
 	case 512 + MACHO_X86_64_RELOC_SIGNED_4*2 + 1:
 		r->type = D_PCREL;
-		if(targ->dynimpname != nil && !targ->dynexport)
+		if(targ->dynimpname != nil && !(targ->cgoexport & CgoExportDynamic))
 			diag("unexpected pc-relative reloc for dynamic symbol %s", targ->name);
 		return;
 
 	case 512 + MACHO_X86_64_RELOC_GOT_LOAD*2 + 1:
-		if(targ->dynimpname == nil || targ->dynexport) {
+		if(targ->dynimpname == nil || (targ->cgoexport & CgoExportDynamic)) {
 			// have symbol
 			// turn MOVQ of GOT entry into LEAQ of symbol itself
 			if(r->off < 2 || s->p[r->off-2] != 0x8b) {
@@ -219,7 +219,7 @@ adddynrel(Sym *s, Reloc *r)
 		}
 		// fall through
 	case 512 + MACHO_X86_64_RELOC_GOT*2 + 1:
-		if(targ->dynimpname == nil || targ->dynexport)
+		if(targ->dynimpname == nil || (targ->cgoexport & CgoExportDynamic))
 			diag("unexpected GOT reloc for non-dynamic symbol %s", targ->name);
 		addgotsym(targ);
 		r->type = D_PCREL;
@@ -229,7 +229,7 @@ adddynrel(Sym *s, Reloc *r)
 	}
 	
 	// Handle references to ELF symbols from our own object files.
-	if(targ->dynimpname == nil || targ->dynexport)
+	if(targ->dynimpname == nil || (targ->cgoexport & CgoExportDynamic))
 		return;
 
 	switch(r->type) {
@@ -470,7 +470,7 @@ adddynsym(Sym *s)
 		adduint32(d, addstring(lookup(".dynstr", 0), name));
 		/* type */
 		t = STB_GLOBAL << 4;
-		if(s->dynexport && (s->type&SMASK) == STEXT)
+		if((s->cgoexport & CgoExportDynamic) && (s->type&SMASK) == STEXT)
 			t |= STT_FUNC;
 		else
 			t |= STT_OBJECT;
@@ -480,7 +480,7 @@ adddynsym(Sym *s)
 		adduint8(d, 0);
 	
 		/* section where symbol is defined */
-		if(!s->dynexport && s->dynimpname != nil)
+		if(!(s->cgoexport & CgoExportDynamic) && s->dynimpname != nil)
 			adduint16(d, SHN_UNDEF);
 		else {
 			switch(s->type) {
@@ -510,7 +510,7 @@ adddynsym(Sym *s)
 		/* size of object */
 		adduint64(d, s->size);
 	
-		if(!s->dynexport && s->dynimplib && needlib(s->dynimplib)) {
+		if(!(s->cgoexport & CgoExportDynamic) && s->dynimplib && needlib(s->dynimplib)) {
 			elfwritedynent(lookup(".dynamic", 0), DT_NEEDED,
 				addstring(lookup(".dynstr", 0), s->dynimplib));
 		}
diff --git a/src/cmd/6l/l.h b/src/cmd/6l/l.h
index ffb8a45522..22fb23b1b7 100644
--- a/src/cmd/6l/l.h
+++ b/src/cmd/6l/l.h
@@ -144,7 +144,7 @@ struct	Sym
 	short	version;
 	uchar	dupok;
 	uchar	reachable;
-	uchar	dynexport;
+	uchar	cgoexport;
 	uchar	special;
 	uchar	stkcheck;
 	uchar	hide;
diff --git a/src/cmd/6l/obj.c b/src/cmd/6l/obj.c
index 10e4a98601..6ced8be7fd 100644
--- a/src/cmd/6l/obj.c
+++ b/src/cmd/6l/obj.c
@@ -83,6 +83,7 @@ main(int argc, char *argv[])
 	INITRND = -1;
 	INITENTRY = 0;
 	LIBINITENTRY = 0;
+	linkmode = LinkInternal; // TODO: LinkAuto once everything works.
 	nuxiinit();
 
 	flagcount("1", "use alternate profiling code", &debug['1']);
@@ -122,6 +123,10 @@ main(int argc, char *argv[])
 	flagcount("shared", "generate shared object", &flag_shared);
 	
 	flagparse(&argc, &argv, usage);
+	
+	// TODO: link mode flag instead of isobj
+	if(isobj)
+		linkmode = LinkExternal;
 
 	if(argc != 1)
 		usage();
@@ -282,6 +287,7 @@ main(int argc, char *argv[])
 	reloc();
 	asmb();
 	undef();
+	hostlink();
 	if(debug['v']) {
 		Bprint(&bso, "%5.2f cpu time\n", cputime());
 		Bprint(&bso, "%d symbols\n", nsymbol);