cmd/ld: support for relocation variants

Most ppc64 relocations come in six or more variants where the basic
relocation formula is the same, but which bits of the computed value
are installed where changes.  Introduce the concept of "variants" for
internal relocations to support this.  Since this applies to
architecture-independent relocation types like R_PCREL, we do this in
relocsym.

Currently there is only an identity variant.  A later CL that adds
support for ppc64 ELF relocations will introduce more.

Change-Id: I0c5f0e7dbe5beece79cd24fe36267d37c52f1a0c
Reviewed-on: https://go-review.googlesource.com/2005
Reviewed-by: Russ Cox <rsc@golang.org>

include/link.h

@@ -77,6 +77,7 @@ struct	Reloc
 	uchar	siz;
 	uchar	done;
 	int32	type;
+	int32	variant; // RV_*: variant on computed value
 	int64	add;
 	int64	xadd;
 	LSym*	sym;
@@ -257,6 +258,12 @@ enum
 	R_USEFIELD,
 };
 
+// Reloc.variant
+enum
+{
+	RV_NONE,		// identity variant
+};
+
 // Auto.type
 enum
 {

src/cmd/5l/asm.c

@@ -371,6 +371,15 @@ archreloc(Reloc *r, LSym *s, vlong *val)
 	return -1;
 }
 
+vlong
+archrelocvariant(Reloc *r, LSym *s, vlong t)
+{
+	USED(r);
+	USED(s);
+	sysfatal("unexpected relocation variant");
+	return t;
+}
+
 static Reloc *
 addpltreloc(Link *ctxt, LSym *plt, LSym *got, LSym *sym, int typ)
 {

src/cmd/5l/l.h

@@ -83,6 +83,7 @@ void	adddynrel(LSym *s, Reloc *r);
 void	adddynrela(LSym *rel, LSym *s, Reloc *r);
 void	adddynsym(Link *ctxt, LSym *s);
 int	archreloc(Reloc *r, LSym *s, vlong *val);
+vlong	archrelocvariant(Reloc *r, LSym *s, vlong t);
 void	asmb(void);
 int	elfreloc1(Reloc *r, vlong sectoff);
 void	elfsetupplt(void);

src/cmd/6l/asm.c

@@ -396,6 +396,15 @@ archreloc(Reloc *r, LSym *s, vlong *val)
 	return -1;
 }
 
+vlong
+archrelocvariant(Reloc *r, LSym *s, vlong t)
+{
+	USED(r);
+	USED(s);
+	sysfatal("unexpected relocation variant");
+	return t;
+}
+
 void
 elfsetupplt(void)
 {

src/cmd/6l/l.h

@@ -90,6 +90,7 @@ void	adddynrel(LSym *s, Reloc *r);
 void	adddynrela(LSym *rela, LSym *s, Reloc *r);
 void	adddynsym(Link *ctxt, LSym *s);
 int	archreloc(Reloc *r, LSym *s, vlong *val);
+vlong	archrelocvariant(Reloc *r, LSym *s, vlong t);
 void	asmb(void);
 int	elfreloc1(Reloc *r, vlong sectoff);
 void	elfsetupplt(void);

src/cmd/8l/asm.c

@@ -364,6 +364,15 @@ archreloc(Reloc *r, LSym *s, vlong *val)
 	return -1;
 }
 
+vlong
+archrelocvariant(Reloc *r, LSym *s, vlong t)
+{
+	USED(r);
+	USED(s);
+	sysfatal("unexpected relocation variant");
+	return t;
+}
+
 void
 elfsetupplt(void)
 {

src/cmd/8l/l.h

@@ -74,6 +74,7 @@ void	adddynrel(LSym *s, Reloc *r);
 void	adddynrela(LSym *rela, LSym *s, Reloc *r);
 void	adddynsym(Link *ctxt, LSym *s);
 int	archreloc(Reloc *r, LSym *s, vlong *val);
+vlong	archrelocvariant(Reloc *r, LSym *s, vlong t);
 void	asmb(void);
 int	elfreloc1(Reloc *r, vlong sectoff);
 void	elfsetupplt(void);

src/cmd/9l/asm.c

@@ -177,6 +177,15 @@ archreloc(Reloc *r, LSym *s, vlong *val)
 	return -1;
 }
 
+vlong
+archrelocvariant(Reloc *r, LSym *s, vlong t)
+{
+	USED(r);
+	USED(s);
+	sysfatal("unexpected relocation variant");
+	return t;
+}
+
 void
 adddynsym(Link *ctxt, LSym *s)
 {

src/cmd/9l/l.h

@@ -86,6 +86,7 @@ void	adddynlib(char *lib);
 void	adddynrel(LSym *s, Reloc *r);
 void	adddynsym(Link *ctxt, LSym *s);
 int	archreloc(Reloc *r, LSym *s, vlong *val);
+vlong	archrelocvariant(Reloc *r, LSym *s, vlong t);
 void	listinit(void);
 vlong	rnd(vlong, int32);
 

src/cmd/ld/data.c

@@ -309,6 +309,8 @@ relocsym(LSym *s)
 			o = r->sym->size + r->add;
 			break;
 		}
+		if(r->variant != RV_NONE)
+			o = archrelocvariant(r, s, o);
 //print("relocate %s %#llux (%#llux+%#llux, size %d) => %s %#llux +%#llx [%llx]\n", s->name, (uvlong)(s->value+off), (uvlong)s->value, (uvlong)r->off, r->siz, r->sym ? r->sym->name : "<nil>", (uvlong)symaddr(r->sym), (vlong)r->add, (vlong)o);
 		switch(siz) {
 		default: