liblink: support big-endian properly

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/115300044

include/link.h

@@ -431,11 +431,17 @@ struct	Link
 	LSym*	filesyms;
 };
 
+enum {
+	LittleEndian = 0x04030201,
+	BigEndian = 0x01020304,
+};
+
 // LinkArch is the definition of a single architecture.
 struct LinkArch
 {
 	char*	name; // "arm", "amd64", and so on
 	int	thechar;	// '5', '6', and so on
+	int32	endian; // LittleEndian or BigEndian
 
 	void	(*addstacksplit)(Link*, LSym*);
 	void	(*assemble)(Link*, LSym*);
@@ -560,7 +566,7 @@ int	find1(int32 l, int c);
 void	linkgetline(Link *ctxt, int32 line, LSym **f, int32 *l);
 void	histtoauto(Link *ctxt);
 void	mkfwd(LSym*);
-void	nuxiinit(void);
+void	nuxiinit(LinkArch*);
 void	savehist(Link *ctxt, int32 line, int32 off);
 Prog*	copyp(Link*, Prog*);
 Prog*	appendp(Link*, Prog*);

src/liblink/ld.c

@@ -130,16 +130,26 @@ find1(int32 l, int c)
 }
 
 void
-nuxiinit(void)
+nuxiinit(LinkArch *arch)
 {
 	int i, c;
 
+	if(arch->endian != BigEndian && arch->endian != LittleEndian)
+		sysfatal("unknown endian (%#x) for arch %s", arch->endian, arch->name);
+
 	for(i=0; i<4; i++) {
-		c = find1(0x04030201L, i+1);
-		if(i < 2)
-			inuxi2[i] = c;
-		if(i < 1)
-			inuxi1[i] = c;
+		c = find1(arch->endian, i+1);
+		if(arch->endian == LittleEndian) {
+			if(i < 2)
+				inuxi2[i] = c;
+			if(i < 1)
+				inuxi1[i] = c;
+		} else {
+			if(i >= 2)
+				inuxi2[i-2] = c;
+			if(i >= 3)
+				inuxi1[i-3] = c;
+		}
 		inuxi4[i] = c;
 		if(c == i) {
 			inuxi8[i] = c;
@@ -149,8 +159,13 @@ nuxiinit(void)
 			inuxi8[i+4] = c;
 		}
 		fnuxi4[i] = c;
-		fnuxi8[i] = c;
-		fnuxi8[i+4] = c+4;
+		if(c == i) {
+			fnuxi8[i] = c;
+			fnuxi8[i+4] = c+4;
+		} else {
+			fnuxi8[i] = c+4;
+			fnuxi8[i+4] = c;
+		}
 	}
 }
 

src/liblink/obj5.c

@@ -1033,6 +1033,7 @@ loop:
 LinkArch linkarm = {
 	.name = "arm",
 	.thechar = '5',
+	.endian = LittleEndian,
 
 	.addstacksplit = addstacksplit,
 	.assemble = span5,

src/liblink/obj6.c

@@ -1087,6 +1087,7 @@ prg(void)
 LinkArch linkamd64 = {
 	.name = "amd64",
 	.thechar = '6',
+	.endian = LittleEndian,
 
 	.addstacksplit = addstacksplit,
 	.assemble = span6,
@@ -1132,6 +1133,7 @@ LinkArch linkamd64 = {
 LinkArch linkamd64p32 = {
 	.name = "amd64p32",
 	.thechar = '6',
+	.endian = LittleEndian,
 
 	.addstacksplit = addstacksplit,
 	.assemble = span6,

src/liblink/obj8.c

@@ -816,6 +816,7 @@ loop:
 LinkArch link386 = {
 	.name = "386",
 	.thechar = '8',
+	.endian = LittleEndian,
 
 	.addstacksplit = addstacksplit,
 	.assemble = span8,

src/liblink/sym.c

@@ -91,7 +91,7 @@ linknew(LinkArch *arch)
 	char *p;
 	char buf[1024];
 
-	nuxiinit();
+	nuxiinit(arch);
 	
 	ctxt = emallocz(sizeof *ctxt);
 	ctxt->arch = arch;