cmd/gc: replace '·' as '.' in ELF/Mach-O symbol tables

Old versions of DTrace (as those shipped in OS X and FreeBSD)
don't support unicode characters in symbol names.  Replace '·'
to '.' to make DTrace happy.

Fixes #7493

LGTM=aram, rsc
R=aram, rsc, gobot, iant
CC=golang-codereviews
https://golang.org/cl/72280043

src/cmd/ld/macho.c

@@ -574,6 +574,7 @@ machosymtab(void)
 {
 	int i;
 	LSym *symtab, *symstr, *s, *o;
+	char *p;
 
 	symtab = linklookup(ctxt, ".machosymtab", 0);
 	symstr = linklookup(ctxt, ".machosymstr", 0);
@@ -585,7 +586,21 @@ machosymtab(void)
 		// Only add _ to C symbols. Go symbols have dot in the name.
 		if(strstr(s->extname, ".") == nil)
 			adduint8(ctxt, symstr, '_');
-		addstring(symstr, s->extname);
+		// replace "·" as ".", because DTrace cannot handle it.
+		if(strstr(s->extname, "·") == nil) {
+			addstring(symstr, s->extname);
+		} else {
+			p = s->extname;
+			while (*p++ != '\0') {
+				if(*p == '\xc2' && *(p+1) == '\xb7') {
+					adduint8(ctxt, symstr, '.');
+					p++;
+				} else {
+					adduint8(ctxt, symstr, *p);
+				}
+			}
+			adduint8(ctxt, symstr, '\0');
+		}
 		if(s->type == SDYNIMPORT || s->type == SHOSTOBJ) {
 			adduint8(ctxt, symtab, 0x01); // type N_EXT, external symbol
 			adduint8(ctxt, symtab, 0); // no section

src/cmd/ld/symtab.c

@@ -40,6 +40,7 @@ static int
 putelfstr(char *s)
 {
 	int off, n;
+	char *p, *q;
 
 	if(elfstrsize == 0 && s[0] != 0) {
 		// first entry must be empty string
@@ -54,6 +55,21 @@ putelfstr(char *s)
 	off = elfstrsize;
 	elfstrsize += n;
 	memmove(elfstrdat+off, s, n);
+	// replace "·" as ".", because DTrace cannot handle it.
+	p = strstr(s, "·");
+	if(p != nil) {
+		p = q = elfstrdat+off;
+		while (*q != '\0') {
+			if(*q == '\xc2' && *(q+1) == '\xb7') {
+				q += 2;
+				*p++ = '.';
+				elfstrsize--;
+			} else {
+				*p++ = *q++;
+			}
+		}
+		*p = '\0';
+	}
 	return off;
 }