cmd/nm: make -S listing a bit more accurate

Hide container symbols like text and etext so that
the individual pieces inside are shown instead.
For example, if text and main.init have the same
address, it was a toss-up which name was printed.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/13722046

src/cmd/nm/nm.c

@@ -299,6 +299,37 @@ psym(Sym *s, void* p)
 	symptr[nsym++] = s;
 }
 
+const char *skipnames[] = {
+	"bss",
+	"data",
+	"ebss",
+	"edata",
+	"egcbss",
+	"egcdata",
+	"enoptrbss",
+	"enoptrdata",
+	"epclntab",
+	"erodata",
+	"esymtab",
+	"etext",
+	"etypelink",
+	"noptrbss",
+	"noptrdata",
+	"rodata",
+	"text",
+};
+
+int
+skipsize(char *name)
+{
+	int i;
+	
+	for(i=0; i<nelem(skipnames); i++)
+		if(strcmp(skipnames[i], name) == 0)
+			return 1;
+	return 0;
+}
+
 void
 printsyms(Sym **symptr, long nsym)
 {
@@ -332,12 +363,12 @@ printsyms(Sym **symptr, long nsym)
 			Bprint(&bout, "%*llux ", wid, s->value);
 		else
 			Bprint(&bout, "%*s ", wid, "");
-		if(Sflag) {
+		if(Sflag && !skipsize(cp)) {
 			vlong siz;
 
 			siz = 0;
 			for(j=i+1; j<nsym; j++) {
-				if(symptr[j]->type != 'a' && symptr[j]->type != 'p') {
+				if(!skipsize(symptr[j]->name) && symptr[j]->type != 'a' && symptr[j]->type != 'p') {
 					siz = symptr[j]->value - s->value;
 					break;
 				}