cmd/ld: move instruction selection + layout into compilers, assemblers

- new object file reader/writer (liblink/objfile.c)
- remove old object file writing routines
- add pcdata iterator
- remove all trace of "line number stack" and "path fragments" from
  object files, linker (!!!)
- dwarf now writes a single "compilation unit" instead of one per package

This CL disables the check for chains of no-split functions that
could overflow the stack red zone. A future CL will attack the problem
of reenabling that check (issue 6931).

This CL is just the liblink and cmd/ld changes.
There are minor associated adjustments in CL 37030045.
Each depends on the other.

R=golang-dev, dave, iant
CC=golang-dev
https://codereview.appspot.com/39680043

1 files changed, 11 insertions, 329 deletions

diff --git a/src/liblink/ld.c b/src/liblink/ld.c
index f6632877b..1d06f809a 100644
--- a/src/liblink/ld.c
+++ b/src/liblink/ld.c
@@ -35,329 +35,14 @@
 #include <link.h>
 
 void
-copyhistfrog(Link *ctxt, char *buf, int nbuf)
+addlib(Link *ctxt, char *src, char *obj, char *pathname)
 {
-	char *p, *ep;
+	char name[1024], pname[1024], *p;
 	int i;
 
-	p = buf;
-	ep = buf + nbuf;
-	for(i=0; i<ctxt->histfrogp; i++) {
-		p = seprint(p, ep, "%s", ctxt->histfrog[i]->name+1);
-		if(i+1<ctxt->histfrogp && (p == buf || p[-1] != '/'))
-			p = seprint(p, ep, "/");
-	}
-}
-
-void
-addhist(Link *ctxt, int32 line, int type)
-{
-	Auto *u;
-	LSym *s;
-	int i, j, k;
-
-	u = emallocz(sizeof(Auto));
-	s = emallocz(sizeof(LSym));
-	s->name = emallocz(2*(ctxt->histfrogp+1) + 1);
-
-	u->asym = s;
-	u->type = type;
-	u->aoffset = line;
-	u->link = ctxt->curhist;
-	ctxt->curhist = u;
-
-	s->name[0] = 0;
-	j = 1;
-	for(i=0; i<ctxt->histfrogp; i++) {
-		k = ctxt->histfrog[i]->value;
-		s->name[j+0] = k>>8;
-		s->name[j+1] = k;
-		j += 2;
-	}
-	s->name[j] = 0;
-	s->name[j+1] = 0;
-}
-
-void
-histtoauto(Link *ctxt)
-{
-	Auto *l;
-
-	while(l = ctxt->curhist) {
-		ctxt->curhist = l->link;
-		l->link = ctxt->curauto;
-		ctxt->curauto = l;
-	}
-}
-
-void
-collapsefrog(Link *ctxt, LSym *s)
-{
-	int i;
-
-	/*
-	 * bad encoding of path components only allows
-	 * MAXHIST components. if there is an overflow,
-	 * first try to collapse xxx/..
-	 */
-	for(i=1; i<ctxt->histfrogp; i++)
-		if(strcmp(ctxt->histfrog[i]->name+1, "..") == 0) {
-			memmove(ctxt->histfrog+i-1, ctxt->histfrog+i+1,
-				(ctxt->histfrogp-i-1)*sizeof(ctxt->histfrog[0]));
-			ctxt->histfrogp--;
-			goto out;
-		}
-
-	/*
-	 * next try to collapse .
-	 */
-	for(i=0; i<ctxt->histfrogp; i++)
-		if(strcmp(ctxt->histfrog[i]->name+1, ".") == 0) {
-			memmove(ctxt->histfrog+i, ctxt->histfrog+i+1,
-				(ctxt->histfrogp-i-1)*sizeof(ctxt->histfrog[0]));
-			goto out;
-		}
-
-	/*
-	 * last chance, just truncate from front
-	 */
-	memmove(ctxt->histfrog+0, ctxt->histfrog+1,
-		(ctxt->histfrogp-1)*sizeof(ctxt->histfrog[0]));
-
-out:
-	ctxt->histfrog[ctxt->histfrogp-1] = s;
-}
-
-// Saved history stacks encountered while reading archives.
-// Keeping them allows us to answer virtual lineno -> file:line
-// queries.
-//
-// The history stack is a complex data structure, described best at the
-// bottom of http://plan9.bell-labs.com/magic/man2html/6/a.out.
-// One of the key benefits of interpreting it here is that the runtime
-// does not have to. Perhaps some day the compilers could generate
-// a simpler linker input too.
-
-// savehist processes a single line, off history directive
-// found in the input object file.
-void
-savehist(Link *ctxt, int32 line, int32 off)
-{
-	char tmp[1024];
-	LSym *file;
-	Hist2 *h;
-
-	// NOTE(rsc): We used to do the copyctxt->histfrog first and this
-	// condition was if(tmp[0] != '\0') to check for an empty string,
-	// implying that ctxt->histfrogp == 0, implying that this is a history pop.
-	// However, on Windows in the misc/cgo test, the linker is
-	// presented with an ANAME corresponding to an empty string,
-	// that ANAME ends up being the only ctxt->histfrog, and thus we have
-	// a situation where ctxt->histfrogp > 0 (not a pop) but the path we find
-	// is the empty string. Really that shouldn't happen, but it doesn't
-	// seem to be bothering anyone yet, and it's easier to fix the condition
-	// to test ctxt->histfrogp than to track down where that empty string is
-	// coming from. Probably it is coming from go tool pack's P command.
-	if(ctxt->histfrogp > 0) {
-		tmp[0] = '\0';
-		copyhistfrog(ctxt, tmp, sizeof tmp);
-		file = linklookup(ctxt, tmp, HistVersion);
-	} else
-		file = nil;
-
-	if(file != nil && line == 1 && off == 0) {
-		// start of new stack
-		if(ctxt->histdepth != 0)
-			sysfatal("history stack phase error: unexpected start of new stack depth=%d file=%s", ctxt->histdepth, tmp);
-		ctxt->nhist2 = 0;
-		ctxt->histcopy = nil;
-	}
-	
-	if(ctxt->nhist2 >= ctxt->maxhist2) {
-		if(ctxt->maxhist2 == 0)
-			ctxt->maxhist2 = 1;
-		ctxt->maxhist2 *= 2;
-		ctxt->hist2 = erealloc(ctxt->hist2, ctxt->maxhist2*sizeof ctxt->hist2[0]);
-	}
-	h = &ctxt->hist2[ctxt->nhist2++];
-	h->line = line;
-	h->off = off;
-	h->file = file;
-	
-	if(file != nil) {
-		if(off == 0)
-			ctxt->histdepth++;
-	} else {
-		if(off != 0)
-			sysfatal("history stack phase error: bad offset in pop");
-		ctxt->histdepth--;
-	}
-}
-
-// gethist returns the history stack currently in effect.
-// The result is valid indefinitely.
-Hist2*
-gethist(Link *ctxt)
-{
-	if(ctxt->histcopy == nil) {
-		if(ctxt->nhist2 == 0)
-			return nil;
-		ctxt->histcopy = emallocz((ctxt->nhist2+1)*sizeof ctxt->hist2[0]);
-		memmove(ctxt->histcopy, ctxt->hist2, ctxt->nhist2*sizeof ctxt->hist2[0]);
-		ctxt->histcopy[ctxt->nhist2].line = -1;
-	}
-	return ctxt->histcopy;
-}
-
-typedef struct Hstack Hstack;
-struct Hstack
-{
-	Hist2 *h;
-	int delta;
-};
-
-// getline sets *f to the file number and *l to the line number
-// of the virtual line number line according to the history stack h.
-void
-linkgetline(Link *ctxt, Hist2 *h, int32 line, LSym **f, int32 *l)
-{
-	Hstack stk[100];
-	int nstk, start;
-	Hist2 *top, *h0;
-	static Hist2 *lasth;
-	static int32 laststart, lastend, lastdelta;
-	static LSym *lastfile;
-
-	h0 = h;
-	*f = 0;
-	*l = 0;
-	start = 0;
-	if(h == nil || line == 0) {
-		print("%s: getline: h=%p line=%d\n", ctxt->cursym->name, h, line);
-		return;
-	}
-
-	// Cache span used during last lookup, so that sequential
-	// translation of line numbers in compiled code is efficient.
-	if(!ctxt->debughist && lasth == h && laststart <= line && line < lastend) {
-		*f = lastfile;
-		*l = line - lastdelta;
-		return;
-	}
-
-	if(ctxt->debughist)
-		print("getline %d laststart=%d lastend=%d\n", line, laststart, lastend);
-	
-	nstk = 0;
-	for(; h->line != -1; h++) {
-		if(ctxt->debughist)
-			print("\t%s %d %d\n", h->file ? h->file->name : "?", h->line, h->off);
-
-		if(h->line > line) {
-			if(nstk == 0)
-				sysfatal("history stack phase error: empty stack at line %d", (int)line);
-			top = stk[nstk-1].h;
-			lasth = h;
-			lastfile = top->file;
-			laststart = start;
-			lastend = h->line;
-			lastdelta = stk[nstk-1].delta;
-			*f = lastfile;
-			*l = line - lastdelta;
-			if(ctxt->debughist)
-				print("\tgot %d %d [%d %d %d]\n", *f, *l, laststart, lastend, lastdelta);
-			return;
-		}
-		if(h->file == nil) {
-			// pop included file
-			if(nstk == 0)
-				sysfatal("history stack phase error: stack underflow");
-			nstk--;
-			if(nstk > 0)
-				stk[nstk-1].delta += h->line - stk[nstk].h->line;
-			start = h->line;
-		} else if(h->off == 0) {
-			// push included file
-			if(nstk >= nelem(stk))
-				sysfatal("history stack phase error: stack overflow");
-			start = h->line;
-			stk[nstk].h = h;
-			stk[nstk].delta = h->line - 1;
-			nstk++;
-		} else {
-			// #line directive
-			if(nstk == 0)
-				sysfatal("history stack phase error: stack underflow");
-			stk[nstk-1].h = h;
-			stk[nstk-1].delta = h->line - h->off;
-			start = h->line;
-		}
-		if(ctxt->debughist)
-			print("\t\tnstk=%d delta=%d\n", nstk, stk[nstk].delta);
-	}
-
-	sysfatal("history stack phase error: cannot find line for %d", line);
-	nstk = 0;
-	for(h = h0; h->line != -1; h++) {
-		print("\t%d %d %s\n", h->line, h->off, h->file ? h->file->name : "");
-		if(h->file == nil)
-			nstk--;
-		else if(h->off == 0)
-			nstk++;
-	}
-}
-
-void
-addlib(Link *ctxt, char *src, char *obj)
-{
-	char name[1024], pname[1024], comp[256], *p;
-	int i, search;
-
-	if(ctxt->histfrogp <= 0)
-		return;
-
-	search = 0;
-	if(ctxt->histfrog[0]->name[1] == '/') {
-		sprint(name, "");
-		i = 1;
-	} else
-	if(isalpha((uchar)ctxt->histfrog[0]->name[1]) && ctxt->histfrog[0]->name[2] == ':') {
-		strcpy(name, ctxt->histfrog[0]->name+1);
-		i = 1;
-	} else
-	if(ctxt->histfrog[0]->name[1] == '.') {
-		sprint(name, ".");
-		i = 0;
-	} else {
-		sprint(name, "");
-		i = 0;
-		search = 1;
-	}
-
-	for(; i<ctxt->histfrogp; i++) {
-		snprint(comp, sizeof comp, "%s", ctxt->histfrog[i]->name+1);
-		for(;;) {
-			p = strstr(comp, "$O");
-			if(p == 0)
-				break;
-			memmove(p+1, p+2, strlen(p+2)+1);
-			p[0] = ctxt->thechar;
-		}
-		for(;;) {
-			p = strstr(comp, "$M");
-			if(p == 0)
-				break;
-			if(strlen(comp)+strlen(ctxt->thestring)-2+1 >= sizeof comp)
-				sysfatal("library component too long");
-			memmove(p+strlen(ctxt->thestring), p+2, strlen(p+2)+1);
-			memmove(p, ctxt->thestring, strlen(ctxt->thestring));
-		}
-		if(strlen(name) + strlen(comp) + 3 >= sizeof(name))
-			sysfatal("library component too long");
-		if(i > 0 || !search)
-			strcat(name, "/");
-		strcat(name, comp);
-	}
+	if(strlen(pathname) >= sizeof name)
+		sysfatal("addlib pathname too long");
+	strcpy(name, pathname);
 	cleanname(name);
 	
 	// runtime.a -> runtime
@@ -376,15 +61,12 @@ addlib(Link *ctxt, char *src, char *obj)
 	if(p != nil)
 		*p = '.';
 
-	if(search) {
-		// try dot, -L "libdir", and then goroot.
-		for(i=0; i<ctxt->nlibdir; i++) {
-			snprint(pname, sizeof pname, "%s/%s", ctxt->libdir[i], name);
-			if(access(pname, AEXIST) >= 0)
-				break;
-		}
-	}else
-		strcpy(pname, name);
+	// try dot, -L "libdir", and then goroot.
+	for(i=0; i<ctxt->nlibdir; i++) {
+		snprint(pname, sizeof pname, "%s/%s", ctxt->libdir[i], name);
+		if(access(pname, AEXIST) >= 0)
+			break;
+	}
 	cleanname(pname);
 
 	/* runtime.a -> runtime */