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, 8 insertions, 9 deletions

diff --git a/src/liblink/pass.c b/src/liblink/pass.c
index ed2774991..bc8eb4367 100644
--- a/src/liblink/pass.c
+++ b/src/liblink/pass.c
@@ -70,23 +70,21 @@ linkpatch(Link *ctxt, LSym *sym)
 {
 	int32 c;
 	Prog *p, *q;
-	LSym *s;
 
 	ctxt->cursym = sym;
 	
 	for(p = sym->text; p != nil; p = p->link) {
 		if(ctxt->arch->progedit)
 			ctxt->arch->progedit(ctxt, p);
-		if(p->as == ctxt->arch->ACALL || (p->as == ctxt->arch->AJMP && p->to.type != ctxt->arch->D_BRANCH) || (p->as == ctxt->arch->ARET && p->to.sym != nil)) {
-			s = p->to.sym;
-			// The STEXT check avoids rewriting indirect call to addr in memory on x86.
-			if(s && s->type == STEXT) {
-				p->to.type = ctxt->arch->D_BRANCH;
-				continue;
-			}
-		}
 		if(p->to.type != ctxt->arch->D_BRANCH)
 			continue;
+		if(p->to.u.branch != nil) {
+			// TODO: Remove to.u.branch in favor of p->pcond.
+			p->pcond = p->to.u.branch;
+			continue;
+		}
+		if(p->to.sym != nil)
+			continue;
 		c = p->to.offset;
 		for(q = sym->text; q != nil;) {
 			if(c == q->pc)
@@ -101,6 +99,7 @@ linkpatch(Link *ctxt, LSym *sym)
 				c, p, p->to.sym ? p->to.sym->name : "<nil>");
 			p->to.type = ctxt->arch->D_NONE;
 		}
+		p->to.u.branch = q;
 		p->pcond = q;
 	}