liblink, cmd/ld: reenable nosplit checking and test

The new code is adapted from the Go 1.2 nosplit code,
but it does not have the bug reported in issue 7623:

g% go run nosplit.go
g% go1.2 run nosplit.go
BUG
rejected incorrectly:
        main 0 call f; f 120

        linker output:
        # _/tmp/go-test-nosplit021064539
        main.main: nosplit stack overflow
                120	guaranteed after split check in main.main
                112	on entry to main.f
                -8	after main.f uses 120

g%

Fixes issue 6931.
Fixes issue 7623.

LGTM=iant
R=golang-codereviews, iant, ality
CC=golang-codereviews, r
https://codereview.appspot.com/88190043

1 files changed, 3 insertions, 2 deletions

diff --git a/src/liblink/pcln.c b/src/liblink/pcln.c
index 62c0e8501..4b2b85543 100644
--- a/src/liblink/pcln.c
+++ b/src/liblink/pcln.c
@@ -347,11 +347,11 @@ pciternext(Pciter *it)
 	
 	// pc delta
 	v = getvarint(&it->p);
-	it->nextpc = it->pc + v;
+	it->nextpc = it->pc + v*it->pcscale;
 }
 
 void
-pciterinit(Pciter *it, Pcdata *d)
+pciterinit(Link *ctxt, Pciter *it, Pcdata *d)
 {
 	it->d = *d;
 	it->p = it->d.p;
@@ -360,5 +360,6 @@ pciterinit(Pciter *it, Pcdata *d)
 	it->value = -1;
 	it->start = 1;
 	it->done = 0;
+	it->pcscale = ctxt->arch->minlc;
 	pciternext(it);
 }