cmd/ld: diagnose Go calling C

For example:
go build -ldflags -C cmd/go 2>&1 | awk '{print $NF}' | sort | uniq -c | sort -nr

LGTM=khr
R=khr, josharian
CC=golang-codereviews
https://golang.org/cl/135170044

diff --git a/include/link.h b/include/link.h
index 2b4de789d5d11be7d2d29cfaee88e56b77b1c7fc..73f148c14c1fc131efb78e928ccfc8f7499ac870 100644 (file)
--- a/include/link.h
+++ b/include/link.h
@@ -126,6 +126,7 @@ struct      LSym
        short   type;
        short   version;
        uchar   dupok;
+       uchar   cfunc;
        uchar   external;
        uchar   nosplit;
        uchar   reachable;

diff --git a/src/cmd/cc/pgen.c b/src/cmd/cc/pgen.c
index 53410a11a0713da390076183ceb212d9304cf920..99128d40055892495ea5be76351a1ea4d0cdcdcd 100644 (file)
--- a/src/cmd/cc/pgen.c
+++ b/src/cmd/cc/pgen.c
@@ -131,6 +131,7 @@ codgen(Node *n, Node *nn)
        nearln = nn->lineno;
 
        p = gtext(n1->sym, stkoff);
+       p->from.sym->cfunc = 1;
        sp = p;
 
        /*

diff --git a/src/cmd/ld/lib.c b/src/cmd/ld/lib.c
index a68993715dbb26e770a9a237ad7de6341eb09a14..51e10bb99dd8e383001f2ad2c5c02cba8945024d 100644 (file)
--- a/src/cmd/ld/lib.c
+++ b/src/cmd/ld/lib.c
@@ -1554,3 +1554,56 @@ diag(char *fmt, ...)
                errorexit();
        }
 }
+
+void
+checkgo(void)
+{
+       LSym *s;
+       Reloc *r;
+       int i;
+       int changed;
+       
+       if(!debug['C'])
+               return;
+       
+       // TODO(rsc,khr): Eventually we want to get to no Go-called C functions at all,
+       // which would simplify this logic quite a bit.
+
+       // Mark every Go-called C function with cfunc=2, recursively.
+       do {
+               changed = 0;
+               for(s = ctxt->textp; s != nil; s = s->next) {
+                       if(s->cfunc == 0 || (s->cfunc == 2 && s->nosplit)) {
+                               for(i=0; i<s->nr; i++) {
+                                       r = &s->r[i];
+                                       if(r->sym == nil)
+                                               continue;
+                                       if((r->type == R_CALL || r->type == R_CALLARM) && r->sym->type == STEXT) {
+                                               if(r->sym->cfunc == 1) {
+                                                       changed = 1;
+                                                       r->sym->cfunc = 2;
+                                               }
+                                       }
+                               }
+                       }
+               }
+       }while(changed);
+
+       // Complain about Go-called C functions that can split the stack
+       // (that can be preempted for garbage collection or trigger a stack copy).
+       for(s = ctxt->textp; s != nil; s = s->next) {
+               if(s->cfunc == 0 || (s->cfunc == 2 && s->nosplit)) {
+                       for(i=0; i<s->nr; i++) {
+                               r = &s->r[i];
+                               if(r->sym == nil)
+                                       continue;
+                               if((r->type == R_CALL || r->type == R_CALLARM) && r->sym->type == STEXT) {
+                                       if(s->cfunc == 0 && r->sym->cfunc == 2 && !r->sym->nosplit)
+                                               print("Go %s calls C %s\n", s->name, r->sym->name);
+                                       else if(s->cfunc == 2 && s->nosplit && !r->sym->nosplit)
+                                               print("Go calls C %s calls %s\n", s->name, r->sym->name);
+                               }
+                       }
+               }
+       }
+}

diff --git a/src/cmd/ld/lib.h b/src/cmd/ld/lib.h
index dd2399023472c544dc8eabdbaea8f6a23b770d6f..067ffa0bcc4f8a260deff0346a22d35e3e8ff040 100644 (file)
--- a/src/cmd/ld/lib.h
+++ b/src/cmd/ld/lib.h
@@ -183,6 +183,7 @@ uint16      be16(uchar *b);
 uint32 be32(uchar *b);
 uint64 be64(uchar *b);
 void   callgraph(void);
+void   checkgo(void);
 void   cflush(void);
 void   codeblk(int64 addr, int64 size);
 vlong  cpos(void);

diff --git a/src/cmd/ld/pobj.c b/src/cmd/ld/pobj.c
index d78dacd3683d8b65dbb3203b115ac7cfa527cb27..54c5ef247281e84f0b53102d212031c11cf76eaf 100644 (file)
--- a/src/cmd/ld/pobj.c
+++ b/src/cmd/ld/pobj.c
@@ -71,6 +71,7 @@ main(int argc, char *argv[])
        if(thechar == '6')
                flagcount("8", "assume 64-bit addresses", &debug['8']);
        flagfn1("B", "info: define ELF NT_GNU_BUILD_ID note", addbuildinfo);
+       flagcount("C", "check Go calls to C code", &debug['C']);
        flagint64("D", "addr: data address", &INITDAT);
        flagstr("E", "sym: entry symbol", &INITENTRY);
        if(thechar == '5')
@@ -162,6 +163,7 @@ main(int argc, char *argv[])
                mark(linklookup(ctxt, "runtime.read_tls_fallback", 0));
        }
 
+       checkgo();
        deadcode();
        callgraph();
        paramspace = "SP";      /* (FP) now (SP) on output */

diff --git a/src/liblink/objfile.c b/src/liblink/objfile.c
index 22c9199d5e13bfe2ac23811a4eaae6db7ac9d18a..dc463d474e274bffb92b18915fd714dea68cb588 100644 (file)
--- a/src/liblink/objfile.c
+++ b/src/liblink/objfile.c
@@ -38,7 +38,8 @@
 //     - type [int]
 //     - name [string]
 //     - version [int]
-//     - dupok [int]
+//     - flags [int]
+//             1 dupok
 //     - size [int]
 //     - gotype [symbol reference]
 //     - p [data block]
@@ -50,7 +51,9 @@
 //     - args [int]
 //     - locals [int]
 //     - nosplit [int]
-//     - leaf [int]
+//     - flags [int]
+//             1 leaf
+//             2 C function
 //     - nlocal [int]
 //     - local [nlocal automatics]
 //     - pcln [pcln table]
@@ -289,6 +292,8 @@ writesym(Link *ctxt, Biobuf *b, LSym *s)
                        Bprint(ctxt->bso, "t=%d ", s->type);
                if(s->dupok)
                        Bprint(ctxt->bso, "dupok ");
+               if(s->cfunc)
+                       Bprint(ctxt->bso, "cfunc ");
                if(s->nosplit)
                        Bprint(ctxt->bso, "nosplit ");
                Bprint(ctxt->bso, "size=%lld value=%lld", (vlong)s->size, (vlong)s->value);
@@ -351,7 +356,7 @@ writesym(Link *ctxt, Biobuf *b, LSym *s)
                wrint(b, s->args);
                wrint(b, s->locals);
                wrint(b, s->nosplit);
-               wrint(b, s->leaf);
+               wrint(b, s->leaf | s->cfunc<<1);
                n = 0;
                for(a = s->autom; a != nil; a = a->link)
                        n++;
@@ -519,6 +524,7 @@ readsym(Link *ctxt, Biobuf *f, char *pkg, char *pn)
        if(v != 0 && v != 1)
                sysfatal("invalid symbol version %d", v);
        dupok = rdint(f);
+       dupok &= 1;
        size = rdint(f);
        
        if(v != 0)
@@ -573,7 +579,9 @@ readsym(Link *ctxt, Biobuf *f, char *pkg, char *pn)
                s->args = rdint(f);
                s->locals = rdint(f);
                s->nosplit = rdint(f);
-               s->leaf = rdint(f);
+               v = rdint(f);
+               s->leaf = v&1;
+               s->cfunc = v&2;
                n = rdint(f);
                for(i=0; i<n; i++) {
                        a = emallocz(sizeof *a);
@@ -629,6 +637,8 @@ readsym(Link *ctxt, Biobuf *f, char *pkg, char *pn)
                        Bprint(ctxt->bso, "t=%d ", s->type);
                if(s->dupok)
                        Bprint(ctxt->bso, "dupok ");
+               if(s->cfunc)
+                       Bprint(ctxt->bso, "cfunc ");
                if(s->nosplit)
                        Bprint(ctxt->bso, "nosplit ");
                Bprint(ctxt->bso, "size=%lld value=%lld", (vlong)s->size, (vlong)s->value);

diff --git a/src/pkg/debug/goobj/read.go b/src/pkg/debug/goobj/read.go
index c95fe1e47f3e567755f62f07fa5ab1ce9a912a2a..79a83e59a61caa957d86883dfdc9f521014da9d0 100644 (file)
--- a/src/pkg/debug/goobj/read.go
+++ b/src/pkg/debug/goobj/read.go
@@ -602,7 +602,8 @@ func (r *objReader) parseObject(prefix []byte) error {
                s := &Sym{SymID: r.readSymID()}
                r.p.Syms = append(r.p.Syms, s)
                s.Kind = SymKind(typ)
-               s.DupOK = r.readInt() != 0
+               flags := r.readInt()
+               s.DupOK = flags&1 != 0
                s.Size = r.readInt()
                s.Type = r.readSymID()
                s.Data = r.readData()
@@ -623,7 +624,8 @@ func (r *objReader) parseObject(prefix []byte) error {
                        s.Func = f
                        f.Args = r.readInt()
                        f.Frame = r.readInt()
-                       f.Leaf = r.readInt() != 0
+                       flags := r.readInt()
+                       f.Leaf = flags&1 != 0
                        f.NoSplit = r.readInt() != 0
                        f.Var = make([]Var, r.readInt())
                        for i := range f.Var {