cmd/cc, cmd/ld, runtime: disallow conservative data/bss objects

In linker, refuse to write conservative (array of pointers) as the
garbage collection type for any variable in the data/bss GC program.

In the linker, attach the Go type to an already-read C declaration
during dedup. This gives us Go types for C globals for free as long
as the cmd/dist-generated Go code contains the declaration.
(Most runtime C declarations have a corresponding Go declaration.
Both are bss declarations and so the linker dedups them.)

In cmd/dist, add a few more C files to the auto-Go-declaration list
in order to get Go type information for the C declarations into the linker.

In C compiler, mark all non-pointer-containing global declarations
and all string data as NOPTR. This allows them to exist in C files
without any corresponding Go declaration. Count C function pointers
as "non-pointer-containing", since we have no heap-allocated C functions.

In runtime, add NOPTR to the remaining pointer-containing declarations,
none of which refer to Go heap objects.

In runtime, also move os.Args and syscall.envs data into runtime-owned
variables. Otherwise, in programs that do not import os or syscall, the
runtime variables named os.Args and syscall.envs will be missing type
information.

I believe that this CL eliminates the final source of conservative GC scanning
in non-SWIG Go programs, and therefore...

Fixes #909.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/149770043

1 files changed, 11 insertions, 0 deletions

diff --git a/src/runtime/runtime.go b/src/runtime/runtime.go
index dbaea45a66..4e4e1d17a5 100644
--- a/src/runtime/runtime.go
+++ b/src/runtime/runtime.go
@@ -9,6 +9,8 @@ var ticks struct {
 	val  uint64
 }
 
+var tls0 [8]uintptr // available storage for m0's TLS; not necessarily used; opaque to GC
+
 // Note: Called by runtime/pprof in addition to runtime code.
 func tickspersecond() int64 {
 	r := int64(atomicload64(&ticks.val))
@@ -47,3 +49,12 @@ func parforalloc(nthrmax uint32) *parfor {
 		nthrmax: nthrmax,
 	}
 }
+
+var envs []string
+var argslice []string
+
+// called from syscall
+func runtime_envs() []string { return envs }
+
+// called from os
+func runtime_args() []string { return argslice }