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, 16 insertions, 9 deletions

diff --git a/src/runtime/runtime.c b/src/runtime/runtime.c
index aa8dd8f7a0..b3503fb909 100644
--- a/src/runtime/runtime.c
+++ b/src/runtime/runtime.c
@@ -62,10 +62,12 @@ runtime·mchr(byte *p, byte c, byte *ep)
 }
 
 static int32	argc;
+
+#pragma dataflag NOPTR /* argv not a heap pointer */
 static uint8**	argv;
 
-Slice os·Args;
-Slice syscall·envs;
+extern Slice runtime·argslice;
+extern Slice runtime·envs;
 
 void (*runtime·sysargs)(int32, uint8**);
 
@@ -97,8 +99,8 @@ runtime·goargs(void)
 	if(Windows)
 		return;
 
-	os·Args = runtime·makeStringSlice(argc);
-	s = (String*)os·Args.array;
+	runtime·argslice = runtime·makeStringSlice(argc);
+	s = (String*)runtime·argslice.array;
 	for(i=0; i<argc; i++)
 		s[i] = runtime·gostringnocopy(argv[i]);
 }
@@ -112,8 +114,8 @@ runtime·goenvs_unix(void)
 	for(n=0; argv[argc+1+n] != 0; n++)
 		;
 
-	syscall·envs = runtime·makeStringSlice(n);
-	s = (String*)syscall·envs.array;
+	runtime·envs = runtime·makeStringSlice(n);
+	s = (String*)runtime·envs.array;
 	for(i=0; i<n; i++)
 		s[i] = runtime·gostringnocopy(argv[argc+1+i]);
 }
@@ -122,7 +124,7 @@ runtime·goenvs_unix(void)
 Slice
 runtime·environ()
 {
-	return syscall·envs;
+	return runtime·envs;
 }
 
 int32
@@ -267,10 +269,15 @@ runtime·check(void)
 #pragma dataflag NOPTR
 DebugVars	runtime·debug;
 
-static struct {
+typedef struct DbgVar DbgVar;
+struct DbgVar
+{
 	int8*	name;
 	int32*	value;
-} dbgvar[] = {
+};
+
+#pragma dataflag NOPTR /* dbgvar has no heap pointers */
+static DbgVar dbgvar[] = {
 	{"allocfreetrace", &runtime·debug.allocfreetrace},
 	{"efence", &runtime·debug.efence},
 	{"gctrace", &runtime·debug.gctrace},