cmd/dist: goc2c ignores GOROOT_FINAL

When building golang, the environment variable GOROOT_FINAL can be set
to indicate a different installation location from the build
location. This works fine, except that the goc2c build step embeds
line numbers in the resulting c source files that refer to the build
location, no the install location.

This would not be a big deal, except that in turn the linker uses the
location of runtime/string.goc to embed the gdb script in the
resulting binary and as a net result, the debugger now complains that
the script is outside its load path (it has the install location
configured).

See https://code.google.com/p/go/issues/detail?id=8524 for the full
description.

Fixes #8524.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/128230046

src/cmd/dist/a.h

@@ -109,7 +109,7 @@ void	mkzexperiment(char*, char*);
 void	mkzdefaultcc(char*, char*);
 
 // goc2c.c
-void	goc2c(char*, char*);
+void	goc2c(char*, char*, char*);
 
 // main.c
 extern int vflag;

src/cmd/dist/build.c

@@ -640,7 +640,7 @@ install(char *dir)
 {
 	char *name, *p, *elem, *prefix, *exe;
 	bool islib, ispkg, isgo, stale, ispackcmd;
-	Buf b, b1, path;
+	Buf b, b1, path, final_path, final_name;
 	Vec compile, files, link, go, missing, clean, lib, extra;
 	Time ttarg, t;
 	int i, j, k, n, doclean, targ;
@@ -655,6 +655,8 @@ install(char *dir)
 	binit(&b);
 	binit(&b1);
 	binit(&path);
+	binit(&final_path);
+	binit(&final_name);
 	vinit(&compile);
 	vinit(&files);
 	vinit(&link);
@@ -667,6 +669,7 @@ install(char *dir)
 
 	// path = full path to dir.
 	bpathf(&path, "%s/src/%s", goroot, dir);
+	bpathf(&final_path, "%s/src/%s", goroot_final, dir);
 	name = lastelem(dir);
 
 	// For misc/prof, copy into the tool directory and we're done.
@@ -939,9 +942,10 @@ install(char *dir)
 				continue;
 			// b = path/zp but with _goos_goarch.c instead of .goc
 			bprintf(&b, "%s%sz%s", bstr(&path), slash, lastelem(p));
+			bprintf(&final_name, "%s%s%s", bstr(&final_path), slash, lastelem(p));
 			b.len -= 4;
 			bwritef(&b, "_%s_%s.c", goos, goarch);
-			goc2c(p, bstr(&b));
+			goc2c(p, bstr(&final_name), bstr(&b));
 			vadd(&files, bstr(&b));
 		}
 		vuniq(&files);

src/cmd/dist/goc2c.c

@@ -66,6 +66,7 @@ static int gcc;
 
 /* File and line number */
 static const char *file;
+static const char *final_file;
 static unsigned int lineno;
 
 /* List of names and types.  */
@@ -474,7 +475,7 @@ read_func_header(char **name, struct params **params, int *paramwid, struct para
 			if (lastline == lineno-1)
 				bwritef(output, "\n");
 			else
-				bwritef(output, "\n#line %d \"%s\"\n", lineno, file);
+				bwritef(output, "\n#line %d \"%s\"\n", lineno, final_file);
 			lastline = lineno;
 		}
 		bwritef(output, "%s ", token);
@@ -658,7 +659,7 @@ write_func_header(char *package, char *name,
 		write_gcc_func_header(package, name, params, rets);
 	else
 		write_6g_func_header(package, name, params, paramwid, rets);
-	bwritef(output, "#line %d \"%s\"\n", lineno, file);
+	bwritef(output, "#line %d \"%s\"\n", lineno, final_file);
 }
 
 /* Write out a function trailer.  */
@@ -772,7 +773,7 @@ process_file(void)
 }
 
 void
-goc2c(char *goc, char *c)
+goc2c(char *goc, char *goc_final, char *c)
 {
 	int i;
 	Buf in, out;
@@ -781,6 +782,7 @@ goc2c(char *goc, char *c)
 	binit(&out);
 	
 	file = goc;
+	final_file = goc_final;
 	readfile(&in, goc);
 
 	// TODO: set gcc=1 when using gcc