Use /proc/self/exe to detect colm build directory

The canonical identity of a file on Unix is the combination of device
and inode numbers. This code checks both possible paths for the
colm executable: directly in the build directory (when colm is linked
against libcolm statically) or in libtool's `objdir` subdirectory (when
colm is linked against libcolm dynamically).

This fails in two situations I can see: when /proc is not mounted or
doesn't exist, or when colm is installed using a hard link.

Author: viccie30

Diff for: src/Makefile.am

@@ -54,7 +54,8 @@ common_CFLAGS = \
 	-Wall \
 	-DINCLUDEDIR='"$(includedir)"' \
 	-DLIBDIR='"$(libdir)"' \
-	-DABS_TOP_BUILDDIR='"$(abs_top_builddir)"'
+	-DABS_TOP_BUILDDIR='"$(abs_top_builddir)"' \
+	-DABS_BUILDDIR='"$(abs_builddir)"'
 
 libprog_a_SOURCES = \
 	buffer.h bytecode.h colm.h debug.h dotgen.h fsmcodegen.h fsmgraph.h \
@@ -214,4 +215,3 @@ colm-wrap: colm-wrap.sh
 loadinit.cc: gen/if1.h
 loadboot2.cc: gen/if2.h
 loadcolm.cc: gen/if3.h
-

Diff for: src/main.cc

@@ -688,14 +688,23 @@ void defaultBuildDir()
 	if ( buildDir != 0 )
 		return;
 
-	const char *ldlp = getenv("LD_LIBRARY_PATH");
-	if ( ldlp != 0 ) {
-		size_t len_atbd = strlen(ABS_TOP_BUILDDIR);
+	struct stat self;
+	if ( stat( "/proc/self/exe", &self ) == 0 )
+	{
+		struct stat colm;
+
+		if ( stat ( ABS_BUILDDIR "/" LT_OBJDIR "colm", &colm ) == 0 &&
+				self.st_dev == colm.st_dev && self.st_ino == colm.st_ino )
+		{
+			buildDir = ABS_TOP_BUILDDIR;
+			return;
+		}
 
-		if ( strlen(ldlp) > len_atbd &&
-				memcmp( ldlp, ABS_TOP_BUILDDIR "/", len_atbd+1) == 0 )
+		if ( stat ( ABS_BUILDDIR "/colm", &colm ) == 0 &&
+				self.st_dev == colm.st_dev && self.st_ino == colm.st_ino )
 		{
 			buildDir = ABS_TOP_BUILDDIR;
+			return;
 		}
 	}
 }