[PATCH 5/6] sysroot: handle symbolic links with absolute name relative to sysroot

[Victor Kamensky <kamensky at cisco dot com>]

In case of symbolic link found under sysroot point to absolute path,
instead of trying to look for such absolute path in host system,
apply sysroot prefix first.

Here are steps how to reproduce the issue. Note <sysroot> is produced by
yocto poky build.

kamensky@coreos-lnx2 tests]$ ls -l /home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs/bin/mkdir
lrwxrwxrwx. 1 kamensky kamensky 20 Jan 30 18:29 /home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs/bin/mkdir -> /bin/mkdir.coreutils
[kamensky@coreos-lnx2 tests]$ ls -l /home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs/bin/mkdir.coreutils
-rwxr-xr-x. 1 kamensky kamensky 88232 Jan 29 09:58 /home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs/bin/mkdir.coreutils
[kamensky@coreos-lnx2 tests]$ ls -l /home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs/bin/.debug/mkdir.coreutils
-rwxr-xr-x. 1 kamensky kamensky 383456 Jan 29 09:58 /home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs/bin/.debug/mkdir.coreutils
[kamensky@coreos-lnx2 tests]$ cat mkdir4.stp
probe process("/bin/mkdir").function("*").call {
  printf ("%s -> %s\n", thread_indent(1), ppfunc())
}
probe process("/bin/mkdir").function("*").return {
  printf ("%s <- %s\n", thread_indent(-1), ppfunc())
}
[kamensky@coreos-lnx2 tests]$ /home/wd8/systemtap/20180208_2/packages/bin/stap --sysroot=/home/wd8/yocto/20180128/build_x86_64/tmp/work/intel_corei7_64-poky-linux/kdevel-console-devel-image/1.0-r0/rootfs -a x86_64 -r 4.9.78-yocto-standard -B CROSS_COMPILE=x86_64-poky-linux- --sysenv=PATH=/usr/bin:/bin:/usr/sbin:/sbin --sysenv=LD_LIBRARY_PATH=/lib:/usr/lib -v -p4 -m mkdir4 mkdir4.stp
Pass 1: parsed user script and 480 library scripts using 230196virt/93484res/5396shr/88624data kb, in 340usr/30sys/370real ms.
semantic error: resolution failed in DWARF builder

semantic error: while resolving probe point: identifier 'process' at mkdir4.stp:1:7
        source: probe process("/bin/mkdir").function("*").call {
                      ^

semantic error: no match

semantic error: resolution failed in DWARF builder

semantic error: while resolving probe point: identifier 'process' at :4:7
        source: probe process("/bin/mkdir").function("*").return {
                      ^

semantic error: no match

Pass 2: analyzed script: 0 probes, 0 functions, 0 embeds, 0 globals using 233496virt/96980res/5468shr/91924data kb, in 20usr/0sys/25real ms.
Pass 2: analysis failed.  [man error::pass2]

After the fix above sript works fine verified that it traces mkdir
functions on target.

Signed-off-by: Victor Kamensky <kamensky@cisco.com>
---
 util.cxx | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/util.cxx b/util.cxx
index 2724be956..f48a8884f 100644
--- a/util.cxx
+++ b/util.cxx
@@ -443,6 +443,64 @@ split_lines(const char *buf, size_t n)
   return lines;
 }
 
+static string
+follow_link(const string& name, const string& sysroot)
+{
+  char *linkname;
+  ssize_t r;
+  string retpath;
+  struct stat st;
+
+  const char *f = name.c_str();
+
+  lstat(f, &st);
+
+  linkname = (char *) malloc(st.st_size + 1);
+
+  if (linkname)
+    {
+      r = readlink(f, linkname, st.st_size + 1);
+      linkname[st.st_size] = '\0';
+      /*
+       * If we have non-empty sysroot and we got link that
+       * points to absolute path name, we need to look at
+       * this path relative to sysroot itself. access and
+       * stat will follow symbolic links correctly only in
+       * case with empty sysroot.
+       */
+      while (r != -1 && linkname && linkname[0] == '/')
+	{
+	  string fname1 = sysroot + linkname;
+	  const char *f1 = fname1.c_str();
+	  if (access(f1, X_OK) == 0
+	      && stat(f1, &st) == 0
+	      && S_ISREG(st.st_mode))
+	    {
+	      retpath = fname1;
+	      break;
+	    }
+	  else if (lstat(f1, &st) == 0
+		   && S_ISLNK(st.st_mode))
+	    {
+	      free(linkname);
+	      linkname = (char *) malloc(st.st_size + 1);
+	      if (linkname)
+		{
+		  r = readlink(f1, linkname, st.st_size + 1);
+		  linkname[st.st_size] = '\0';
+		}
+	    }
+	  else
+	    {
+	      break;
+	    }
+	}
+    }
+  free(linkname);
+
+  return retpath;
+}
+
 // Resolve an executable name to a canonical full path name, with the
 // same policy as execvp().  A program name not containing a slash
 // will be searched along the $PATH.
@@ -467,6 +525,14 @@ string find_executable(const string& name, const string& sysroot,
   if (name.find('/') != string::npos) // slash in the path already?
     {
       retpath = sysroot + name;
+
+      const char *f = retpath.c_str();
+      if (sysroot != ""
+	  && lstat(f, &st) == 0
+	  && S_ISLNK(st.st_mode))
+	{
+	  retpath = follow_link(f, sysroot);
+	}
     }
   else // Nope, search $PATH.
     {
@@ -495,6 +561,16 @@ string find_executable(const string& name, const string& sysroot,
                   retpath = fname;
                   break;
                 }
+              else if (sysroot != ""
+                       && lstat(f, &st) == 0
+                       && S_ISLNK(st.st_mode))
+		{
+		  retpath = follow_link(f, sysroot);
+		  if (retpath != "")
+		    {
+		      break;
+		    }
+		}
             }
         }
     }
-- 
2.14.3