[PATCH 3/6] sysroot: debuginfo lookup with sysroot case do not remove sysroot from file_name

[Victor Kamensky <kamensky at cisco dot com>]

If sysroot option is passed, and debug symbols reside in sysroot along
with executable <foo> in <foo_dir>/.debug/<foo_file> directory, stap
fails to find debuginfo because it strips out sysroot path from file_name
so dwfl_standard_find_debuginfo ends up looking at host
<foo_dir>/.debug/<foo_file> rather then checking
<sysroot>/<foo_dir>/.debug/<foo_file>.

Note in cross compile environment, it is good idea to set and export
proper SYSTEMTAP_DEBUGINFO_PATH variable because usual built defaults that
work for native distros very often not applicable to cross sysroot
based environment. For example for yocto poky/OE build the following
setting seems proper "+:.debug:build".

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

[kamensky@coreos-lnx2 tests]$ ls /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
/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 /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
/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]$ /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 -l 'process("/bin/mkdir.coreutils").function("*")'
Pass 1: parsed user script and 480 library scripts using 230184virt/93416res/5344shr/88612data kb, in 350usr/30sys/378real ms.
process("/bin/mkdir.coreutils").function("_fini")
process("/bin/mkdir.coreutils").function("_init")
process("/bin/mkdir.coreutils").function("fts_children")
process("/bin/mkdir.coreutils").function("fts_close")
process("/bin/mkdir.coreutils").function("fts_open")
process("/bin/mkdir.coreutils").function("fts_read")
process("/bin/mkdir.coreutils").function("fts_set")
Pass 2: analyzed script: 7 probes, 0 functions, 0 embeds, 0 globals using 233484virt/97928res/6212shr/91912data kb, in 20usr/0sys/26real ms.

running above example under strace shows that stap tries to access
/bin/.debug/mkdir.coreutils on host, rather then sysroot

13064 openat(AT_FDCWD, "/bin/mkdir.coreutils", O_RDONLY) = -1 ENOENT (No such file or directory)
13064 openat(AT_FDCWD, "/bin/.debug/mkdir.coreutils", O_RDONLY) = -1 ENOENT (No such file or directory)
13064 openat(AT_FDCWD, "/bin/mkdir.coreutils", O_RDONLY) = -1 ENOENT (No such file or directory)
13064 openat(AT_FDCWD, "/bin/build/mkdir.coreutils", O_RDONLY) = -1 ENOENT (No such file or directory)
13064 openat(AT_FDCWD, "/bin/mkdir.coreutils", O_RDONLY) = -1 ENOENT (No such file or directory)

After fix applied stap is able to find /bin/.debug/mkdir.coreutils under
sysroot:

[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 -l 'process("/bin/mkdir.coreutils").function("*")' | wc
Pass 1: parsed user script and 480 library scripts using 230184virt/93440res/5368shr/88612data kb, in 330usr/40sys/371real ms.
Pass 2: analyzed script: 401 probes, 0 functions, 0 embeds, 0 globals using 235092virt/99484res/6256shr/93520data kb, in 30usr/0sys/35real ms.
    249     249   29671

Also verified on target that script like example below, once compiled
against sysroot on host and copied back on target can trace 'mkdir'
invocation functions:

[kamensky@coreos-lnx2 tests]$ cat mkdir1.stp
probe process("/bin/mkdir.coreutils").function("*").call {
  printf ("%s -> %s\n", thread_indent(1), ppfunc())
}
probe process("/bin/mkdir.coreutils").function("*").return {
  printf ("%s <- %s\n", thread_indent(-1), ppfunc())
}

Signed-off-by: Victor Kamensky <kamensky@cisco.com>
---
 setupdwfl.cxx | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/setupdwfl.cxx b/setupdwfl.cxx
index f00cf755b..e5bfa28f0 100644
--- a/setupdwfl.cxx
+++ b/setupdwfl.cxx
@@ -637,18 +637,6 @@ internal_find_debuginfo (Dwfl_Module *mod,
 
   call_dwfl_standard_find_debuginfo:
 
-  if (current_session_for_find_debuginfo)
-    {
-      string sysroot = current_session_for_find_debuginfo->sysroot + "/*";
-      int    found   = fnmatch(sysroot.c_str(), file_name, 0);
-
-      if (found)
-	{
-	  file_name = file_name
-	    + current_session_for_find_debuginfo->sysroot.length() - 1;
-	}
-    }
-
   /* Call the original dwfl_standard_find_debuginfo */
   return dwfl_standard_find_debuginfo(mod, userdata, modname, base,
               file_name, debuglink_file,
-- 
2.14.3