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[RFC] elfutils: Checks for debuginfo file without .debug extension as well


Elfutils, looking for kernel debuginfo file, tries to find it at
various places. If elfutils finds /boot/vmlinu*x* file, it checks
for debufginfo section. If debuginfo is not present, it saves it as
'main elf' and continue looking for debuginfo file having .debug
extension i.e. vmlinux-RELEASE.debug.

'Ubuntu on powerpc' installs kernel as /boot/vmlinux and installs
debuginfo without any extension as /usr/lib/debug/boot/vmlinux-RELEASE
and hence, elfutils is not able to find the debuginfo file.

Here is the lunchpad bug for the same:
  https://bugs.launchpad.net/ubuntu/+source/systemtap/+bug/1537125

This patch adds functionality to search for file without any extension
followed by searching file having .debug extension.

I've formatted this patch from elfutils-0.165

Before applying patch:

  # strace -o out -e open ./stap -v probe.stp
  Pass 1: parsed user script and 95 library script(s) using 42176virt/32128res/5952shr/25472data kb, in 190usr/20sys/222real ms.
  WARNING: cannot find module kernel debuginfo: No DWARF information found [man warning::debuginfo]
  semantic error: while resolving probe point: identifier 'kernel' at probe.stp:1:7
          source: probe kernel.function("do_fork")
                      ^

  semantic error: no match
  Pass 2: analyzed script: 0 probe(s), 0 function(s), 0 embed(s), 0 global(s) using 66688virt/34496res/7296shr/26432data kb, in 0usr/0sys/28real ms.
  Pass 2: analysis failed.  [man error::pass2]
  Tip: /usr/share/doc/systemtap/README.Debian should help you get started.

  # cat out | grep vmlinu
  open("/boot/vmlinux-3.13.0-76-generic", O_RDONLY) = 3
  open("/lib/modules/3.13.0-76-generic/build/vmlinux.id", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/.debug/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/usr/lib/debug/boot/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/var/cache/abrt-di/usr/lib/debug/boot/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/build/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/.debug/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/usr/lib/debug/boot/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/var/cache/abrt-di/usr/lib/debug/boot/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/build/vmlinux-3.13.0-76-generic.debug", O_RDONLY) = -1 ENOENT (No such file or directory)

After applying patch:

  # strace -o out1 -e open ./stap -v probe.stp
  Pass 1: parsed user script and 95 library script(s) using 41856virt/32128res/5952shr/25472data kb, in 170usr/10sys/189real ms.
  Pass 2: analyzed script: 1 probe(s), 0 function(s), 0 embed(s), 0 global(s) using 242496virt/166912res/105088shr/60608data kb, in 700usr/100sys/1518real ms.
  Pass 3: translated to C into "/tmp/stapbbBu6y/stap_a18833407fc7a78b1251d743383f3fef_989_src.c" using 242496virt/167040res/105216shr/60608data kb, in 0usr/0sys/9real ms.
  Pass 4: compiled C into "stap_a18833407fc7a78b1251d743383f3fef_989.ko" in 6710usr/820sys/8338real ms.
  Pass 5: starting run.
  ^CPass 5: run completed in 0usr/10sys/3477real ms.

  # cat out1 | grep vmlinu
  open("/boot/vmlinux-3.13.0-76-generic", O_RDONLY) = 3
  open("/lib/modules/3.13.0-76-generic/build/vmlinux.id", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/vmlinux-3.13.0-76-generic", O_RDONLY) = 4
  open("/boot/.debug/vmlinux-3.13.0-76-generic", O_RDONLY) = -1 ENOENT (No such file or directory)
  open("/boot/vmlinux-3.13.0-76-generic", O_RDONLY) = 4
  open("/usr/lib/debug/boot/vmlinux-3.13.0-76-generic", O_RDONLY) = 4

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
---
 libdwfl/dwfl_module_getdwarf.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/libdwfl/dwfl_module_getdwarf.c b/libdwfl/dwfl_module_getdwarf.c
index 0e8810b..ad5054b 100644
--- a/libdwfl/dwfl_module_getdwarf.c
+++ b/libdwfl/dwfl_module_getdwarf.c
@@ -529,11 +529,22 @@ find_debuginfo (Dwfl_Module *mod)
   debuglink_file = INTUSE(dwelf_elf_gnu_debuglink) (mod->main.elf,
 						    &debuglink_crc);
 
-  mod->debug.fd = (*mod->dwfl->callbacks->find_debuginfo) (MODCB_ARGS (mod),
-							   mod->main.name,
-							   debuglink_file,
-							   debuglink_crc,
-							   &mod->debug.name);
+  /* First try to look for vmlinux file */
+  if (debuglink_file == NULL)
+    mod->debug.fd = (*mod->dwfl->callbacks->find_debuginfo) (MODCB_ARGS (mod),
+							     mod->main.name,
+							     basename(mod->main.name),
+							     debuglink_crc,
+							     &mod->debug.name);
+
+  /* Try to look for vmlinux.debug file */
+  if (mod->debug.fd <= 0)
+    mod->debug.fd = (*mod->dwfl->callbacks->find_debuginfo) (MODCB_ARGS (mod),
+							     mod->main.name,
+							     debuglink_file,
+							     debuglink_crc,
+							     &mod->debug.name);
+
   Dwfl_Error result = open_elf (mod, &mod->debug);
   if (result == DWFL_E_NOERROR && mod->debug.address_sync != 0)
     result = find_prelink_address_sync (mod, &mod->debug);
-- 
1.9.1

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