libdwfl: Make dwfl_linux_proc_attach work even without any Dwfl_Modules.

dwfl_linux_proc_attach depended on a Dwfl_Module with the correct
ELF header already being available. That isn't really necessary since
when we attach we have the main exe ELF file available. Just use that
to make dwfl_linux_proc_attach always work.

Signed-off-by: Mark Wielaard <[email protected]>

3 files changed, 48 insertions, 6 deletions

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 2c763698..0e3b7862 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,9 @@
+2015-09-08  Mark Wielaard  <[email protected]>
+
+	* libdwflP.h (struct __libdwfl_pid_arg): Add elf and elf_fd.
+	* linux-pid-attach.c (pid_detach): Call elf_end and close.
+	(dwfl_linux_proc_attach): Open and save /proc/PID/exe.
+
 2015-09-04  Chih-Hung Hsieh  <[email protected]
 
 	* frame_unwind.c (expr_eval): Use llabs instead of abs.
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 12ee116e..42a2669e 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -400,7 +400,12 @@ struct dwfl_arange
    then get the instance through __libdwfl_get_pid_arg.  */
 struct __libdwfl_pid_arg
 {
+  /* /proc/PID/task/.  */
   DIR *dir;
+  /* Elf for /proc/PID/exe.  Set to NULL if it couldn't be opened.  */
+  Elf *elf;
+  /* fd for /proc/PID/exe.  Set to -1 if it couldn't be opened.  */
+  int elf_fd;
   /* It is 0 if not used.  */
   pid_t tid_attached;
   /* Valid only if TID_ATTACHED is not zero.  */
diff --git a/libdwfl/linux-pid-attach.c b/libdwfl/linux-pid-attach.c
index ae717028..4c0f42d8 100644
--- a/libdwfl/linux-pid-attach.c
+++ b/libdwfl/linux-pid-attach.c
@@ -1,5 +1,5 @@
 /* Get Dwarf Frame state for target live PID process.
-   Copyright (C) 2013, 2014 Red Hat, Inc.
+   Copyright (C) 2013, 2014, 2015 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -26,7 +26,11 @@
    the GNU Lesser General Public License along with this program.  If
    not, see <http://www.gnu.org/licenses/>.  */
 
+#include "libelfP.h"
 #include "libdwflP.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include <sys/ptrace.h>
 #include <sys/wait.h>
 #include <dirent.h>
@@ -247,6 +251,8 @@ static void
 pid_detach (Dwfl *dwfl __attribute__ ((unused)), void *dwfl_arg)
 {
   struct __libdwfl_pid_arg *pid_arg = dwfl_arg;
+  elf_end (pid_arg->elf);
+  close (pid_arg->elf_fd);
   closedir (pid_arg->dir);
   free (pid_arg);
 }
@@ -332,28 +338,53 @@ dwfl_linux_proc_attach (Dwfl *dwfl, pid_t pid, bool assume_ptrace_stopped)
       goto fail;
     }
 
-  char dirname[64];
-  int i = snprintf (dirname, sizeof (dirname), "/proc/%ld/task", (long) pid);
-  assert (i > 0 && i < (ssize_t) sizeof (dirname) - 1);
-  DIR *dir = opendir (dirname);
+  char name[64];
+  int i = snprintf (name, sizeof (name), "/proc/%ld/task", (long) pid);
+  assert (i > 0 && i < (ssize_t) sizeof (name) - 1);
+  DIR *dir = opendir (name);
   if (dir == NULL)
     {
       err = errno;
       goto fail;
     }
+
+  Elf *elf;
+  i = snprintf (name, sizeof (name), "/proc/%ld/exe", (long) pid);
+  assert (i > 0 && i < (ssize_t) sizeof (name) - 1);
+  int elf_fd = open (name, O_RDONLY);
+  if (elf_fd >= 0)
+    {
+      elf = elf_begin (elf_fd, ELF_C_READ_MMAP, NULL);
+      if (elf == NULL)
+	{
+	  /* Just ignore, dwfl_attach_state will fall back to trying
+	     to associate the Dwfl with one of the existing DWfl_Module
+	     ELF images (to know the machine/class backend to use).  */
+	  close (elf_fd);
+	  elf_fd = -1;
+	}
+    }
+  else
+    elf = NULL;
   struct __libdwfl_pid_arg *pid_arg = malloc (sizeof *pid_arg);
   if (pid_arg == NULL)
     {
+      elf_end (elf);
+      close (elf_fd);
       closedir (dir);
       err = ENOMEM;
       goto fail;
     }
   pid_arg->dir = dir;
+  pid_arg->elf = elf;
+  pid_arg->elf_fd = elf_fd;
   pid_arg->tid_attached = 0;
   pid_arg->assume_ptrace_stopped = assume_ptrace_stopped;
-  if (! INTUSE(dwfl_attach_state) (dwfl, NULL, pid, &pid_thread_callbacks,
+  if (! INTUSE(dwfl_attach_state) (dwfl, elf, pid, &pid_thread_callbacks,
 				   pid_arg))
     {
+      elf_end (elf);
+      close (elf_fd);
       closedir (dir);
       free (pid_arg);
       return -1;