Re: [PATCH] add-symbol-file-from-memory command

[Roland McGrath <roland@redhat.com>]

> I can't approve this patch, but I have some comments anyway.

Much appreciated.

> There also was a segfault when the objfile is released.  To reproduce,
> I could just say "file\n" after loading one.  GDB will try to
> xfree("<in-memory>").  I see that this is fixed in the patch below, so
> if the bits were unchanged from your last post then I must have come up
> with the wrong copy.

I won't testify to not having noticed and fixed (and since forgotten) some
small bug like this between the last time I posted and today.  Probably I did.

> I can tell you one problem with this patch, based on my backport of it:
> there's an annoying/incorrect message when a program is re-run, saying:
>    "<in-memory>" has disappeared; keeping its symbols
> 
> This is merely an annoyance, the message is harmless but should be
> fixed.

I don't see this.  AFAICT it just loses the symbols, like it should.  What
exactly is the recipe for seeing this?  This may be something else I forgot
I changed.  It sets the OBJF_SHARED flag, which means the objfile is
dropped by objfile_purge_solibs for "run".

> Mind doing this in some way that isn't gratuitously quadratic?

Sure.  I only used bfd_map_over_sections since it was said to be preferred.

> Please remove the check and the !from_tty branch.  An error is fine in
> either case, and internal errors are not appropriate for user input.
> Further down you have different error behavior on !from_tty also.  Is
> there a particular inspiration for this?

My thinking was that when there are later internal calls to this function
from target code, it would be an indication of a bug in the target code if
it ever got called for a non-ELF target, and those would be the called with
from_tty==0, hence the gdb_assert.  The other errors indicate that the
thing was reasonable to attempt, but failed.  I think I copied the from_tty
conditional for those errors from some other code I found similar, but I
may be misremembering.  I am more than happy to have you tell me a clear
policy on what from_tty should or shouldn't affect.

> > +  reinit_frame_cache ();	/* ??? */
> 
> Yes, this is necessary if the current cached backtrace would pass
> through the newly loaded object.

I appreciate the explanation.  I've added a comment.  
I'm appending my current version of the symfile.c part of the patch.


Thanks,
Roland

Index: symfile.c
===================================================================
RCS file: /cvs/src/src/gdb/symfile.c,v
retrieving revision 1.117
diff -u -b -p -r1.117 symfile.c
--- symfile.c	23 Jan 2004 17:56:46 -0000	1.117
+++ symfile.c	2 Feb 2004 04:41:50 -0000
@@ -799,6 +799,10 @@ new_symfile_objfile (struct objfile *obj
    NAME is the file name (which will be tilde-expanded and made
    absolute herein) (but we don't free or modify NAME itself).
 
+   If ABFD is not null, it's already open and should be used instead of
+   opening the file by name.  This BFD will be closed on error, and
+   is always consumed by this function.
+
    FROM_TTY says how verbose to be.
 
    MAINLINE specifies whether this is the main symbol file, or whether
@@ -811,7 +815,7 @@ new_symfile_objfile (struct objfile *obj
    Upon success, returns a pointer to the objfile that was added.
    Upon failure, jumps back to command level (never returns). */
 static struct objfile *
-symbol_file_add_with_addrs_or_offsets (char *name, int from_tty,
+symbol_file_add_with_addrs_or_offsets (char *name, bfd *abfd, int from_tty,
                                        struct section_addr_info *addrs,
                                        struct section_offsets *offsets,
                                        int num_offsets,
@@ -820,15 +824,17 @@ symbol_file_add_with_addrs_or_offsets (c
   struct objfile *objfile;
   struct partial_symtab *psymtab;
   char *debugfile;
-  bfd *abfd;
   struct section_addr_info *orig_addrs;
   struct cleanup *my_cleanups;
 
   /* Open a bfd for the file, and give user a chance to burp if we'd be
      interactively wiping out any existing symbols.  */
 
+  if (abfd == NULL)
   abfd = symfile_bfd_open (name);
 
+  my_cleanups = make_cleanup_bfd_close (abfd);
+
   if ((have_full_symbols () || have_partial_symbols ())
       && mainline
       && from_tty
@@ -836,6 +842,7 @@ symbol_file_add_with_addrs_or_offsets (c
     error ("Not confirmed.");
 
   objfile = allocate_objfile (abfd, flags);
+  discard_cleanups (my_cleanups);
 
   orig_addrs = alloc_section_addr_info (bfd_count_sections (abfd));
   my_cleanups = make_cleanup (xfree, orig_addrs);
@@ -952,7 +959,8 @@ struct objfile *
 symbol_file_add (char *name, int from_tty, struct section_addr_info *addrs,
 		 int mainline, int flags)
 {
-  return symbol_file_add_with_addrs_or_offsets (name, from_tty, addrs, 0, 0, 
+  return symbol_file_add_with_addrs_or_offsets (name, NULL, from_tty,
+						addrs, 0, 0,
                                                 mainline, flags);
 }
 
@@ -1802,6 +1810,90 @@ add_shared_symbol_files_command (char *a
 #endif
 }
 \f
+/* Read inferior memory at ADDR to find the header of a loaded object file
+   and read its in-core symbols out of inferior memory.  TEMPL is a bfd
+   representing the target's format.  */
+struct objfile *
+symbol_file_add_from_memory (bfd *templ, CORE_ADDR addr, int from_tty)
+{
+  struct objfile *objf;
+  bfd *nbfd;
+  asection *sec;
+  bfd_vma loadbase;
+  struct section_addr_info *sai;
+  unsigned int i;
+
+  if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
+    error ("add-symbol-file-from-memory not supported for this target");
+
+  nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
+					 target_read_memory);
+  if (nbfd == NULL)
+    {
+      if (from_tty)
+	error ("Failed to read a valid object file image from memory.");
+      return NULL;
+    }
+
+  nbfd->filename = xstrdup ("shared object read from target memory");
+
+  if (!bfd_check_format (nbfd, bfd_object))
+    {
+      /* FIXME: should be checking for errors from bfd_close (for one thing,
+         on error it does not free all the storage associated with the
+         bfd).  */
+      bfd_close (nbfd);
+      if (from_tty)
+	error ("Got object file from memory but can't read symbols: %s.",
+	       bfd_errmsg (bfd_get_error ()));
+      return NULL;
+    }
+
+  sai = alloc_section_addr_info (bfd_count_sections (nbfd));
+  make_cleanup (xfree, sai);
+  i = 0;
+  for (sec = nbfd->sections; sec != NULL; sec = sec->next)
+    if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
+      {
+	sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
+	sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
+	sai->other[i].sectindex = sec->index;
+	++i;
+      }
+
+  objf = symbol_file_add_with_addrs_or_offsets ((char *) nbfd->filename, nbfd,
+						from_tty, sai, NULL, 0, 0,
+						OBJF_SHARED);
+
+  /* This might change our ideas about frames already looked at.  */
+  reinit_frame_cache ();
+
+  return objf;
+}
+
+static void
+add_symbol_file_from_memory_command (char *args, int from_tty)
+{
+  CORE_ADDR addr;
+  bfd *templ;
+
+  if (args == NULL)
+    error ("add-symbol-file-from-memory requires an expression argument");
+
+  addr = parse_and_eval_address (args);
+
+  /* We need some representative bfd to know the target we are looking at.  */
+  if (symfile_objfile != NULL)
+    templ = symfile_objfile->obfd;
+  else
+    templ = exec_bfd;
+  if (templ == NULL)
+    error ("\
+Must use symbol-file or exec-file before add-symbol-file-from-memory.");
+
+  (void) symbol_file_add_from_memory (templ, addr, from_tty);
+}
+\f
 /* Re-read symbols if a symbol-file has changed.  */
 void
 reread_symbols (void)
@@ -2063,7 +2155,7 @@ reread_separate_symbols (struct objfile 
          Preserve the flags from objfile that make sense.  */
       objfile->separate_debug_objfile
         = (symbol_file_add_with_addrs_or_offsets
-           (debug_file,
+           (debug_file, NULL,
             info_verbose, /* from_tty: Don't override the default. */
             0, /* No addr table.  */
             objfile->section_offsets, objfile->num_sections,
@@ -3566,6 +3658,13 @@ with the text.  SECT is a section name t
 	       &cmdlist);
   set_cmd_completer (c, filename_completer);
 
+  c = add_cmd ("add-symbol-file-from-memory", class_files,
+	       add_symbol_file_from_memory_command,
+	       "Usage: add-symbol-file-from-memory ADDR\n\
+Load the symbols out of memory from a dynamically loaded object file.\n\
+ADDR is the starting address of the file's shared object file header.",
+	       &cmdlist);
+
   c = add_cmd ("add-shared-symbol-files", class_files,
 	       add_shared_symbol_files_command,
    "Load the symbols from shared objects in the dynamic linker's link map.",