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Re: [patch] Set bfd field in target_section

Pedro Alves wrote:
On Tuesday 28 July 2009 15:45:25, Aleksandar Ristovski wrote:
Pedro Alves wrote:
On Tuesday 28 July 2009 15:28:33, Aleksandar Ristovski wrote:

I believe this is related to Pedro's patch from 03-Jun-09. I didn't see where we set target_section.bfd field - maybe I am overlooking something, but in bfd-target, in function target_bfd_xclose we will call bfd_close (table->sections->bfd); bfd_close doesn't like NULL argument.

Am I missing something, or is this (the patch) missing?
Doesn't add_to_section_table set the bfd in each new
target section?
Indeed it does. However, the problem is if we don't find any sections in a bfd, it will exit and will leave bfd field 0.

Right, but table->sections will be equal to table->sections_end, meaning the table is empty. Your fix isn't correct, since you should never write to *sections_end, which is one-past-the-end of the sections in the table. In the degenerate case of bfd_count_sections == 0 (not 0 ALLOC sections), xmalloc will still return something non-NULL, but, writing to this pointer invokes undefined behaviour.

I get this situation at the moment because I broke my xfer_partial, but I think it could happen in general?

Testing finished succesfully, so I've applied the patch with this ChangeLog entry. Let me know if something is still wrong.

2009-07-28 Pedro Alves <>

	* bfd-target.c (target_bfd_xclose): Only close the bfd if the
	section table is not empty.
	(target_bfd_reopen): If the section table ends up empty, close the
	bfd here.

I think now you broke it in a different way. Now we can end up trying to read from a closed bfd.

And just wondering, why not simply:

Index: gdb/exec.c
RCS file: /cvs/src/src/gdb/exec.c,v
retrieving revision 1.90
diff -u -p -r1.90 exec.c
--- gdb/exec.c 2 Jul 2009 17:21:06 -0000 1.90
+++ gdb/exec.c 28 Jul 2009 14:58:16 -0000
@@ -381,6 +381,7 @@ add_to_section_table (bfd *abfd, struct
struct target_section **table_pp = (struct target_section **) table_pp_char;
flagword aflag;

+ (*table_pp)->bfd = abfd;
/* Check the section flags, but do not discard zero-length sections, since
some symbols may still be attached to this section. For instance, we
encountered on sparc-solaris 2.10 a shared library with an empty .bss
@@ -390,7 +391,6 @@ add_to_section_table (bfd *abfd, struct
if (!(aflag & SEC_ALLOC))

- (*table_pp)->bfd = abfd;
(*table_pp)->the_bfd_section = asect;
(*table_pp)->addr = bfd_section_vma (abfd, asect);
(*table_pp)->endaddr = (*table_pp)->addr + bfd_section_size (abfd, asect);

Aleksandar Ristovski
QNX Software Systems

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