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Re: [patch] Set bfd field in target_section

Pedro Alves wrote:
On Tuesday 28 July 2009 16:16:23, Aleksandar Ristovski wrote:
Pedro Alves wrote:
I think now you broke it in a different way. Now we can end up trying to read from a closed bfd.

Ooops, you're right. There are uses of the bfd after transfering its ownership to the bfd target with target_bfd_reopen, and closing the bfd target (target_close)... This target is modeled on fdopen, which is why I blindly assumed it wasn't happening. I've reverted that patch.

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);

Still not right, because that's still papering over the problem, and still hitting undefined behaviour, in the case of the table ending up being empty. When table->sections == table->sections_end, we should never dereference table->sections, like in 'table->sections->bfd'. Notice how the end pointer isn't advanced if !SEC_ALLOC. Consider the fact that we usually xmalloc enough memory that makes that not misbehave a coincidence. E.g., see that with a resize_section_table call, you can end up with table->sections == NULL, and table->section_end == NULL, which is legal, because table->sections is still equal to table->sections_end in that case (meaning empty table).

There used to be an extra structure in bfd_target.c to hold
the sections and the bfd, which didn't look necessary when I
reimplemented bfd-target.c on top of exec.c's functions, but
it is clear now that we need it anyway.  Here's a patch that
brings something like that back.

Could you try it? Thanks.

I tried it, it works.

Thanks, -- Aleksandar Ristovski QNX Software Systems

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