Merge lp:~gz/bzr/avoid_diff_delta_empty_malloc_856731 into lp:bzr/2.4

[Martin Packman]

Bug #856731, avoid calling malloc(0) for platforms that return NULL (such as AIX)

Very simple fix from John to avoid quirks with doing malloc(0) on some platforms.

I tested faking out that call point to behave in the funky manner reported, and running `bzr selftest -s bt.test_groupcompress` starts failing pretty hard, so there's clearly coverage for this problem on platforms where it can occur.

The bug was reported against 2.2 but I think 2.4 is far enough to go back, even with a change this minimal.

[John A Meinel (jameinel)]

I'm fine with this change, but it would be nice to actually run it on AIX to make sure it works as expected.

We should also audit to see if there are any other malloc(0) cases.

review: Approve

[Martin Packman (gz)]

> I'm fine with this change, but it would be nice to actually run it on AIX to
> make sure it works as expected.

I agree. I'll ask the bug reporter.

> We should also audit to see if there are any other malloc(0) cases.

Forgot to mention in the description, I went through diff-delta.c and this was the only possible one (it's not the only point to multiply by some value without also adding a sizeof(something) but it's the only one where malloc(0) can actually result).

[John A Meinel (jameinel)]

sent to pqm by email

[Martin Pool (mbp)]

Could be worth getting it checked by John too, but

  review approve

review: Approve

[John A Meinel (jameinel)]

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On 10/5/2011 3:25 AM, Martin Pool wrote:
> Review: Approve
>
> Could be worth getting it checked by John too, but
>
> review approve
>

Yeah, I was happy with it, and submitted it.

John
=:->
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=== modified file 'bzrlib/diff-delta.c'
--- bzrlib/diff-delta.c	2011-05-16 14:26:54 +0000
+++ bzrlib/diff-delta.c	2011-09-30 16:46:02 +0000
@@ -720,6 +720,11 @@
 
     max_num_entries = (src->size - 1)  / RABIN_WINDOW;
 
+    if (!max_num_entries) {
+        *fresh = old_index;
+        return DELTA_OK;
+    }
+
     /* allocate an array to hold whatever entries we find */
     entries = malloc(sizeof(*entry) * max_num_entries);
     if (!entries) /* malloc failure */

=== modified file 'doc/en/release-notes/bzr-2.4.txt'
--- doc/en/release-notes/bzr-2.4.txt	2011-09-29 14:58:56 +0000
+++ doc/en/release-notes/bzr-2.4.txt	2011-09-30 16:46:02 +0000
@@ -39,6 +39,10 @@
   stat fields into four bytes in dirstate pack_stat implementations.
   (Martin Packman, #683191 #706957)
 
+* Return early from create_delta_index_from_delta given tiny inputs. This
+  avoids raising a spurious MemoryError on certain platforms such as AIX.
+  (John Arbash Meinel, #856731)
+
 Documentation
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