[jira] [Commented] (THRIFT-1248) pointer subtraction in TMemoryBuffer relies on undefined behavior

["Jens Geyer (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-1248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13679012#comment-13679012 ] 

Jens Geyer commented on THRIFT-1248:
------------------------------------

[~fanatoly], 
I see the point. Could you please
 * rebase the patch to current trunk
 * have a look whether wBound_ is really calculated correctly after your modifications being applied?

Thank you!

                
> pointer subtraction in TMemoryBuffer relies on undefined behavior
> -----------------------------------------------------------------
>
>                 Key: THRIFT-1248
>                 URL: https://issues.apache.org/jira/browse/THRIFT-1248
>             Project: Thrift
>          Issue Type: Bug
>          Components: C++ - Library
>    Affects Versions: 0.5
>            Reporter: Anatoly Fayngelerin
>            Assignee: Anatoly Fayngelerin
>             Fix For: 1.0
>
>         Attachments: 0_7_0_ptrdiff.patch
>
>
> The ensureCanWrite function in TMemoryBuffer currently "rebases" the buffer pointers by subtracting the original buffer pointer from the pointer newly returned by realloc. While this seems to work fine on my linux setup(I couldn't force a reproducer), pointer subtraction between pointers that we allocated separately is an undefined operation.
> I have run into problems with this on platforms other than linux.
> I am attaching a patch that removes the undefined operation.

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