bbuesker at qualcomm
Jun 29, 2008, 9:44 AM
Post #2 of 2
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Re: apr_bucket_type_{eos,file,flush} being defined in BSS of httpd during build
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Brian Buesker wrote:
> I was debugging some issues related to locking in mod_dav_svn this week,
> and eventually tracked down the problem to the fact that
> apr_bucket_type_eos was being included in the BSS segment of the httpd
> executable (two other apr_bucket_types are also included in the BSS).
> This definition causes usage of APR_BUCKET_IS_EOS to fail in mod_dav_svn.
>
> From what I can tell, these symbols should not be defined in the httpd
> executable but instead should be picked up from the apr-util library. nm
> shows these symbols in the Data segment of libapr-util-1.so.0.2.12, but
> also in the BSS of httpd of my vanilla httpd build. The RHEL5U2 build
> only shows them in the data segment of the apr-util library.
>
> # nm .libs/httpd | grep apr_bucket_type
> 0000000000688880 B apr_bucket_type_eos
> 0000000000688840 B apr_bucket_type_file
> 00000000006888c0 B apr_bucket_type_flush
>
> # nm srclib/apr-util/.libs/libaprutil-1.so.0.2.12 | grep apr_bucket_type
> 0000000000218180 D apr_bucket_type_eos
> 00000000002181c0 D apr_bucket_type_file
> 0000000000218200 D apr_bucket_type_flush
> 0000000000218240 D apr_bucket_type_heap
> 0000000000218340 D apr_bucket_type_immortal
> 0000000000218280 D apr_bucket_type_mmap
> 00000000002182c0 D apr_bucket_type_pipe
> 0000000000218300 D apr_bucket_type_pool
> 00000000002183c0 D apr_bucket_type_socket
> 0000000000218380 D apr_bucket_type_transient
>
> # nm /usr/lib/debug/usr/sbin/httpd.debug | grep apr_bucket_type
> U apr_bucket_type_eos
> U apr_bucket_type_file
> U apr_bucket_type_flush
>
> I tried doing an nm on all the .o's and .a's in a build to see if any of
> them happened to have these symbols in the BSS, but sure enough, they
> did not.
>
> Does anyone have an idea of what could be causing these symbols to be
> included in httpd's uninitialized data (BSS) segment? Are there any
> suggested workarounds? The only workaround (which is more of a hack than
> anything else) I've come up with right now is to modify
> APR_BUCKET_IS_EOS to do a strcmp on the type name rather than comparing
> the pointer values.
>
In case anybody else runs into this, I eventually found that by building apache with --enable-pie, these symbols were not included in the BSS, and locking with mod_dav_svn worked just fine.
Brian
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