[RFC PATCH] nptl_db/db_info: fix the incorrect initial size for dtvp

[Junling Zheng]

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On 2015/7/20 21:33, Junling Zheng wrote:
> When debugging a program on ARMv7 with thread-local storage declared using
> "__thread", attempting to print a thread-local variable will result in the
> following message:
> 
> Cannot find thread-local storage for Thread <snip> (LWP <snip>), executable
> file /tmp/tls: capability not available
> 
> This can be traced back to uclibc libpthread/nptl_db/td_thr_tls_get_addr.c
> which gdb uses to look up the address of the TLS. The function returns
> TD_NOCAPAB due to a mismatch in size between the DTV pointer and the size
> recorded in the db description. The problem lies in libpthread/nptl_db/db_info.c
> which initializes the db with the sizeof the union dtv. Instead it should
> be the sizeof a pointer to union dtv.
> 
> Fixed the initial size for dtvp to sizeof a pointer, instead of sizeof
> the union.
> 
> Refer to:
> http://sourceware.org/ml/libc-alpha/2006-10/msg00088.html
> https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=416b630981788c1f08e746e19765aa0e5c2a1360
> 
> Signed-off-by: Junling Zheng <zhengjunling at huawei.com>
> ---
>  libpthread/nptl_db/db_info.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libpthread/nptl_db/db_info.c b/libpthread/nptl_db/db_info.c
> index a57a053..159a027 100644
> --- a/libpthread/nptl_db/db_info.c
> +++ b/libpthread/nptl_db/db_info.c
> @@ -60,7 +60,7 @@ extern bool __nptl_initial_report_events;
>     i.e. at the very end of the area covered by TLS_PRE_TCB_SIZE.  */
>  DESC (_thread_db_pthread_dtvp,
>        TLS_PRE_TCB_SIZE + offsetof (tcbhead_t, dtv)
> -      - (TLS_TCB_SIZE == 0 ? sizeof (tcbhead_t) : 0), union dtv)
> +      - (TLS_TCB_SIZE == 0 ? sizeof (tcbhead_t) : 0), union dtv *)
>  #endif
>  
>  
>