Re: [Xen-devel] [PATCH v2] tools/xenstore: try to get minimum thread stack size for watch thread

[Juergen Gross <jgross@xxxxxxxx>]

On 02/03/18 13:40, Wei Liu wrote:
> On Fri, Mar 02, 2018 at 12:29:31PM +0000, Wei Liu wrote:
>> On Mon, Feb 26, 2018 at 09:53:38AM -0700, Jim Fehlig wrote:
>>> On 02/26/2018 01:46 AM, Juergen Gross wrote:
>>>> When creating a pthread in xs_watch() try to get the minimal needed
>>>> size of the thread from glibc instead of using a constant. This avoids
>>>> problems when the library is used in programs with large per-thread
>>>> memory.
>>>>
>>>> Use dlsym() to get the pointer to __pthread_get_minstack() in order to
>>>> avoid linkage problems and fall back to the current constant size if
>>>> not found.
>>>>
>>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>>> ---
>>>> V2:
>>>> - use _GNU_SOURCE (Wei Liu)
>>>> - call __pthread_get_minstack() with parameter
>>>> - add -ldl to correct make flags
>>>> - ensure to not using smaller stack size than today
>>>> ---
>>>>   tools/xenstore/Makefile |  4 ++++
>>>>   tools/xenstore/xs.c     | 21 ++++++++++++++++++++-
>>>>   2 files changed, 24 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/tools/xenstore/Makefile b/tools/xenstore/Makefile
>>>> index 2b99d2bc1b..0831be0b6f 100644
>>>> --- a/tools/xenstore/Makefile
>>>> +++ b/tools/xenstore/Makefile
>>>> @@ -100,6 +100,10 @@ libxenstore.so.$(MAJOR): 
>>>> libxenstore.so.$(MAJOR).$(MINOR)
>>>>    ln -sf $< $@
>>>>   xs.opic: CFLAGS += -DUSE_PTHREAD
>>>> +ifeq ($(CONFIG_Linux),y)
>>>> +xs.opic: CFLAGS += -DUSE_DLSYM
>>>> +libxenstore.so.$(MAJOR).$(MINOR): LDFLAGS += -ldl
>>>> +endif
>>>
>>> Dropping this patch in one of my automated builds caused a libxenstore link 
>>> failure
>>>
>>> [   99s] gcc    -lsystemd -ldl -pthread -Wl,-soname -Wl,libxenstore.so.3.0
>>> -shared -o libxenstore.so.3.0.3 xs.opic xs_lib.opic 
>>> /home/abuild/rpmbuild/BUILD/xen-4.10.0-testing/tools/xenstore/../../tools/libs/toolcore/libxentoolcore.so
>>>
>>> [   99s] 
>>> /home/abuild/rpmbuild/BUILD/xen-4.10.0-testing/tools/xenstore/../../tools/xenstore/libxenstore.so:
>>> undefined reference to `dlsym'
>>>
>>> I hacked around it by appending '-ldl' to the end of the subsequent
>>> libxenstore.so rule.
>>
>> Hmm... Maybe I'm a bit dense today. I know the position of -l matters
>> but I don't quite understand how placing -pthread before xs.opic works
>> but -ldl doesn't. xs.c uses both after all.
> 
> I'm indeed very dense -- -pthread is a special option that sets the
> proper flags for linking pthread library for both the preprocessor and
> linker.
> 
> But still, Juergen must have tested the change, so I wonder why it
> doesn't work in your setup. What is your build environment? Gcc version?

And why is "-lsystemd" working correctly?

I have tested with gcc 4.8.5, binutils 2.25.0


Juergen


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