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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Mar 02, 2018 at 01:45:14PM +0100, Juergen Gross wrote:
> 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?

That's red-herring because libxenstore doesn't use systemd functions.
The only place systemd is used is in xenstored_core.c -- calling
sd_notify.

But we still need to figure out why -ldl works in your setup but not
Jim's.

Wei.

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