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 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?

Wei.

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