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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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.

Wei.

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