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

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

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>
- 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 $< $@
+ifeq ($(CONFIG_Linux),y)
+xs.opic: CFLAGS += -DUSE_DLSYM
+libxenstore.so.$(MAJOR).$(MINOR): LDFLAGS += -ldl

Dropping this patch in one of my automated builds caused a libxenstore link 

[ 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.

  libxenstore.so.$(MAJOR).$(MINOR): xs.opic xs_lib.opic
-Wl,libxenstore.so.$(MAJOR) $(SHLIB_LDFLAGS) -o $@ $^ $(LDLIBS_libxentoolcore) 
diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index abffd9cd80..77700bff2b 100644
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -16,6 +16,8 @@
      License along with this library; If not, see 
+#define _GNU_SOURCE
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
@@ -47,6 +49,10 @@ struct xs_stored_msg {
#include <pthread.h> +#ifdef USE_DLSYM
+#include <dlfcn.h>
  struct xs_handle {
        /* Communications channel to xenstore daemon. */
        int fd;
@@ -810,12 +816,25 @@ bool xs_watch(struct xs_handle *h, const char *path, 
const char *token)
        if (!h->read_thr_exists) {
                sigset_t set, old_set;
                pthread_attr_t attr;
+               static size_t stack_size;
+#ifdef USE_DLSYM
+               size_t (*getsz)(pthread_attr_t *attr);
if (pthread_attr_init(&attr) != 0) {
                        return false;
-               if (pthread_attr_setstacksize(&attr, READ_THREAD_STACKSIZE) != 
0) {
+               if (!stack_size) {
+#ifdef USE_DLSYM
+                       getsz = dlsym(RTLD_DEFAULT, "__pthread_get_minstack");
+                       if (getsz)
+                               stack_size = getsz(&attr);
+                       if (stack_size < READ_THREAD_STACKSIZE)
+                               stack_size = READ_THREAD_STACKSIZE;
+               }
+               if (pthread_attr_setstacksize(&attr, stack_size) != 0) {
                        return false;

This worked fine, even on the system with the buggy glibc.

Tested-by: Jim Fehlig <jfehlig@xxxxxxxx>


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