[PATCH] linux-user: Use public sigev_notify_thread_id member if available

[Michael Forney <mforney@mforney.org>]

_sigev_un._tid is an internal glibc field and is not available on
musl libc. The sigevent(7) man page and Linux UAPI headers both use
sigev_notify_thread_id as a public way to access this field.

musl libc supports this field since 1.2.2[0], and glibc plans to
add support as well[1][2].

If sigev_notify_thread_id is not available, fall back to _sigev_un._tid
as before.

[0] http://git.musl-libc.org/cgit/musl/commit/?id=7c71792e87691451f2a6b76348e83ad1889f1dcb
[1] https://www.openwall.com/lists/musl/2019/08/01/5
[2] https://sourceware.org/bugzilla/show_bug.cgi?id=27417

Signed-off-by: Michael Forney <mforney@mforney.org>
---
 configure            | 16 ++++++++++++++++
 linux-user/syscall.c |  6 +++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index 676239c697..fa39b0a727 100755
--- a/configure
+++ b/configure
@@ -4462,6 +4462,19 @@ if compile_prog "" "" ; then
     st_atim=yes
 fi
 
+##########################################
+# check if we have sigev_notify_thread_id
+
+sigev_notify_thread_id=no
+cat > $TMPC << EOF
+#include <stddef.h>
+#include <signal.h>
+int main(void) { return offsetof(struct sigevent, sigev_notify_thread_id); }
+EOF
+if compile_prog "" "" ; then
+    sigev_notify_thread_id=yes
+fi
+
 ##########################################
 # check if trace backend exists
 
@@ -5718,6 +5731,9 @@ fi
 if test "$st_atim" = "yes" ; then
   echo "HAVE_STRUCT_STAT_ST_ATIM=y" >> $config_host_mak
 fi
+if test "$sigev_notify_thread_id" = "yes" ; then
+  echo "HAVE_SIGEV_NOTIFY_THREAD_ID=y" >> $config_host_mak
+fi
 if test "$byteswap_h" = "yes" ; then
   echo "CONFIG_BYTESWAP_H=y" >> $config_host_mak
 fi
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index c9f812091c..63464f9a96 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7393,6 +7393,10 @@ static inline abi_long host_to_target_timex64(abi_long target_addr,
 }
 #endif
 
+#ifndef HAVE_SIGEV_NOTIFY_THREAD_ID
+#define sigev_notify_thread_id _sigev_un._tid
+#endif
+
 static inline abi_long target_to_host_sigevent(struct sigevent *host_sevp,
                                                abi_ulong target_addr)
 {
@@ -7413,7 +7417,7 @@ static inline abi_long target_to_host_sigevent(struct sigevent *host_sevp,
     host_sevp->sigev_signo =
         target_to_host_signal(tswap32(target_sevp->sigev_signo));
     host_sevp->sigev_notify = tswap32(target_sevp->sigev_notify);
-    host_sevp->_sigev_un._tid = tswap32(target_sevp->_sigev_un._tid);
+    host_sevp->sigev_notify_thread_id = tswap32(target_sevp->_sigev_un._tid);
 
     unlock_user_struct(target_sevp, target_addr, 1);
     return 0;
-- 
2.31.1