nscd time_t size mismatch problem

[Zev Weiss]

Hello glibc devs,

We've recently been seeing some misbehavior from nscd in OpenBMC.  It
manifests as lots of log messages like:

     disabled inotify-based monitoring for file /passwd': No such file or directory
     stat failed for file /passwd'; will try again later: No such file or directory
     disabled inotify-based monitoring for file /group': No such file or directory
     stat failed for file /group'; will try again later: No such file or directory
     disabled inotify-based monitoring for file /hosts': No such file or directory
     stat failed for file /hosts'; will try again later: No such file or directory
     disabled inotify-based monitoring for file /resolv.conf': No such file or directory
     stat failed for file /resolv.conf'; will try again later: No such file or directory

and so forth.  I initially assumed it was a configure-time --sysconfdir 
mixup, but after digging into it I found that it actually stems from a 
time_t size mismatch (this is a 32-bit ARM gnueabi target):

     $ gdb -batch -ex 'pt time_t' -ex 'p sizeof(time_t)' time/time.o
     type = long
     $1 = 4
     $ gdb -batch -ex 'pt time_t' -ex 'p sizeof(time_t)' nscd/nscd.o
     type = long long
     $1 = 8

The confusing log messages are thus just the result of the coincidence 
that sizeof(long long) - sizeof(long) == strlen("/etc"), which causes 
the disagreement in the layout of struct traced_file to make it look 
like the 'fname' member just had its directory prefix chopped off.

In the discussion of the bug in the OpenBMC issue tracker [0], Wayne 
Tung (CCed) came up with the patch below, which does seem to solve the 
immediate problem, but if I'm understanding things right does so by just 
reverting nscd to a 32-bit time_t, and so I'd expect probably wouldn't 
be considered the "right" fix -- however I don't presently know enough 
about the 32/64-bit time_t transition and ensuing compatibility concerns 
to know what the right fix really is.  Should nscd perhaps be using 
__time64_t or something instead of time_t?


Thanks,
Zev Weiss

[0] https://github.com/openbmc/openbmc/issues/3881

 From 0fda9faf757abd4f5469e6d9207499e97f79a663 Mon Sep 17 00:00:00 2001
From: Wayne Tung <wayne.tung at ui.com>
Date: Thu, 13 Oct 2022 13:10:21 +0800
Subject: [PATCH] Use 32 bits time_t for ncsd

---
  Makeconfig | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makeconfig b/Makeconfig
index 47db08d6ae..f78f7cc74a 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -869,7 +869,7 @@ endif
  +extra-math-flags = $(if $(filter libm,$(in-module)),-fno-math-errno,-fmath-errno)

  # Use 64 bit time_t support for installed programs
-installed-modules = nonlib nscd lddlibc4 ldconfig locale_programs \
+installed-modules = nonlib lddlibc4 ldconfig locale_programs \
             iconvprogs libnss_files libnss_compat libnss_db libnss_hesiod \
             libutil libpcprofile libSegFault
  +extra-time-flags = $(if $(filter $(installed-modules),\
--