Re: [pushed] Block signals during the initial part of dlopen

[Florian Weimer <fw at deneb dot enyo dot de>]

* Joseph Myers:

> On Wed, 27 Nov 2019, Sourceware to Gerrit sync (Code Review) wrote:
>
>> Block signals during the initial part of dlopen
>> 
>> Lazy binding in a signal handler that interrupts a dlopen sees
>> intermediate dynamic linker state.  This has likely been always
>> unsafe, but with the new pending NODELETE state, this is clearly
>> incorrect.  Other threads are excluded via the loader lock, but the
>> current thread is not.  Blocking signals until right before ELF
>> constructors run is the safe thing to do.
>
> This change (commit a2e8aa0d9ea648068d8be52dd7b15f1b6a008e23) breaks the 
> build for i686-gnu (unfortunately this was after a syntax error was 
> introduced in build-many-glibcs.py so my bots quietly died on re-execing 
> with the syntax error, and so didn't get to find this build failure).
>
> There are a series of errors linking ld.so starting with:
>
> /scratch/jmyers/glibc/many9/install/compilers/i686-gnu/lib/gcc/i686-glibc-gnu/9.2.1/../../../../i686-glibc-gnu/bin/ld:
> /scratch/jmyers/glibc/many9/build/glibcs/i686-gnu/glibc/libc_pic.a(libc_fatal.os):
> in function `__GI___libc_fatal':
> /scratch/jmyers/glibc/many9/src/glibc/libio/../sysdeps/posix/libc_fatal.c:161:
> multiple definition of `__libc_fatal';
> /scratch/jmyers/glibc/many9/build/glibcs/i686-gnu/glibc/elf/dl-allobjs.os:/scratch/jmyers/glibc/many9/src/glibc/elf/dl-minimal.c:188:
> first defined here
>
> and leading up to:
>
> make[3]: ***
> [/scratch/jmyers/glibc/many9/build/glibcs/i686-gnu/glibc/elf/librtld.map]
> Error 1

I failed to test the later commits using build-many-glibcs.py because
I deemed them more straightforward.

The patch below should fix it.

8<------------------------------------------------------------------8<
hurd: Add stub implementation of __sigprocmask to the dynamic loader

The actual __sigprocmask cannot be built for the loader since it
depends on per-thread state.

diff --git a/sysdeps/mach/hurd/Versions b/sysdeps/mach/hurd/Versions
index f69d5fef67..57d45e6d0d 100644
--- a/sysdeps/mach/hurd/Versions
+++ b/sysdeps/mach/hurd/Versions
@@ -41,6 +41,6 @@ ld {
 
     # functions that must be shared with libc
     __access_noerrno; __libc_read; __libc_write; __libc_lseek64;
-    __libc_lock_self0;
+    __libc_lock_self0; __sigprocmask;
   }
 }
diff --git a/sysdeps/mach/hurd/dl-sysdep.c b/sysdeps/mach/hurd/dl-sysdep.c
index 719d603f44..e35ce69c4a 100644
--- a/sysdeps/mach/hurd/dl-sysdep.c
+++ b/sysdeps/mach/hurd/dl-sysdep.c
@@ -693,6 +693,15 @@ _hurd_intr_rpc_mach_msg (mach_msg_header_t *msg,
 		     timeout, notify);
 }
 
+/* This function does nothing and will be interposed with the actual
+   implementation once is libc is loaded.  Before that, manipulating
+   the signal mask does not make sense because no signal handlers have
+   been installed.  */
+int weak_function
+__sigprocmask (int how, const sigset_t *set, sigset_t *oset)
+{
+  return 0;
+}
 
 void
 _dl_show_auxv (void)