elf: Rework exception handling in the dynamic loader [BZ #25486]

The old exception handling implementation used function interposition
to replace the dynamic loader implementation (no TLS support) with the
libc implementation (TLS support).  This results in problems if the
link order between the dynamic loader and libc is reversed (bug 25486).

The new implementation moves the entire implementation of the
exception handling functions back into the dynamic loader, using
THREAD_GETMEM and THREAD_SETMEM for thread-local data support.
These depends on Hurd support for these macros, added in commit
b65a82e4e757c1e6cb7073916 ("hurd: Add THREAD_GET/SETMEM/_NC").

One small obstacle is that the exception handling facilities are used
before the TCB has been set up, so a check is needed if the TCB is
available.  If not, a regular global variable is used to store the
exception handling information.

Also rename dl-error.c to dl-catch.c, to avoid confusion with the
dlerror function.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

1 files changed, 1 insertions, 7 deletions

diff --git a/elf/Versions b/elf/Versions
index a9ff278de7..4614acea3e 100644
--- a/elf/Versions
+++ b/elf/Versions
@@ -31,10 +31,6 @@ libc {
   GLIBC_PRIVATE {
     # functions used in other libraries
     __libc_early_init;
-
-    # Internal error handling support.  Interposes the functions in ld.so.
-    _dl_signal_exception; _dl_catch_exception;
-    _dl_signal_error; _dl_catch_error;
   }
 }
 
@@ -77,10 +73,8 @@ ld {
 
     # Internal error handling support.
     _dl_exception_create; _dl_exception_create_format; _dl_exception_free;
-
-    # Internal error handling support.  Interposed by libc.so.
     _dl_signal_exception; _dl_catch_exception;
-    _dl_signal_error; _dl_catch_error;
+    _dl_signal_error;
 
     # Set value of a tunable.
     __tunable_get_val;