[glibc] Linux: Explicitly disable cancellation checking in the dynamic loader

[glibc] Linux: Explicitly disable cancellation checking in the dynamic loader

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1c75f89613a0b2428c21c19598559a2d64221cde

commit 1c75f89613a0b2428c21c19598559a2d64221cde
Author: Florian Weimer <fweimer@redhat.com>
Date:   Mon May 10 10:31:41 2021 +0200

    Linux: Explicitly disable cancellation checking in the dynamic loader
    
    Historically, SINGLE_THREAD_P is defined to 1 in the dynamic loader.
    This has the side effect of disabling cancellation points.  In order
    to enable future use of SINGLE_THREAD_P for single-thread
    optimizations in the dynamic loader (which becomes important once
    more code is moved from libpthread), introduce a new
    NO_SYSCALL_CANCEL_CHECKING macro which is always 1 for IS_IN (rtld),
    indepdently of the actual SINGLE_THREAD_P value.
    
    Tested-by: Carlos O'Donell <carlos@redhat.com>
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 sysdeps/unix/sysdep.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/sysdeps/unix/sysdep.h b/sysdeps/unix/sysdep.h
index 2fa6bfa135..664d093c05 100644
--- a/sysdeps/unix/sysdep.h
+++ b/sysdeps/unix/sysdep.h
@@ -88,10 +88,17 @@
 #define INLINE_SYSCALL_CALL(...) \
   __INLINE_SYSCALL_DISP (__INLINE_SYSCALL, __VA_ARGS__)
 
+#if IS_IN (rtld)
+/* All cancellation points are compiled out in the dynamic loader.  */
+# define NO_SYSCALL_CANCEL_CHECKING 1
+#else
+# define NO_SYSCALL_CANCEL_CHECKING SINGLE_THREAD_P
+#endif
+
 #define SYSCALL_CANCEL(...) \
   ({									     \
     long int sc_ret;							     \
-    if (SINGLE_THREAD_P) 						     \
+    if (NO_SYSCALL_CANCEL_CHECKING)					     \
       sc_ret = INLINE_SYSCALL_CALL (__VA_ARGS__); 			     \
     else								     \
       {									     \
@@ -107,7 +114,7 @@
 #define INTERNAL_SYSCALL_CANCEL(...) \
   ({									     \
     long int sc_ret;							     \
-    if (SINGLE_THREAD_P) 						     \
+    if (NO_SYSCALL_CANCEL_CHECKING) 					     \
       sc_ret = INTERNAL_SYSCALL_CALL (__VA_ARGS__); 			     \
     else								     \
       {									     \