From: Sandra Loosemore <sandra@codesourcery.com>
Date: Thu, 21 Nov 2019 02:10:40 +0000 (-0700)
Subject: Compile elf/rtld.c with -fno-tree-loop-distribute-patterns.
X-Git-Tag: glibc-2.31~222
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c72e5cd87dcb075782f9b6beea024b984f2e1130;p=thirdparty%2Fglibc.git

Compile elf/rtld.c with -fno-tree-loop-distribute-patterns.

In GCC 10, the default at -O2 is now -ftree-loop-distribute-patterns.
This optimization causes GCC to "helpfully" convert the hand-written
loop in _dl_start into a call to memset, which is not available that
early in program startup.  Similar problems in other places in GLIBC
have been addressed by explicitly building with
-fno-tree-loop-distribute-patterns, but this one may have been
overlooked previously because it only affects targets where
HAVE_BUILTIN_MEMSET is not defined.

This patch fixes a bug observed on nios2-linux-gnu target that caused
all programs to segv on startup.
---

diff --git a/elf/Makefile b/elf/Makefile
index 06688181e3e..b05af5ce3a2 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -65,6 +65,12 @@ CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables
 CFLAGS-dl-lookup.c += -fexceptions -fasynchronous-unwind-tables
 CFLAGS-dl-iterate-phdr.c += $(uses-callbacks)
 
+# On targets without __builtin_memset, rtld.c uses a hand-coded loop
+# in _dl_start.  Make sure this isn't turned into a call to regular memset.
+ifeq (yes,$(have-loop-to-function))
+CFLAGS-rtld.c += -fno-tree-loop-distribute-patterns
+endif
+
 # Compile rtld itself without stack protection.
 # Also compile all routines in the static library that are elided from
 # the shared libc because they are in libc.a in the same way.