Ruby: wrap calls to memcpy so that gem is compatible with pre-2.14 glibc

This commit adds a __wrap_memcpy function and a linker flag to use that
in place of memcpy for our Ruby gem C extension. This allows us to
always use the 2.2.5 version of memcpy, making it possible to use the
gem on distributions with pre-2.14 versions of glibc.

Before this change:
$ objdump -T protobuf_c.so | grep memcpy
0000000000000000      DF *UND*  0000000000000000  GLIBC_2.3.4 __memcpy_chk
0000000000000000      DF *UND*  0000000000000000  GLIBC_2.14  memcpy

After:
$ objdump -T protobuf_c.so | grep memcpy
0000000000000000      DF *UND*  0000000000000000  GLIBC_2.2.5 memcpy
0000000000000000      DF *UND*  0000000000000000  GLIBC_2.3.4 __memcpy_chk
0000000000042450 g    DF .text  0000000000000005  Base __wrap_memcpy

This is based on gRPC's solution to a similar problem:
https://github.com/grpc/grpc/blob/5098508d2d41a116113f7e333c516cd9ef34a943/src/core/lib/support/wrap_memcpy.c

This fixes issue #2783.

1 files changed, 8 insertions, 1 deletions

diff --git a/ruby/ext/google/protobuf_c/extconf.rb b/ruby/ext/google/protobuf_c/extconf.rb
index b368dcc6..0886e607 100644
--- a/ruby/ext/google/protobuf_c/extconf.rb
+++ b/ruby/ext/google/protobuf_c/extconf.rb
@@ -4,7 +4,14 @@ require 'mkmf'
 
 $CFLAGS += " -std=c99 -O3 -DNDEBUG"
 
+
+if RUBY_PLATFORM =~ /linux/
+  # Instruct the linker to point memcpy calls at our __wrap_memcpy wrapper.
+  $LDFLAGS += " -Wl,-wrap,memcpy"
+end
+
 $objs = ["protobuf.o", "defs.o", "storage.o", "message.o",
-         "repeated_field.o", "map.o", "encode_decode.o", "upb.o"]
+         "repeated_field.o", "map.o", "encode_decode.o", "upb.o",
+         "wrap_memcpy.o"]
 
 create_makefile("google/protobuf_c")