An annoying wart with debugging the plugin is that attempts to set
a breakpoint on a function set two breakpoints: on the "funcname@plt",
and on the function itself, making stepping through the code more
awkward than it ought to be.
This patch detects for -fno-semantic-interposition at configure
time, and adds it to PLUGIN_CFLAGS if available, eliminating the
"funcname@plt" entries.
Presumably this also speeds up in-tree plugin code.
Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
Pushed to branch "dmalcolm/analyzer" on the GCC git mirror,
along with the autogenerated changes to gcc/configure as a followup
gcc/ChangeLog:
* Makefile.in (SEM_INTERPOS_FLAGS): New.
(PLUGIN_CFLAGS): Flesh out comment. Add SEM_INTERPOS_FLAGS.
* configure.ac (sem_interpos_flags): Add this, testing for
-fno-semantic-interposition.
---
gcc/Makefile.in | 16 ++++++++++++++--
gcc/configure.ac | 12 ++++++++++++
2 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 0587447..224bd75 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -188,6 +188,8 @@ NOEXCEPTION_FLAGS = @noexception_flags@
ALIASING_FLAGS = @aliasing_flags@
+SEM_INTERPOS_FLAGS = @sem_interpos_flags@
+
# This is set by --disable-maintainer-mode (default) to "#"
# FIXME: 'MAINT' will always be set to an empty string, no matter if
# --disable-maintainer-mode is used or not. This is because the
@@ -1786,8 +1788,18 @@ ifneq ($(PLUGIN_MAKEFRAGS),)
include $(PLUGIN_MAKEFRAGS)
endif
-# Add PLUGIN_CFLAGS to objects that belong to in-tree plugins
-PLUGIN_CFLAGS = -fPIC
+# Define PLUGIN_CFLAGS and add it to objects that belong to in-tree plugins
+#
+# .o files for plugins need to built as position-independent code, hence -fPIC
+#
+# We use -fno-semantic-interposition if available (via SEM_INTERPOS_FLAGS)
+# since it fixes an annoying wart when debugging the plugin, where every
+# attempt to set a breakpoint on a function sets two breakpoints: on the
+# "funcname@plt", and on the function itself, making stepping through the
+# code more awkward than it ought to be. Presumably this also leads
+# to faster plugin code.
+
+PLUGIN_CFLAGS = -fPIC $(SEM_INTERPOS_FLAGS)
$(foreach file,$(ALL_HOST_PLUGIN_OBJS),$(eval CFLAGS-$(file) +=
$(PLUGIN_CFLAGS)))
#
diff --git a/gcc/configure.ac b/gcc/configure.ac
index ff6023e..eb30857 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -461,7 +461,19 @@ if test "$GCC" = yes; then
fi
AC_SUBST(aliasing_flags)
+sem_interpos_flags=
+if test "$GCC" = yes; then
+ saved_CXXFLAGS="$CXXFLAGS"
+
+ CXXFLAGS="$CXXFLAGS -fno-semantic-interposition"
+ AC_MSG_CHECKING(whether the compiler supports -fno-semantic-interposition)
+ AC_COMPILE_IFELSE([AC_LANG_SOURCE([])],
+ [AC_MSG_RESULT([yes]); sem_interpos_flags='-fno-semantic-interposition'],
+ [AC_MSG_RESULT([no])])
+ CXXFLAGS="$saved_CXXFLAGS"
+fi
+AC_SUBST(sem_interpos_flags)
# ---------------------
# Warnings and checking
--
1.8.5.3
