[1/3] libgcc: Add --disable-eh-frame-registry configure option

Message ID 20191106161627.0cd62fdf@jozef-kubuntu
State New
Headers show
Series
  • libgcc/crtstuff.c tweaks to reduce code size
Related show

Commit Message

Jozef Lawrynowicz Nov. 6, 2019, 4:16 p.m.
The attached patch enables the EH Frame Registry to be explicitly disabled
with a configure option "-disable-eh-frame-registry", thereby removing code to
support it in crtstuff.c

Default behaviour is unchanged since USE_EH_FRAME_REGISTRY was previously
referenced only internally in crtstuff.c, and now is only defined to 0
when it would previously have not been defined at all.

Comments

Jozef Lawrynowicz Nov. 6, 2019, 9:05 p.m. | #1
On Wed, 6 Nov 2019 16:16:27 +0000
Jozef Lawrynowicz <jozef.l@mittosystems.com> wrote:

> The attached patch enables the EH Frame Registry to be explicitly disabled

> with a configure option "-disable-eh-frame-registry", thereby removing code to

> support it in crtstuff.c

> 

> Default behaviour is unchanged since USE_EH_FRAME_REGISTRY was previously

> referenced only internally in crtstuff.c, and now is only defined to 0

> when it would previously have not been defined at all.


I retract this patch, since I have found a better solution to the problem this
was going to solve.

Passing "-U__LIBGCC_EH_FRAME_SECTION_NAME__" when building crtstuff.c objects
completely removes references to .eh_frame.

The original patch still resulted in the .eh_frame section being created,
since code to add a 4byte NULL sentinel to the end of the section was retained.

If someone thinks the original patch might still be useful, I can go ahead and
commit it anyway.

Patch

From 31fdea3564fd0a9a25547df0d5052133d7bdc8a6 Mon Sep 17 00:00:00 2001
From: Jozef Lawrynowicz <jozef.l@mittosystems.com>
Date: Tue, 29 Oct 2019 12:55:11 +0000
Subject: [PATCH 1/3] libgcc: Add --disable-eh-frame-registry configure option

gcc/ChangeLog:

2019-11-06  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* doc/install.texi: Document --disable-eh-frame-registry.

libgcc/ChangeLog:

2019-11-06  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* Makefile.in: Add USE_EH_FRAME_REGISTRY variable.
	Use USE_EH_FRAME_REGISTRY variable in CRTSTUFF_CFLAGS. 
	* configure: Regenerate.
	* configure.ac: Support --disable-eh-frame-registry.
	* crtstuff.c [!USE_EH_FRAME_REGISTRY]: Define USE_EH_FRAME_REGISTRY.
	s/#ifdef USE_EH_FRAME_REGISTRY/#if USE_EH_FRAME_REGISTRY/.
	s/#if defined(USE_EH_FRAME_REGISTRY)/#if USE_EH_FRAME_REGISTRY/.

---
 gcc/doc/install.texi | 11 +++++++++++
 libgcc/Makefile.in   |  4 +++-
 libgcc/configure     | 22 ++++++++++++++++++++++
 libgcc/configure.ac  | 17 +++++++++++++++++
 libgcc/crtstuff.c    | 22 +++++++++++++---------
 5 files changed, 66 insertions(+), 10 deletions(-)

diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
index 563de705881..af61a34a477 100644
--- a/gcc/doc/install.texi
+++ b/gcc/doc/install.texi
@@ -1314,6 +1314,17 @@  Disable TM clone registry in libgcc. It is enabled in libgcc by default.
 This option helps to reduce code size for embedded targets which do
 not use transactional memory.
 
+@item --disable-eh-frame-registry
+Disable the EH frame registry in libgcc.  It is enabled in libgcc by default
+for most ELF targets.
+
+This should not be used unless exceptions have been disabled for the target
+configuration.
+
+This option reduces code size by removing functionality to register the
+exception handling frame information that would normally run before
+@samp{main()}.
+
 @item --with-cpu=@var{cpu}
 @itemx --with-cpu-32=@var{cpu}
 @itemx --with-cpu-64=@var{cpu}
diff --git a/libgcc/Makefile.in b/libgcc/Makefile.in
index 5608352a900..59f7f3cc381 100644
--- a/libgcc/Makefile.in
+++ b/libgcc/Makefile.in
@@ -261,6 +261,8 @@  CET_FLAGS = @CET_FLAGS@
 
 USE_TM_CLONE_REGISTRY = @use_tm_clone_registry@
 
+USE_EH_FRAME_REGISTRY = @use_eh_frame_registry@
+
 # Defined in libgcc2.c, included only in the static library.
 LIB2FUNCS_ST = _eprintf __gcc_bcmp
 
@@ -301,7 +303,7 @@  CRTSTUFF_CFLAGS = -O2 $(GCC_CFLAGS) $(INCLUDES) $(MULTILIB_CFLAGS) -g0 \
   $(NO_PIE_CFLAGS) -finhibit-size-directive -fno-inline -fno-exceptions \
   -fno-zero-initialized-in-bss -fno-toplevel-reorder -fno-tree-vectorize \
   -fbuilding-libgcc -fno-stack-protector $(FORCE_EXPLICIT_EH_REGISTRY) \
-  $(INHIBIT_LIBC_CFLAGS) $(USE_TM_CLONE_REGISTRY)
+  $(INHIBIT_LIBC_CFLAGS) $(USE_TM_CLONE_REGISTRY) $(USE_EH_FRAME_REGSITRY)
 
 # Extra flags to use when compiling crt{begin,end}.o.
 CRTSTUFF_T_CFLAGS =
diff --git a/libgcc/configure b/libgcc/configure
index 117e9c97e57..341c609252e 100755
--- a/libgcc/configure
+++ b/libgcc/configure
@@ -605,6 +605,7 @@  solaris_ld_v2_maps
 real_host_noncanonical
 accel_dir_suffix
 use_tm_clone_registry
+use_eh_frame_registry
 force_explicit_eh_registry
 CET_FLAGS
 fixed_point
@@ -713,6 +714,7 @@  enable_decimal_float
 with_system_libunwind
 enable_cet
 enable_explicit_exception_frame_registration
+enable_eh_frame_registry
 enable_tm_clone_registry
 with_glibc_version
 enable_tls
@@ -1357,6 +1359,7 @@  Optional Features:
                           register exception tables explicitly at module
                           start, for use e.g. for compatibility with
                           installations without PT_GNU_EH_FRAME support
+  --disable-eh-frame-registry    disable EH frame registry
   --disable-tm-clone-registry    disable TM clone registry
   --enable-tls            Use thread-local storage [default=yes]
 
@@ -4956,6 +4959,25 @@  fi
 
 
 
+# EH Frame Registry is implicitly enabled by default (although it is not
+# "forced"), and libgcc/crtstuff.c will setup the support for it if it is
+# supported by the target.  So we don't handle --enable-eh-frame-registry.
+# Check whether --enable-eh-frame-registry was given.
+if test "${enable_eh_frame_registry+set}" = set; then :
+  enableval=$enable_eh_frame_registry;
+use_eh_frame_registry=
+if test "$enable_eh_frame_registry" = no; then
+  if test "$enable_explicit_exception_frame_registration" = yes; then
+    as_fn_error $? "Can't --disable-eh-frame-registry with
+		  with --enable-explicit-exception-frame-registration" "$LINENO" 5
+  fi
+  use_eh_frame_registry=-DUSE_EH_FRAME_REGISTRY=0
+fi
+
+fi
+
+
+
 # Check whether --enable-tm-clone-registry was given.
 if test "${enable_tm_clone_registry+set}" = set; then :
   enableval=$enable_tm_clone_registry;
diff --git a/libgcc/configure.ac b/libgcc/configure.ac
index f63c5e736e5..cf2eb9c984a 100644
--- a/libgcc/configure.ac
+++ b/libgcc/configure.ac
@@ -261,6 +261,23 @@  fi
 ])
 AC_SUBST([force_explicit_eh_registry])
 
+# EH Frame Registry is implicitly enabled by default (although it is not
+# "forced"), and libgcc/crtstuff.c will setup the support for it if it is
+# supported by the target.  So we don't handle --enable-eh-frame-registry.
+AC_ARG_ENABLE([eh-frame-registry],
+[  --disable-eh-frame-registry    disable EH frame registry],
+[
+use_eh_frame_registry=
+if test "$enable_eh_frame_registry" = no; then
+  if test "$enable_explicit_exception_frame_registration" = yes; then
+    AC_MSG_ERROR([Can't --disable-eh-frame-registry with
+		  with --enable-explicit-exception-frame-registration])
+  fi
+  use_eh_frame_registry=-DUSE_EH_FRAME_REGISTRY=0
+fi
+])
+AC_SUBST([use_eh_frame_registry])
+
 AC_ARG_ENABLE([tm-clone-registry],
 [  --disable-tm-clone-registry    disable TM clone registry],
 [
diff --git a/libgcc/crtstuff.c b/libgcc/crtstuff.c
index ae6328d317d..9a3247b7848 100644
--- a/libgcc/crtstuff.c
+++ b/libgcc/crtstuff.c
@@ -136,9 +136,13 @@  call_ ## FUNC (void)					\
 #  error "Can't use explicit exception-frame-registration without __LIBGCC_EH_FRAME_SECTION_NAME__"
 # endif
 #endif
+#ifndef USE_EH_FRAME_REGISTRY
 #if defined(__LIBGCC_EH_FRAME_SECTION_NAME__) && (!defined(USE_PT_GNU_EH_FRAME) || defined(USE_EH_FRAME_REGISTRY_ALWAYS))
-# define USE_EH_FRAME_REGISTRY
+# define USE_EH_FRAME_REGISTRY 1
+#else
+# define USE_EH_FRAME_REGISTRY 0
 #endif
+#endif /* USE_EH_FRAME_REGISTRY */
 #if defined(__LIBGCC_EH_FRAME_SECTION_NAME__) \
     && __LIBGCC_EH_TABLES_CAN_BE_READ_ONLY__
 # define EH_FRAME_SECTION_CONST const
@@ -257,7 +261,7 @@  STATIC func_ptr __DTOR_LIST__[1]
 #endif /* __DTOR_LIST__ alternatives */
 #endif /* USE_INITFINI_ARRAY */
 
-#ifdef USE_EH_FRAME_REGISTRY
+#if USE_EH_FRAME_REGISTRY
 /* Stick a label at the beginning of the frame unwind info so we can register
    and deregister it with the exception handling library code.  */
 STATIC EH_FRAME_SECTION_CONST char __EH_FRAME_BEGIN__[]
@@ -412,7 +416,7 @@  __do_global_dtors_aux (void)
   deregister_tm_clones ();
 #endif /* USE_TM_CLONE_REGISTRY */
 
-#ifdef USE_EH_FRAME_REGISTRY
+#if USE_EH_FRAME_REGISTRY
 #ifdef CRT_GET_RFIB_DATA
   /* If we used the new __register_frame_info_bases interface,
      make sure that we deregister from the same place.  */
@@ -452,7 +456,7 @@  CRT_CALL_STATIC_FUNCTION (__LIBGCC_INIT_SECTION_ASM_OP__,
 			  __do_global_dtors_aux_1)
 #endif
 
-#if defined(USE_EH_FRAME_REGISTRY) || USE_TM_CLONE_REGISTRY
+#if USE_EH_FRAME_REGISTRY || USE_TM_CLONE_REGISTRY
 /* Stick a call to __register_frame_info into the .init section.  For some
    reason calls with no arguments work more reliably in .init, so stick the
    call in another function.  */
@@ -460,7 +464,7 @@  CRT_CALL_STATIC_FUNCTION (__LIBGCC_INIT_SECTION_ASM_OP__,
 static void __attribute__((used))
 frame_dummy (void)
 {
-#ifdef USE_EH_FRAME_REGISTRY
+#if USE_EH_FRAME_REGISTRY
   static struct object object;
 #ifdef CRT_GET_RFIB_DATA
   void *tbase, *dbase;
@@ -555,13 +559,13 @@  __do_global_dtors (void)
   deregister_tm_clones ();
 #endif /* USE_TM_CLONE_REGISTRY */
 
-#ifdef USE_EH_FRAME_REGISTRY
+#if USE_EH_FRAME_REGISTRY
   if (__deregister_frame_info)
     __deregister_frame_info (__EH_FRAME_BEGIN__);
 #endif
 }
 
-#if defined(USE_EH_FRAME_REGISTRY) || USE_TM_CLONE_REGISTRY
+#if USE_EH_FRAME_REGISTRY || USE_TM_CLONE_REGISTRY
 /* A helper function for __do_global_ctors, which is in crtend.o.  Here
    in crtbegin.o, we can reference a couple of symbols not visible there.
    Plus, since we're before libgcc.a, we have no problems referencing
@@ -569,7 +573,7 @@  __do_global_dtors (void)
 void
 __do_global_ctors_1(void)
 {
-#ifdef USE_EH_FRAME_REGISTRY
+#if USE_EH_FRAME_REGISTRY
   static struct object object;
   if (__register_frame_info)
     __register_frame_info (__EH_FRAME_BEGIN__, &object);
@@ -733,7 +737,7 @@  void
 __do_global_ctors (void)
 {
   func_ptr *p;
-#if defined(USE_EH_FRAME_REGISTRY) || USE_TM_CLONE_REGISTRY
+#if USE_EH_FRAME_REGISTRY || USE_TM_CLONE_REGISTRY
   __do_global_ctors_1();
 #endif
   for (p = __CTOR_END__ - 1; *p != (func_ptr) -1; p--)
-- 
2.17.1