[3/4] MSP430: Disable __cxa_atexit

Message ID 20191107213914.5fcd8a21@jozef-kubuntu
State New
Headers show
Series
  • Tweaks to default configuration to reduce code size
Related show

Commit Message

Jozef Lawrynowicz Nov. 7, 2019, 9:39 p.m.
The MSP430 target does not need to support dynamic shared objects so
__cxa_atexit does not need to be used - atexit is sufficient.

Newlib atexit is a fine replacement as it also supports registration of more
than 32 functions.

By not using __cxa_atexit, we can define TARGET_LIBGCC_REMOVE_DSO_HANDLE to
remove the definition of __dso_handle from crtstuff.c, saving code size by
removing the necessity to link in functions to initialize global data in
*every* program.

Patch

From a0086b73d0e029c8888ab2f65a91e67a2502e4d4 Mon Sep 17 00:00:00 2001
From: Jozef Lawrynowicz <jozef.l@mittosystems.com>
Date: Wed, 30 Oct 2019 16:39:52 +0000
Subject: [PATCH 3/4] MSP430: Disable __cxa_atexit

gcc/ChangeLog:

2019-11-07  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* config.gcc (msp430*-*-*): Disable __cxa_atexit by default.
	* config/msp430/msp430.c (msp430_option_override): Emit an error if
	-fuse-cxa-atexit was used when __cxa_atexit was disabled at configure
	time.
	* config/msp430/msp430.h (TARGET_LIBGCC_REMOVE_DSO_HANDLE): Define if
	__cxa_atexit was disabled at configure time.
	
gcc/testsuite/ChangeLog:

2019-11-07  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* g++.dg/init/dso_handle1.C: Add dg-require-cxa-atexit. 
	* g++.dg/init/dso_handle2.C: Likewise.
	* g++.dg/other/cxa-atexit1.C: Likewise.
	* lib/target-supports.exp (check_cxa_atexit_available): Add hard-coded
	case for msp430.

---
 gcc/config.gcc                           | 7 +++++++
 gcc/config/msp430/msp430.c               | 9 +++++++++
 gcc/config/msp430/msp430.h               | 6 ++++++
 gcc/testsuite/g++.dg/init/dso_handle1.C  | 1 +
 gcc/testsuite/g++.dg/init/dso_handle2.C  | 1 +
 gcc/testsuite/g++.dg/other/cxa-atexit1.C | 1 +
 gcc/testsuite/lib/target-supports.exp    | 3 +++
 7 files changed, 28 insertions(+)

diff --git a/gcc/config.gcc b/gcc/config.gcc
index d74bcbb9856..2e79101cc8f 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -2533,6 +2533,13 @@  msp430*-*-*)
 	tmake_file="${tmake_file} msp430/t-msp430"
 	extra_objs="${extra_objs} msp430-devices.o"
 	extra_gcc_objs="driver-msp430.o msp430-devices.o"
+
+	# __cxa_atexit increases code size, and we don't need to support dynamic
+	# shared objects on MSP430, so regular Newlib atexit is a fine
+	# replacement as it also supports registration of more than 32
+	# functions.
+	default_use_cxa_atexit=no
+
 	# Enable .init_array unless it has been explicitly disabled.
 	# The MSP430 EABI mandates the use of .init_array, and the Newlib CRT
 	# code since mid-2019 expects it.
diff --git a/gcc/config/msp430/msp430.c b/gcc/config/msp430/msp430.c
index fe1fcc0db43..ce8d863abd3 100644
--- a/gcc/config/msp430/msp430.c
+++ b/gcc/config/msp430/msp430.c
@@ -284,6 +284,15 @@  msp430_option_override (void)
      possible to build newlib with -Os enabled.  Until now...  */
   if (TARGET_OPT_SPACE && optimize < 3)
     optimize_size = 1;
+
+#if !DEFAULT_USE_CXA_ATEXIT
+  /* By default, we enforce atexit() instead of __cxa_atexit() to save on code
+     size and remove the declaration of __dso_handle from the CRT library.
+     Configuring GCC with --enable-__cxa-atexit re-enables it by defining
+     DEFAULT_USE_CXA_ATEXIT to 1.  */
+  if (flag_use_cxa_atexit)
+    error ("%<-fuse-cxa-atexit%> is not supported for msp430-elf");
+#endif
 }
 
 #undef  TARGET_SCALAR_MODE_SUPPORTED_P
diff --git a/gcc/config/msp430/msp430.h b/gcc/config/msp430/msp430.h
index 90ceec0e947..25944125182 100644
--- a/gcc/config/msp430/msp430.h
+++ b/gcc/config/msp430/msp430.h
@@ -509,4 +509,10 @@  typedef struct
 #define ASM_OUTPUT_ALIGNED_DECL_COMMON(FILE, DECL, NAME, SIZE, ALIGN)	\
   msp430_output_aligned_decl_common ((FILE), (DECL), (NAME), (SIZE), (ALIGN))
 
+#if !DEFAULT_USE_CXA_ATEXIT
+/* We're not using __cxa_atexit, so __dso_handle isn't needed.  */
+#undef TARGET_LIBGCC_REMOVE_DSO_HANDLE
+#define TARGET_LIBGCC_REMOVE_DSO_HANDLE
+#endif
+
 #define SYMBOL_FLAG_LOW_MEM (SYMBOL_FLAG_MACH_DEP << 0)
diff --git a/gcc/testsuite/g++.dg/init/dso_handle1.C b/gcc/testsuite/g++.dg/init/dso_handle1.C
index 97f67cad8f4..dc92e22d12a 100644
--- a/gcc/testsuite/g++.dg/init/dso_handle1.C
+++ b/gcc/testsuite/g++.dg/init/dso_handle1.C
@@ -1,6 +1,7 @@ 
 // PR c++/17042
 // { dg-do assemble }
 /* { dg-require-weak "" } */
+// { dg-require-cxa-atexit "" }
 // { dg-options "-fuse-cxa-atexit" }
 
 struct A
diff --git a/gcc/testsuite/g++.dg/init/dso_handle2.C b/gcc/testsuite/g++.dg/init/dso_handle2.C
index b219dc02611..6e151e50fa7 100644
--- a/gcc/testsuite/g++.dg/init/dso_handle2.C
+++ b/gcc/testsuite/g++.dg/init/dso_handle2.C
@@ -1,4 +1,5 @@ 
 // PR c++/58846
+// { dg-require-cxa-atexit "" }
 // { dg-options "-fuse-cxa-atexit" }
 
 extern "C" { char* __dso_handle; }
diff --git a/gcc/testsuite/g++.dg/other/cxa-atexit1.C b/gcc/testsuite/g++.dg/other/cxa-atexit1.C
index a51f3340142..d6ab3dc4733 100644
--- a/gcc/testsuite/g++.dg/other/cxa-atexit1.C
+++ b/gcc/testsuite/g++.dg/other/cxa-atexit1.C
@@ -1,4 +1,5 @@ 
 // { dg-do compile }
+// { dg-require-cxa-atexit "" }
 // { dg-options "-O2 -fuse-cxa-atexit" }
 
 # 1 "cxa-atexit1.C"
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 6c836a4accc..58bedb64d42 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -2513,6 +2513,9 @@  proc check_cxa_atexit_available { } {
 	} elseif { [istarget *-*-vxworks] } {
 	    # vxworks doesn't have __cxa_atexit but subsequent test passes.
 	    expr 0
+	} elseif { [istarget msp430-*-*] } {
+	    # msp430 doesn't have __cxa_atexit but subsequent test passes.
+	    expr 0
 	} else {
 	    check_runtime_nocache cxa_atexit_available {
 		// C++
-- 
2.17.1