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gcc: Enable __cxa_atexit for final GCC

PATCH New Alexey Brodkin 4 participants 6 messages Nov 15, 2018

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Alexey Brodkin

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#0 lore raw

PATCH 1/1 gcc: Enable __cxa_atexit for final GCC

This is what GCC manual says [1]:
-------------------------->8---------------------- --enable-__cxa_atexit

Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects.

This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc.

This option is currently only available on systems with GNU libc
...
-------------------------->8----------------------

Important disadvantages of a simple atexit() are that [2]:
-------------------------->8----------------------
1999 C Standard only requires that the implementation support 32 registered functions, although most implementations support many more.

More important it does not deal at all with the ability in most implementations to remove DSOs from a running program image by calling dlclose prior to program termination. -------------------------->8----------------------

Essentially for initial GCC there's no point in enabling that feature as we're not going to build CPP applications wit hit.

Also it seems like all libc's we support in Buildroot (Glibc, uClibc and musl) support __cxa_at_exit() so enable it unconditionally.

[1] https://gcc.gnu.org/install/configure.html
[2] https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor-motivation

Signed-off-by Alexey Brodkin <[email protected]>
Cc Thomas Petazzoni <[email protected]>
Cc Mark Corbin <[email protected]>
Cc Romain Naour <[email protected]>
Cc Peter Korsgaard <[email protected]>
Cc Bernd Kuhls <[email protected]>
Cc Claudiu Zissulescu <[email protected]>
Cc Cupertino Miranda <[email protected]>
Cc Vineet Gupta <[email protected]>
---
 package/gcc/gcc-initial/gcc-initial.mk | 1 +
 package/gcc/gcc.mk                     | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
package/gcc/gcc-initial/gcc-initial.mk +1 -0
index d5d925a3d9..745a85607a 100644
@@ -40,6 +40,7 @@ HOST_GCC_INITIAL_CONF_OPTS = \
 	--with-newlib \
 	--disable-largefile \
 	--disable-nls \
+	--disable-__cxa_atexit \
 	$(call qstrip,$(BR2_EXTRA_GCC_CONFIG_OPTIONS))
 
 HOST_GCC_INITIAL_CONF_ENV = \
package/gcc/gcc.mk +1 -1
index e47435677e..5901624ea5 100644
@@ -87,7 +87,7 @@ HOST_GCC_COMMON_DEPENDENCIES = \
 HOST_GCC_COMMON_CONF_OPTS = \
 	--target=$(GNU_TARGET_NAME) \
 	--with-sysroot=$(STAGING_DIR) \
-	--disable-__cxa_atexit \
+	--enable-__cxa_atexit \
 	--with-gnu-ld \
 	--disable-libssp \
 	--disable-multilib \
Signature · 1 line
2.16.2
#1 lore raw

PATCH 1/1 gcc: Enable __cxa_atexit for final GCC

Quoted 10 lines · Alexey Brodkin

This is what GCC manual says [1]:
-------------------------->8---------------------- --enable-__cxa_atexit

Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects.

This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc.

For what is is worth, we enabled cxa_atexit in BR2_EXTRA_GCC_CONFIG_OPTIONS five years ago, to fix a crash that occurred when catching exceptions and logging them using a log system that used global variables. But we couldn't remember the details.

author
#2 lore raw

PATCH 1/1 gcc: Enable __cxa_atexit for final GCC

Hi Nicolas,

Quoted 8 lines · Nicolas Cavallari
Quoted 7 lines · Alexey Brodkin

This is what GCC manual says [1]:
-------------------------->8---------------------- --enable-__cxa_atexit

Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects.

Quoted 8 lines
Quoted 3 lines

This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc.

For what is is worth, we enabled cxa_atexit in BR2_EXTRA_GCC_CONFIG_OPTIONS five years ago, to fix a crash that occurred when catching exceptions and logging them using a log system that used global variables. But we couldn't remember the details.

So you've been using BR with cxa_atexit since then, right?
Or you mean it was enabled in upstream BR for some time and then reverted back to disabled state?

-Alexey

#3 lore raw

PATCH 1/1 gcc: Enable __cxa_atexit for final GCC

Hi Alexey,

Le 15/11/2018 ? 11:22, Alexey Brodkin a ?crit?:

Quoted 15 lines

Hi Nicolas,

Quoted 12 lines · Nicolas Cavallari
Quoted 10 lines · Alexey Brodkin

This is what GCC manual says [1]:
-------------------------->8---------------------- --enable-__cxa_atexit

Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects.

This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc.

Quoted 7 lines
Quoted 4 lines

For what is is worth, we enabled cxa_atexit in BR2_EXTRA_GCC_CONFIG_OPTIONS five years ago, to fix a crash that occurred when catching exceptions and logging them using a log system that used global variables. But we couldn't remember the details.

So you've been using BR with cxa_atexit since then, right?
Or you mean it was enabled in upstream BR for some time and then reverted back to disabled state?

--disable-__cxa_atexit is present since 2002/2003 in Buildroot, I'm not sure the reason for disabling atexit is still relevant.

Best regards,
Romain

Quoted 7 lines

-Alexey
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buildroot at busybox.net
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author
#4 lore raw

PATCH 1/1 gcc: Enable __cxa_atexit for final GCC

Hi Romain,

Quoted 23 lines · Romain Naour

Hi Alexey,

Le 15/11/2018 ? 11:22, Alexey Brodkin a ?crit :

Quoted 20 lines

Hi Nicolas,

Quoted 16 lines · Nicolas Cavallari
Quoted 10 lines · Alexey Brodkin

This is what GCC manual says [1]:
-------------------------->8---------------------- --enable-__cxa_atexit

Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects.

This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc.

For what is is worth, we enabled cxa_atexit in BR2_EXTRA_GCC_CONFIG_OPTIONS five years ago, to fix a crash that occurred when catching exceptions and logging them using a log system that used global variables. But we couldn't remember the details.

Quoted 5 lines
Quoted 2 lines

So you've been using BR with cxa_atexit since then, right?
Or you mean it was enabled in upstream BR for some time and then reverted back to disabled state?

--disable-__cxa_atexit is present since 2002/2003 in Buildroot, I'm not sure the reason for disabling atexit is still relevant.

For me there was a reason to get cxa_atexit enabled - SEGFAULT in one of Glibc tests on ARC so I do it it solves something as for whih problems that change might introduce I have no ideas :)

I did a build test with all libc's for x86 but nothing more serious.

Also if we look around we'll see
1. In OpenEmbedded it is enabled for everything except gcc-cross-initial:
https://github.com/openembedded/openembedded-core/blob/master/meta/recipes-devtools/gcc/gcc-configure-common.inc#L59
https://github.com/openembedded/openembedded-core/blob/master/meta/recipes-devtools/gcc/gcc-cross-initial.inc#L23

2. In Crosstool-NG it is enabled by default:
https://github.com/crosstool-ng/crosstool-ng/blob/master/config/cc/gcc.in#L270

3. In OpenWrt it is disabled only for uClibc, otherwise enabled:
https://github.com/openwrt/openwrt/blob/master/toolchain/gcc/common.mk#L170

So I think it looks promising.

-Alexey

#5 lore raw

PATCH 1/1 gcc: Enable __cxa_atexit for final GCC

In reply to Alexey Brodkin
Quoted 19 lines · Alexey Brodkin

This is what GCC manual says [1]:
-------------------------->8---------------------- --enable-__cxa_atexit

Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects.

This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc.

This option is currently only available on systems with GNU libc
...
-------------------------->8----------------------

Important disadvantages of a simple atexit() are that [2]:
-------------------------->8----------------------
1999 C Standard only requires that the implementation support 32 registered functions, although most implementations support many more.

Quoted 7 lines

More important it does not deal at all with the ability in most implementations to remove DSOs from a running program image by calling dlclose prior to program termination. -------------------------->8----------------------

Essentially for initial GCC there's no point in enabling that feature as we're not going to build CPP applications wit hit.

                                               ^^^^^^^ with it

But also, there's no point disabling the feature. So I'd set it to enabled in
both initial and final.

Quoted 3 lines

Also it seems like all libc's we support in Buildroot (Glibc, uClibc and musl) support __cxa_at_exit() so enable it unconditionally.

Also, it seems that gcc's configure will default it to yes and do a
AC_CHECK_FUNC(__cxa_atexit, ...) as well.

Finally, it looks like the handling of this option hasn't changed at all since
4.8, so we're safe in that aspect as well.

So, with the --enable in the common options:

Reviewed-by Arnout Vandecappelle (Essensium/Mind) <[email protected]>

Regards,
Arnout

Quoted 44 lines

[1] https://gcc.gnu.org/install/configure.html
[2] https://itanium-cxx-abi.github.io/cxx-abi/abi.html#dso-dtor-motivation

Signed-off-by Alexey Brodkin <[email protected]>
Cc Thomas Petazzoni <[email protected]>
Cc Mark Corbin <[email protected]>
Cc Romain Naour <[email protected]>
Cc Peter Korsgaard <[email protected]>
Cc Bernd Kuhls <[email protected]>
Cc Claudiu Zissulescu <[email protected]>
Cc Cupertino Miranda <[email protected]>
Cc Vineet Gupta <[email protected]>
---
 package/gcc/gcc-initial/gcc-initial.mk | 1 +
 package/gcc/gcc.mk                     | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
package/gcc/gcc-initial/gcc-initial.mk +1 -0
index d5d925a3d9..745a85607a 100644
@@ -40,6 +40,7 @@ HOST_GCC_INITIAL_CONF_OPTS = \
 	--with-newlib \
 	--disable-largefile \
 	--disable-nls \
+	--disable-__cxa_atexit \
 	$(call qstrip,$(BR2_EXTRA_GCC_CONFIG_OPTIONS))
 
 HOST_GCC_INITIAL_CONF_ENV = \
package/gcc/gcc.mk +1 -1
index e47435677e..5901624ea5 100644
@@ -87,7 +87,7 @@ HOST_GCC_COMMON_DEPENDENCIES = \
 HOST_GCC_COMMON_CONF_OPTS = \
 	--target=$(GNU_TARGET_NAME) \
 	--with-sysroot=$(STAGING_DIR) \
-	--disable-__cxa_atexit \
+	--enable-__cxa_atexit \
 	--with-gnu-ld \
 	--disable-libssp \
 	--disable-multilib \