* [GCC 12] libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880]
@ 2022-07-21 7:16 Sebastian Huber
2022-07-21 7:48 ` Jonathan Wakely
0 siblings, 1 reply; 3+ messages in thread
From: Sebastian Huber @ 2022-07-21 7:16 UTC (permalink / raw)
To: libstdc++; +Cc: Jonathan Wakely
From: Jonathan Wakely <jwakely@redhat.com>
This ensures that the single-threaded fallback buffer eh_globals is not
destroyed during program termination, using the same immortalization
technique used for error category objects.
Also ensure that init._M_init can still be read after init has been
destroyed, by making it a static data member.
libstdc++-v3/ChangeLog:
PR libstdc++/105880
* libsupc++/eh_globals.cc (eh_globals): Ensure constant init and
prevent destruction during termination.
(__eh_globals_init::_M_init): Replace with static member _S_init.
(__cxxabiv1::__cxa_get_globals_fast): Update.
(__cxxabiv1::__cxa_get_globals): Likewise.
(cherry picked from commit 1e65f2ed99024f23c56f7b6a961898bcaa882a92)
---
Would it be acceptable to back port this fix to GCC 12?
libstdc++-v3/libsupc++/eh_globals.cc | 51 ++++++++++++++++++++--------
1 file changed, 37 insertions(+), 14 deletions(-)
diff --git a/libstdc++-v3/libsupc++/eh_globals.cc b/libstdc++-v3/libsupc++/eh_globals.cc
index 3a003b89edf..768425c0f40 100644
--- a/libstdc++-v3/libsupc++/eh_globals.cc
+++ b/libstdc++-v3/libsupc++/eh_globals.cc
@@ -64,8 +64,26 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
#else
-// Single-threaded fallback buffer.
-static __cxa_eh_globals eh_globals;
+#if __has_cpp_attribute(clang::require_constant_initialization)
+# define __constinit [[clang::require_constant_initialization]]
+#endif
+
+namespace
+{
+ struct constant_init
+ {
+ union {
+ unsigned char unused;
+ __cxa_eh_globals obj;
+ };
+ constexpr constant_init() : obj() { }
+
+ ~constant_init() { /* do nothing, union member is not destroyed */ }
+ };
+
+ // Single-threaded fallback buffer.
+ __constinit constant_init eh_globals;
+}
#if __GTHREADS
@@ -90,32 +108,37 @@ eh_globals_dtor(void* ptr)
struct __eh_globals_init
{
__gthread_key_t _M_key;
- bool _M_init;
+ static bool _S_init;
- __eh_globals_init() : _M_init(false)
- {
+ __eh_globals_init()
+ {
if (__gthread_active_p())
- _M_init = __gthread_key_create(&_M_key, eh_globals_dtor) == 0;
+ _S_init = __gthread_key_create(&_M_key, eh_globals_dtor) == 0;
}
~__eh_globals_init()
{
- if (_M_init)
+ if (_S_init)
__gthread_key_delete(_M_key);
- _M_init = false;
+ _S_init = false;
}
+
+ __eh_globals_init(const __eh_globals_init&) = delete;
+ __eh_globals_init& operator=(const __eh_globals_init&) = delete;
};
+bool __eh_globals_init::_S_init = false;
+
static __eh_globals_init init;
extern "C" __cxa_eh_globals*
__cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
{
__cxa_eh_globals* g;
- if (init._M_init)
+ if (init._S_init)
g = static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key));
else
- g = &eh_globals;
+ g = &eh_globals.obj;
return g;
}
@@ -123,7 +146,7 @@ extern "C" __cxa_eh_globals*
__cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
{
__cxa_eh_globals* g;
- if (init._M_init)
+ if (init._S_init)
{
g = static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key));
if (!g)
@@ -140,7 +163,7 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
}
}
else
- g = &eh_globals;
+ g = &eh_globals.obj;
return g;
}
@@ -148,11 +171,11 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
extern "C" __cxa_eh_globals*
__cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
-{ return &eh_globals; }
+{ return &eh_globals.obj; }
extern "C" __cxa_eh_globals*
__cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
-{ return &eh_globals; }
+{ return &eh_globals.obj; }
#endif
--
2.35.3
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [GCC 12] libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880]
2022-07-21 7:16 [GCC 12] libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880] Sebastian Huber
@ 2022-07-21 7:48 ` Jonathan Wakely
2022-10-12 10:55 ` Jonathan Wakely
0 siblings, 1 reply; 3+ messages in thread
From: Jonathan Wakely @ 2022-07-21 7:48 UTC (permalink / raw)
To: Sebastian Huber; +Cc: libstdc++, Jonathan Wakely
On Thu, 21 Jul 2022, 08:16 Sebastian Huber, <
sebastian.huber@embedded-brains.de> wrote:
> From: Jonathan Wakely <jwakely@redhat.com>
>
> This ensures that the single-threaded fallback buffer eh_globals is not
> destroyed during program termination, using the same immortalization
> technique used for error category objects.
>
> Also ensure that init._M_init can still be read after init has been
> destroyed, by making it a static data member.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/105880
> * libsupc++/eh_globals.cc (eh_globals): Ensure constant init and
> prevent destruction during termination.
> (__eh_globals_init::_M_init): Replace with static member _S_init.
> (__cxxabiv1::__cxa_get_globals_fast): Update.
> (__cxxabiv1::__cxa_get_globals): Likewise.
>
> (cherry picked from commit 1e65f2ed99024f23c56f7b6a961898bcaa882a92)
> ---
>
> Would it be acceptable to back port this fix to GCC 12?
>
Yes, it's ok for gcc-12
> libstdc++-v3/libsupc++/eh_globals.cc | 51 ++++++++++++++++++++--------
> 1 file changed, 37 insertions(+), 14 deletions(-)
>
> diff --git a/libstdc++-v3/libsupc++/eh_globals.cc
> b/libstdc++-v3/libsupc++/eh_globals.cc
> index 3a003b89edf..768425c0f40 100644
> --- a/libstdc++-v3/libsupc++/eh_globals.cc
> +++ b/libstdc++-v3/libsupc++/eh_globals.cc
> @@ -64,8 +64,26 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>
> #else
>
> -// Single-threaded fallback buffer.
> -static __cxa_eh_globals eh_globals;
> +#if __has_cpp_attribute(clang::require_constant_initialization)
> +# define __constinit [[clang::require_constant_initialization]]
> +#endif
> +
> +namespace
> +{
> + struct constant_init
> + {
> + union {
> + unsigned char unused;
> + __cxa_eh_globals obj;
> + };
> + constexpr constant_init() : obj() { }
> +
> + ~constant_init() { /* do nothing, union member is not destroyed */ }
> + };
> +
> + // Single-threaded fallback buffer.
> + __constinit constant_init eh_globals;
> +}
>
> #if __GTHREADS
>
> @@ -90,32 +108,37 @@ eh_globals_dtor(void* ptr)
> struct __eh_globals_init
> {
> __gthread_key_t _M_key;
> - bool _M_init;
> + static bool _S_init;
>
> - __eh_globals_init() : _M_init(false)
> - {
> + __eh_globals_init()
> + {
> if (__gthread_active_p())
> - _M_init = __gthread_key_create(&_M_key, eh_globals_dtor) == 0;
> + _S_init = __gthread_key_create(&_M_key, eh_globals_dtor) == 0;
> }
>
> ~__eh_globals_init()
> {
> - if (_M_init)
> + if (_S_init)
> __gthread_key_delete(_M_key);
> - _M_init = false;
> + _S_init = false;
> }
> +
> + __eh_globals_init(const __eh_globals_init&) = delete;
> + __eh_globals_init& operator=(const __eh_globals_init&) = delete;
> };
>
> +bool __eh_globals_init::_S_init = false;
> +
> static __eh_globals_init init;
>
> extern "C" __cxa_eh_globals*
> __cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
> {
> __cxa_eh_globals* g;
> - if (init._M_init)
> + if (init._S_init)
> g =
> static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key));
> else
> - g = &eh_globals;
> + g = &eh_globals.obj;
> return g;
> }
>
> @@ -123,7 +146,7 @@ extern "C" __cxa_eh_globals*
> __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
> {
> __cxa_eh_globals* g;
> - if (init._M_init)
> + if (init._S_init)
> {
> g =
> static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key));
> if (!g)
> @@ -140,7 +163,7 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
> }
> }
> else
> - g = &eh_globals;
> + g = &eh_globals.obj;
> return g;
> }
>
> @@ -148,11 +171,11 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>
> extern "C" __cxa_eh_globals*
> __cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
> -{ return &eh_globals; }
> +{ return &eh_globals.obj; }
>
> extern "C" __cxa_eh_globals*
> __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
> -{ return &eh_globals; }
> +{ return &eh_globals.obj; }
>
> #endif
>
> --
> 2.35.3
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [GCC 12] libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880]
2022-07-21 7:48 ` Jonathan Wakely
@ 2022-10-12 10:55 ` Jonathan Wakely
0 siblings, 0 replies; 3+ messages in thread
From: Jonathan Wakely @ 2022-10-12 10:55 UTC (permalink / raw)
To: Jonathan Wakely; +Cc: Sebastian Huber, libstdc++
On Thu, 21 Jul 2022 at 08:48, Jonathan Wakely wrote:
>
>
>
> On Thu, 21 Jul 2022, 08:16 Sebastian Huber, <sebastian.huber@embedded-brains.de> wrote:
>>
>> From: Jonathan Wakely <jwakely@redhat.com>
>>
>> This ensures that the single-threaded fallback buffer eh_globals is not
>> destroyed during program termination, using the same immortalization
>> technique used for error category objects.
>>
>> Also ensure that init._M_init can still be read after init has been
>> destroyed, by making it a static data member.
>>
>> libstdc++-v3/ChangeLog:
>>
>> PR libstdc++/105880
>> * libsupc++/eh_globals.cc (eh_globals): Ensure constant init and
>> prevent destruction during termination.
>> (__eh_globals_init::_M_init): Replace with static member _S_init.
>> (__cxxabiv1::__cxa_get_globals_fast): Update.
>> (__cxxabiv1::__cxa_get_globals): Likewise.
>>
>> (cherry picked from commit 1e65f2ed99024f23c56f7b6a961898bcaa882a92)
>> ---
>>
>> Would it be acceptable to back port this fix to GCC 12?
>
>
> Yes, it's ok for gcc-12
But the a33dda016e5acf9c6325ce8a72a1b0238130374e follow-up is also
needed on the branch. I'll take care of that.
>
>
>
>>
>> libstdc++-v3/libsupc++/eh_globals.cc | 51 ++++++++++++++++++++--------
>> 1 file changed, 37 insertions(+), 14 deletions(-)
>>
>> diff --git a/libstdc++-v3/libsupc++/eh_globals.cc b/libstdc++-v3/libsupc++/eh_globals.cc
>> index 3a003b89edf..768425c0f40 100644
>> --- a/libstdc++-v3/libsupc++/eh_globals.cc
>> +++ b/libstdc++-v3/libsupc++/eh_globals.cc
>> @@ -64,8 +64,26 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>>
>> #else
>>
>> -// Single-threaded fallback buffer.
>> -static __cxa_eh_globals eh_globals;
>> +#if __has_cpp_attribute(clang::require_constant_initialization)
>> +# define __constinit [[clang::require_constant_initialization]]
>> +#endif
>> +
>> +namespace
>> +{
>> + struct constant_init
>> + {
>> + union {
>> + unsigned char unused;
>> + __cxa_eh_globals obj;
>> + };
>> + constexpr constant_init() : obj() { }
>> +
>> + ~constant_init() { /* do nothing, union member is not destroyed */ }
>> + };
>> +
>> + // Single-threaded fallback buffer.
>> + __constinit constant_init eh_globals;
>> +}
>>
>> #if __GTHREADS
>>
>> @@ -90,32 +108,37 @@ eh_globals_dtor(void* ptr)
>> struct __eh_globals_init
>> {
>> __gthread_key_t _M_key;
>> - bool _M_init;
>> + static bool _S_init;
>>
>> - __eh_globals_init() : _M_init(false)
>> - {
>> + __eh_globals_init()
>> + {
>> if (__gthread_active_p())
>> - _M_init = __gthread_key_create(&_M_key, eh_globals_dtor) == 0;
>> + _S_init = __gthread_key_create(&_M_key, eh_globals_dtor) == 0;
>> }
>>
>> ~__eh_globals_init()
>> {
>> - if (_M_init)
>> + if (_S_init)
>> __gthread_key_delete(_M_key);
>> - _M_init = false;
>> + _S_init = false;
>> }
>> +
>> + __eh_globals_init(const __eh_globals_init&) = delete;
>> + __eh_globals_init& operator=(const __eh_globals_init&) = delete;
>> };
>>
>> +bool __eh_globals_init::_S_init = false;
>> +
>> static __eh_globals_init init;
>>
>> extern "C" __cxa_eh_globals*
>> __cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
>> {
>> __cxa_eh_globals* g;
>> - if (init._M_init)
>> + if (init._S_init)
>> g = static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key));
>> else
>> - g = &eh_globals;
>> + g = &eh_globals.obj;
>> return g;
>> }
>>
>> @@ -123,7 +146,7 @@ extern "C" __cxa_eh_globals*
>> __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>> {
>> __cxa_eh_globals* g;
>> - if (init._M_init)
>> + if (init._S_init)
>> {
>> g = static_cast<__cxa_eh_globals*>(__gthread_getspecific(init._M_key));
>> if (!g)
>> @@ -140,7 +163,7 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>> }
>> }
>> else
>> - g = &eh_globals;
>> + g = &eh_globals.obj;
>> return g;
>> }
>>
>> @@ -148,11 +171,11 @@ __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>>
>> extern "C" __cxa_eh_globals*
>> __cxxabiv1::__cxa_get_globals_fast() _GLIBCXX_NOTHROW
>> -{ return &eh_globals; }
>> +{ return &eh_globals.obj; }
>>
>> extern "C" __cxa_eh_globals*
>> __cxxabiv1::__cxa_get_globals() _GLIBCXX_NOTHROW
>> -{ return &eh_globals; }
>> +{ return &eh_globals.obj; }
>>
>> #endif
>>
>> --
>> 2.35.3
>>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-07-21 7:16 [GCC 12] libstdc++: Fix lifetime bugs for non-TLS eh_globals [PR105880] Sebastian Huber
2022-07-21 7:48 ` Jonathan Wakely
2022-10-12 10:55 ` Jonathan Wakely
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