[PATCH v2] libstdc++: Make certain exceptions transaction_safe.

[Jonathan Wakely]

On 16/01/16 14:35 +0100, Jakub Jelinek wrote:
>On Sat, Jan 16, 2016 at 07:47:33AM -0500, David Edelsohn wrote:
>> stage1 libstdc++ builds just fine.  the problem is stage2 configure
>> fails due to missing ITM_xxx symbols when configure tries to compile
>> and run conftest programs.
>
>On x86_64-linux, the _ITM_xxx symbols are undef weak ones and thus it is
>fine to load libstdc++ without libitm and libstdc++ doesn't depend on
>libitm.
>
>So, is AIX defining __GXX_WEAK__ or not?  Perhaps some other macro or
>configure check needs to be used to determine if undefined weak symbols
>work the way libstdc++ needs them to.
>
>#if __GXX_WEAK__
>// Declare all libitm symbols we rely on, but make them weak so that we do
>// not depend on libitm.
>extern void* _ZGTtnaX (size_t sz) __attribute__((weak));
>extern void _ZGTtdlPv (void* ptr) __attribute__((weak));
>extern uint8_t _ITM_RU1(const uint8_t *p)
>  ITM_REGPARM __attribute__((weak));
>extern uint32_t _ITM_RU4(const uint32_t *p)
>  ITM_REGPARM __attribute__((weak));
>extern uint64_t _ITM_RU8(const uint64_t *p)
>  ITM_REGPARM __attribute__((weak));
>extern void _ITM_memcpyRtWn(void *, const void *, size_t)
>  ITM_REGPARM __attribute__((weak));
>extern void _ITM_memcpyRnWt(void *, const void *, size_t)
>  ITM_REGPARM __attribute__((weak));
>extern void _ITM_addUserCommitAction(void (*)(void *), uint64_t, void *)
>  ITM_REGPARM __attribute__((weak));
>
>#else
>// If there is no support for weak symbols, create dummies.  The exceptions
>// will not be declared transaction_safe in this case.
>void* _ZGTtnaX (size_t) { return NULL; }
>void _ZGTtdlPv (void*) { }
>uint8_t _ITM_RU1(const uint8_t *) { return 0; }
>uint32_t _ITM_RU4(const uint32_t *) { return 0; }
>uint64_t _ITM_RU8(const uint64_t *) { return 0; }
>void _ITM_memcpyRtWn(void *, const void *, size_t) { }
>void _ITM_memcpyRnWt(void *, const void *, size_t) { }
>void _ITM_addUserCommitAction(void (*)(void *), uint64_t, void *) { };
>#endif

I think it's better to just drop that whole section of the file if TM
isn't supported, as this patch does.

Bootstraps OK on AIX, still testing on GNU/Linux.


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