Re: [PATCH v3 06/16] asprintf_chk: Ensure compatibility for both s390x and ppc64le

[Rajalakshmi Srinivasaraghavan <rajis@linux.vnet.ibm.com>]

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On 6/30/23 10:11 AM, Siddhesh Poyarekar wrote:
> Subject:
> Re: [PATCH v3 06/16] asprintf_chk: Ensure compatibility for both s390x 
> and ppc64le
> From:
> Siddhesh Poyarekar <siddhesh@gotplt.org>
> Date:
> 6/30/23, 10:11 AM
>
> To:
> Frédéric Bérat <fberat@redhat.com>, libc-alpha@sourceware.org
> CC:
> Stefan Liebler <stli@linux.ibm.com>, Rajalakshmi Srinivasaraghavan 
> <rajis@linux.vnet.ibm.com>
>
>
>
>
> On 2023-06-28 04:42, Frédéric Bérat wrote:
>> If ldbl_* macros are used for asprintf, ABI gets broken on s390x,
>> if it isn't, ppc64le isn't building due to multiple asm redirections.
>>
>> This is due to the inclusion of bits/stdio-lbdl.h for ppc64le whereas it
>> isn't for s390x. This header creates redirections, which are not
>> compatible with the ones generated using libc_hidden_builtin_def.
>> Yet, we can't use libc_hidden_ldbl_proto on s390x since it will not
>> create a simple strong alias (e.g. as done on x86_64), but a versioned
>> alias, leading to ABI breakage.
>> ---
>
> Looks OK to me, but deferring to the IBM maintainers.  Raji, Stefan, 
> does this look right to you?


Paul Murphy is our expert on this topic.  Paul,  Can you comment on this 
too?  Thanks.

>
> Thanks,
> Sid
>
>
>> debug/asprintf_chk.c | 12 ++++++++++++
>>   include/stdio.h      |  5 +++++
>>   2 files changed, 17 insertions(+)
>>
>> diff --git a/debug/asprintf_chk.c b/debug/asprintf_chk.c
>> index 06d112de00..7da1cddacb 100644
>> --- a/debug/asprintf_chk.c
>> +++ b/debug/asprintf_chk.c
>> @@ -36,5 +36,17 @@ ___asprintf_chk (char **result_ptr, int flag, 
>> const char *format, ...)
>>       return ret;
>>   }
>> +#if defined __LDBL_COMPAT || __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
>> +/* This is needed since <bits/stdio-lbdl.h> is included in this 
>> case, leading to
>> + * multiple asm redirection of the same symbol
>> + */
>>   ldbl_hidden_def (___asprintf_chk, __asprintf_chk)
>>   ldbl_strong_alias (___asprintf_chk, __asprintf_chk)
>> +#else
>> +/* Yet, we can't use ldbl_* macros on some systems, even if they 
>> don't fall in
>> + * the first case as this leads to ABI breakage due to the 
>> long_double_symbol
>> + * aliasing, which is versionned.
>> + */
>> +strong_alias (___asprintf_chk, __asprintf_chk)
>> +libc_hidden_builtin_def (__asprintf_chk)
>> +#endif
>> diff --git a/include/stdio.h b/include/stdio.h
>> index 3afb0ff77b..6755877911 100644
>> --- a/include/stdio.h
>> +++ b/include/stdio.h
>> @@ -279,7 +279,12 @@ rtld_hidden_proto (__libc_fatal)
>>     libc_hidden_proto (__fgets_unlocked_chk)
>>   +#if defined __LDBL_COMPAT || __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
>>   libc_hidden_ldbl_proto (__asprintf_chk)
>> +#else
>> +libc_hidden_proto (__asprintf_chk)
>> +#endif
>> +
>>   libc_hidden_ldbl_proto (__fprintf_chk)
>>   libc_hidden_ldbl_proto (__sprintf_chk)
>>   libc_hidden_ldbl_proto (__vsprintf_chk)