[PATCH] elf: Support at least 32-byte alignment in static dlopen
Vineet Gupta
Vineet.Gupta1@synopsys.com
Fri Jul 10 21:19:55 GMT 2020
On 7/10/20 1:49 PM, Carlos O'Donell via Libc-alpha wrote:
> On 7/10/20 4:26 PM, Florian Weimer via Libc-alpha wrote:
>> Otherwise loading a dynamically linked libc with rseq support fails,
>> as result of the __rseq_abi TLS variable, which has an alignment
>> of 32 bytes.
>
> OK for 2.32.
>
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Fixes most of the ARC issues.
Tested-by: Vineet Gupta <vgupta@synopsys.com>
>> ---
>> csu/libc-tls.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/csu/libc-tls.c b/csu/libc-tls.c
>> index 06e76bd395..3f1655f264 100644
>> --- a/csu/libc-tls.c
>> +++ b/csu/libc-tls.c
>> @@ -112,6 +112,12 @@ __libc_setup_tls (void)
>> size_t tcb_offset;
>> const ElfW(Phdr) *phdr;
>>
>> + /* libc.so with rseq has TLS with 32-byte alignment. Static dlopen
>> + requires at least 32-byte alignment as well, otherwise loading
>> + libc.so will always fail. */
>> + if (max_align < 32)
>> + max_align = 32;
>
> OK. Same problem as the previous discuss, namely that you'd need to look
> over all the modules you're going to dlopen first to compute a value
> that is large enough. All we're doing here is papering over a design problem,
> but that is OK for 2.32. Eventually we're going to need to do some kind of
> redesign here to make this more reliable.
>
>> +
>> struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
>>
>> /* Look through the TLS segment if there is any. */
>>
>
>
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