Re: [PATCH v2 3/4] elf: Avoid RELATIVE relocs in __tunables_init

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 11/01/2021 07:56, Szabolcs Nagy wrote:
> The 01/08/2021 14:59, Adhemerval Zanella wrote:
>> On 08/01/2021 13:20, Szabolcs Nagy via Libc-alpha wrote:
>>> With static pie linking pointers in the tunables list need
>>> RELATIVE relocs since the absolute address is not known at link
>>> time. We want to avoid relocations so the static pie self
>>> relocation can be done after tunables are initialized.
>>>
>>> This is a quick fix that increases the tunable list size a bit.
> ...
>>> --- a/elf/dl-tunables.h
>>> +++ b/elf/dl-tunables.h
>>> @@ -38,7 +38,7 @@ __tunables_init (char **unused __attribute__ ((unused)))
>>>  /* A tunable.  */
>>>  struct _tunable
>>>  {
>>> -  const char *name;			/* Internal name of the tunable.  */
>>> +  const char name[64];			/* Internal name of the tunable.  */
>>>    tunable_type_t type;			/* Data type of the tunable.  */
>>>    tunable_val_t val;			/* The value.  */
>>>    bool initialized;			/* Flag to indicate that the tunable is
>>> @@ -54,7 +54,7 @@ struct _tunable
>>>  					   target module if the value is
>>>  					   considered unsafe.  */
>>>    /* Compatibility elements.  */
>>> -  const char *env_alias;		/* The compatibility environment
>>> +  const char env_alias[24];		/* The compatibility environment
>>>  					   variable name.  */
>>>  };
>>
>> The change is ok, although I think we can at least not make the maximum r
>> equired size being automatically generated at build time:
>>
> ...
>> --- a/elf/dl-tunables.h
>> +++ b/elf/dl-tunables.h
>> @@ -34,11 +34,12 @@ __tunables_init (char **unused __attribute__ ((unused)))
>>  
>>  # include <stddef.h>
>>  # include "dl-tunable-types.h"
>> +# include "dl-tunable-list-max.h"
>>  
>>  /* A tunable.  */
>>  struct _tunable
>>  {
>> -  const char *name;			/* Internal name of the tunable.  */
>> +  const char name[TUNABLES_NAME_MAX];	/* Internal name of the tunable.  */
>>    tunable_type_t type;			/* Data type of the tunable.  */
>>    tunable_val_t val;			/* The value.  */
>>    bool initialized;			/* Flag to indicate that the tunable is
>> @@ -54,7 +55,7 @@ struct _tunable
>>  					   target module if the value is
>>  					   considered unsafe.  */
>>    /* Compatibility elements.  */
>> -  const char *env_alias;		/* The compatibility environment
>> +  const char env_alias[TUNABLES_ALIAS_MAX];/* The compatibility environment
>>  					   variable name.  */
>>  };
> 
> yeah i can do this,
> it's also possible to collect all strings
> in one char array and iterate over them or
> keep offsets to them in struct _tunable
> instead of pointers.
> 

Yes, this is pretty much what stdio-common/errlist.c does for errno names.