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Re: [RFC] fix bootstrap on aarch64-*-freebsd and probably others
On 19/01/17 06:38, Andreas Tobler wrote:
> On 19.01.17 00:33, Jeff Law wrote:
>> On 01/18/2017 11:43 AM, Andreas Tobler wrote:
>>> Hi all,
>>>
>>> I have the following issue here on aarch64-*-freebsd:
>>>
>>> (sorry if the format is hardly readable)
>>>
>>> ......
>>> /export/devel/net/src/gcc/head/gcc/gcc/config/aarch64/aarch64.c: In
>>> function 'void aarch64_elf_asm_destructor(rtx, int)':
>>> /export/devel/net/src/gcc/head/gcc/gcc/config/aarch64/aarch64.c:5760:1:
>>> error: %.5u' directive output may be truncated writing between 5 and 10
>>> bytes into a region of size 6 [-Werror=format-truncation=]
>>> aarch64_elf_asm_destructor (rtx symbol, int priority)
>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~
>>> /export/devel/net/src/gcc/head/gcc/gcc/config/aarch64/aarch64.c:5760:1:
>>> note: using the range [1, 4294967295] for directive argument
>>> /export/devel/net/src/gcc/head/gcc/gcc/config/aarch64/aarch64.c:5768:65:
>>> note: format output between 18 and 23 bytes into a destination of
>>> size 18
>>> snprintf (buf, sizeof (buf), ".fini_array.%.5u", priority);
>>>
>>> ^
>>> .......
>>>
>>> This is the code snippet, it does not only occur in aarch64, but also at
>>> least in pa and avr.
>>>
>>> ----
>>> static void
>>> aarch64_elf_asm_destructor (rtx symbol, unsigned short priority)
>>> {
>>> if (priority == DEFAULT_INIT_PRIORITY)
>>> default_dtor_section_asm_out_destructor (symbol, priority);
>>> else
>>> {
>>> section *s;
>>> char buf[18];
>>> snprintf (buf, sizeof (buf), ".fini_array.%.5u", priority);
>>> s = get_section (buf, SECTION_WRITE, NULL);
>>> switch_to_section (s);
>>> assemble_align (POINTER_SIZE);
>>> assemble_aligned_integer (POINTER_BYTES, symbol);
>>> }
>>> }
>>> ----
>>>
>>> I have now four options to solve this, (a fifth one would be to remove
>>> format-truncation from -Wall/Wextra?)
>>>
>>> 1.) increase buf to 23
>>> 2.) use %.5hu in snprintf
>>> 3.) cast priority in snprintf to (unsigned int)
>>> 4.) make priority unsigned short.
>>>
>>> Solution 1, 2 and 3 work, but with pros and cons.
>> #3 likely won't work with with lower optimization levels since it
>> depends on VRP to narrow the object's range.
>>
>> I'd approve #2 or #1 without hesitation.
>
> Ok.
>
> I did a mistake while describing the situation. The function has this
> parameter:
>
> aarch64_elf_asm_destructor (rtx symbol, int priority)
>
> I copied the already modified piece of code....
>
Ah, that makes much more sense.
> So the cast in #3 would be (unsigned short) iso (unsigned int).
>
> If no other opinions come up I'll go with #2.
>
> Thanks.
> Andreas
>
>
I agree, some sort of cast seems preferable. The documentation for
constructor priorities says that the lowest priority is 65535, so
alternatives here are:
- assert (priority < 65536) then cast to unsigned short.
- simply cast to unsigned short
- saturate to 16 bits unsigned then cast to short.
Which is best will depend on what the front/mid ends might have done to
apply the documented limit.
R.