Re: [PATCH] Check for POSIX_MADV_WILLNEED to support building against the LSB

[Michael Hope <michael.hope@linaro.org>]

On 11 June 2012 17:59, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> Date: Mon, 11 Jun 2012 16:25:22 +1200
>> From: Michael Hope <michael.hope@linaro.org>
>>
>> The Linux Standard Base APIs include posix_madvise() but don't define
>> values for the 'advice' argument.  Check to see if POSIX_MADV_WILLNEED
>> is defined before using.
>
> What real-world problem does this fix?

Being able to build GDB using the LSB tools so that you can make a
binary release that works on any Linux distro from RHEL4 and above.
We use it for the linaro-toolchain-binaries.

> It makes no sense to have
> posix_madvise() but not define any values for the 'advice' argument.
> I'd say this is a "bug" in LSB.  Either they should drop
> posix_madvise() from the standard, or include at least the 'advice'
> values required by POSIX.

The LSB has a policy of not dropping functions.  I can suggest that
they add the advise values for a later version but that will take some
time and won't cover existing LSB releases.

I could change this to a configure test similar to HAS_MADVISE but
it's bad practice to separate the check from the use.

-- Michael

>> 2012-06-11  Michael Hope  <michael.hope@linaro.org>
>>
>>       * dwarf2read.c (dwarf2_read_section): Check for
>>       POSIX_MADV_WILLNEED.
>>
>> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
>> index 589361e..91fab5a 100644
>> --- a/gdb/dwarf2read.c
>> +++ b/gdb/dwarf2read.c
>> @@ -1773,7 +1773,7 @@ dwarf2_read_section (struct objfile *objfile, struct dwarf2_section_info *info)
>>
>>         if ((caddr_t)info->buffer != MAP_FAILED)
>>          {
>> -#if HAVE_POSIX_MADVISE
>> +#if HAVE_POSIX_MADVISE && defined(POSIX_MADV_WILLNEED)
>>            posix_madvise (info->map_addr, info->map_len, POSIX_MADV_WILLNEED);
>>   #endif
>>            return;
>>