Re: [PATCH] Fix detection of setrlimit in libstdc++ testsuite

[Jonathan Wakely <jwakely@redhat.com>]

On 31/08/16 14:22 +0300, Maxim Kuvyrkov wrote:
>> On Apr 5, 2016, at 2:20 PM, Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>>> This patch fixes an obscure cross-testing problem that crashed (OOMed) our boards at Linaro.  Several tests in libstdc++ (e.g., [1]) limit themselves to some reasonable amount of RAM and then try to allocate 32 gigs.  Unfortunately, the configure test that checks presence of setrlimit is rather strange: if target is native, then try compile file with call to setrlimit -- if compilation succeeds, then use setrlimit, otherwise, ignore setrlimit.  The strange part is that the compilation check is done only for native targets, as if cross-toolchains can't generate working executables.  [This is rather odd, and I might be missing some underlaying caveat.]
>>
>> I went spelunking, and the IS_NATIVE check has been there since
>> r70167, which replaced:
>>
>> if test  x"$GLIBCXX_IS_CROSS_COMPILING" = xfalse; then
>>   # Do checks for memory limit functions.
>>   GLIBCXX_CHECK_SETRLIMIT
>>
>> That arrived in r68067, but that seems to eb just a refactoring, and I
>> got lost tracking it further.
>>
>> So there has been a similar check since at least 2003.
>>
>>> Therefore, when testing a cross toolchain, the test [1] still tries to allocate 32GB of RAM with no setrlimit restrictions.  On most targets that people use for cross-testing this is not an issue because either
>>> - the target is 32-bit, so there is no 32GB user-space to speak of, or
>>> - the target board has small amount of RAM and no swap, so allocation immediately fails, or
>>> - the target board has plenty of RAM, so allocating 32GB is not an issue.
>>>
>>> However, if one is testing on a 64-bit board with 16GB or RAM and 16GB of swap, then one gets into an obscure near-OOM swapping condition.  This is exactly the case with cross-testing aarch64-linux-gnu toolchains on APM Mustang.
>>>
>>> The attached patch removes "native" restriction from configure test for setrlimit.  This enables setrlimit restrictions on the testsuite, and the test [1] expectedly fails to allocate 32GB due to setrlimit restriction.
>>>
>>> I have tested it on x86_64-linux-gnu and i686-linux-gnu native toolchains, and aarch64-linux-gnu and arm-linux-gnueabi[hf] cross-toolchains with no regressions [*].
>>>
>>> OK to commit?
>>
>> This issue has been present for well over a decade so it doesn't seem
>> critical to fix in stage4, but as it only affects the testsuite I am
>> OK with the change if the RMs have no objections.
>
>Hi Jonathan,
>
>This issue dropped off my patch queue.  The original patch still applies without conflicts, and I'm retesting it on fresh mainline -- both cross and native.
>
>OK to commit if no regressions?

Yes, OK. Thanks.