On Apr 5, 2016, at 2:20 PM, Jonathan Wakely <jwak...@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.
