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configure: Check for membarrier support #1704

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configure: Check for membarrier support #1704

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1 change: 1 addition & 0 deletions check-deps/Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ CHECK_LIST += have_libdw
CHECK_LIST += have_libunwind
CHECK_LIST += have_libcapstone
CHECK_LIST += cc_has_minline_all_stringops
CHECK_LIST += have_membarrier

#
# This is needed for checking build dependency
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4 changes: 4 additions & 0 deletions check-deps/Makefile.check
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Expand Up @@ -82,3 +82,7 @@ endif
ifneq ($(wildcard $(objdir)/check-deps/cc_has_minline_all_stringops),)
LIB_CFLAGS += -minline-all-stringops
endif

ifneq ($(wildcard $(objdir)/check-deps/have_membarrier),)
LIB_CFLAGS += -DHAVE_MEMBARRIER
endif
10 changes: 10 additions & 0 deletions check-deps/__have_membarrier.c
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@@ -0,0 +1,10 @@
#include <linux/membarrier.h>
#include <sys/syscall.h>
#include <unistd.h>

int main()
{
syscall(__NR_membarrier, MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE, 0, 0);
syscall(__NR_membarrier, MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE, 0, 0);
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By using _PRIVATE_EXPEDITED_SYNC_CORE, can we delete the old copy right after the syscall?

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Sorry, what do you mean by "the old copy"?

Here is an extract from the membarrier manual, for future reference:

MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE (since Linux 4.16)

In addition to providing the memory ordering guarantees described in MEMBARRIER_CMD_PRIVATE_EXPEDITED, upon return from system call the calling thread has a guarantee that all its running thread siblings have executed a core serializing instruction. This guarantee is provided only for threads in the same process as the calling thread.

The "expedited" commands complete faster than the non-expedited ones, they never block, but have the downside of causing extra overhead.

A process must register its intent to use the private expedited sync core command prior to using it.

MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE (since Linux 4.16)

Register the process's intent to use MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE.

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Sorry for the late reply. I think you want to use membarrier to update global state like in a RCU fashion. Something like below:

new_data = copy_data(shared_data);
add_some_data(new_data);

old_data = shared_data;
shared_data = new_data;  // WRITE_ONCE ?

membarrier();

free(old_data);

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That is somewhat true. We want to use membarriers to stop all running threads before entering patching/unpatching code as will be done in this other commit:
f07ab57

Note that this particular PR merely checks for availability of membarrier system call. The actual usage is left for PR #1747

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I know, I was just curious how it's gonna be used.

return 0;
}
3 changes: 3 additions & 0 deletions configure
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Expand Up @@ -35,6 +35,7 @@ usage() {
--without-capstone build without libcapstone (even if found on the system)
--without-perf build without perf event (even if available)
--without-schedule build without scheduler event (even if available)
--without-membarrier build without membarriers (even if available)

--arch=<ARCH> set target architecture (default: system default arch)
e.g. x86_64, aarch64, i386, or arm
Expand Down Expand Up @@ -198,6 +199,7 @@ for dep in $IGNORE; do
capstone) TARGET=have_libcapstone ;;
perf*) TARGET=perf_clockid ;;
sched*) TARGET=perf_context_switch;;
membarrier) TARGET=have_membarrier ;;
*) ;;
esac
if [ ! -z "$TARGET" ]; then
Expand Down Expand Up @@ -265,6 +267,7 @@ print_feature "perf_event" "perf_clockid" "perf (PMU) event support"
print_feature "schedule" "perf_context_switch" "scheduler event support"
print_feature "capstone" "have_libcapstone" "full dynamic tracing support"
print_feature "libunwind" "have_libunwind" "stacktrace support (optional for debugging)"
print_feature "membarrier" "have_membarrier" "membarrier support (requires Linux 4.16)"

cat >$output <<EOF
# this file is generated automatically
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