unittests: Adds step to remove stale SHM regions.

Some of the unit tests we run will leak shm regions. Presumably this is
because they never called `shmctl(IPC_RMID)` so the ID is laked forever.

This can be seen by querying `/proc/sysvipc/shm` to see a list of old
shm regions that eventually hit the maximum capacity of 4096 shm ids.

Once CI is done running, run a utility application that all it does is
check for SHM IDs that have zero attachments (thus unused), it was
created by the UID of the runner, and it is older than ten minutes. At
which point it will erase it.

This will fix spurious failures in our CI caused by running out of SHM
IDs, previously I had a cron job setup to restart the CI runners every
hour or so which caused its own spurious failure problems.

FINALLY this bug was triaged which has been annoying us for...years?

.github/workflows/ccpp.yml

@@ -241,6 +241,12 @@ jobs:
       # ASM tests get quite close to 10MB
       run: truncate --size=<20M ${{runner.workspace}}/build/Testing/Temporary/LastTest_*.log || true
 
+    - name: Remove old SHM regions
+      if: ${{ always() }}
+      shell: bash
+      working-directory: ${{runner.workspace}}/build
+      run: cmake --build . --config $BUILD_TYPE --target remove_old_shm_regions
+
     - name: Set runner name
       if: ${{ always() }}
       run: echo "runner_name=$(hostname)" >> $GITHUB_ENV

.github/workflows/glibc_fault.yml

@@ -176,6 +176,12 @@ jobs:
       # ASM tests get quite close to 10MB
       run: truncate --size=<20M ${{runner.workspace}}/build/Testing/Temporary/LastTest_*.log || true
 
+    - name: Remove old SHM regions
+      if: ${{ always() }}
+      shell: bash
+      working-directory: ${{runner.workspace}}/build
+      run: cmake --build . --config $BUILD_TYPE --target remove_old_shm_regions
+
     - name: Set runner name
       if: ${{ always() }}
       run: echo "runner_name=$(hostname)" >> $GITHUB_ENV

unittests/CMakeLists.txt

@@ -6,6 +6,7 @@ add_subdirectory(POSIX/)
 add_subdirectory(gvisor-tests/)
 add_subdirectory(gcc-target-tests-32/)
 add_subdirectory(gcc-target-tests-64/)
+add_subdirectory(Utilities/)
 
 if (BUILD_THUNKS)
   add_subdirectory(ThunkLibs)

unittests/Utilities/CMakeLists.txt

@@ -0,0 +1,10 @@
+add_executable(DeleteOldSHMRegions
+  DeleteOldSHMRegions.cpp)
+
+set_target_properties(DeleteOldSHMRegions PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/TestUtilities")
+add_custom_target(
+  remove_old_shm_regions
+  WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/TestUtilities/"
+  USES_TERMINAL
+  COMMAND "DeleteOldSHMRegions")
+

unittests/Utilities/DeleteOldSHMRegions.cpp

@@ -0,0 +1,42 @@
+#include <fstream>
+#include <stdio.h>
+#include <sys/shm.h>
+#include <unistd.h>
+
+static bool ctime_is_old(uint64_t ctime) {
+  time_t curtime;
+  time(&curtime);
+
+  // If it is older than ten minutes.
+  return (curtime - ctime) > 600;
+}
+
+int main() {
+  // key      shmid perms                  size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime                   rss                  swap
+  //	 0     360448   777                  4096 165187 165187      0  1002  1002  1002  1002 1679659857 1679659857 1679659857                  4096                     0
+  //	 0      32769   777                  4096 153814 153814      0  1002  1002  1002  1002 1676490841 1676490841 1676490841                     0                  4096
+  std::ifstream fs{"/proc/sysvipc/shm", std::fstream::binary};
+  std::string Line;
+
+  // Remove first line
+  std::getline(fs, Line);
+
+  const auto current_uid = getuid();
+  while (std::getline(fs, Line)) {
+    if (fs.eof()) break;
+    int shmid;
+    int uid;
+    int attach;
+    uint64_t ctime;
+    if (sscanf(Line.c_str(), "%*d %d %*d %*d %*d %*d %d %d %*d %*d %*d %*d %*d %ld", &shmid, &attach, &uid, &ctime) == 4) {
+      // If the UID matches and nothing is attached AND it is old then delete it.
+      if (uid == current_uid &&
+          attach == 0 &&
+          ctime_is_old(ctime)) {
+        shmctl(shmid, IPC_RMID, nullptr);
+      }
+    }
+  }
+  return 0;
+
+}