proc: support proc-empty-vm test on i386

Unmap everything starting from 4GB length until it unmaps, otherwise test
has to detect which virtual memory split kernel is using.

Link: https://lkml.kernel.org/r/20230630183434.17434-1-adobriyan@gmail.comSigned-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Björn Töpel <bjorn@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/proc/proc-empty-vm.c

@@ -37,6 +37,10 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+#ifdef __amd64__
+#define TEST_VSYSCALL
+#endif
+
 /*
  * 0: vsyscall VMA doesn't exist	vsyscall=none
  * 1: vsyscall VMA is --xp		vsyscall=xonly
@@ -119,6 +123,7 @@ static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
 	_exit(EXIT_FAILURE);
 }
 
+#ifdef TEST_VSYSCALL
 static void sigaction_SIGSEGV_vsyscall(int _, siginfo_t *__, void *___)
 {
 	_exit(g_vsyscall);
@@ -170,6 +175,7 @@ static void vsyscall(void)
 		exit(1);
 	}
 }
+#endif
 
 static int test_proc_pid_maps(pid_t pid)
 {
@@ -299,7 +305,9 @@ int main(void)
 {
 	int rv = EXIT_SUCCESS;
 
+#ifdef TEST_VSYSCALL
 	vsyscall();
+#endif
 
 	switch (g_vsyscall) {
 	case 0:
@@ -346,6 +354,14 @@ int main(void)
 
 #ifdef __amd64__
 		munmap(NULL, ((size_t)1 << 47) - 4096);
+#elif defined __i386__
+		{
+			size_t len;
+
+			for (len = -4096;; len -= 4096) {
+				munmap(NULL, len);
+			}
+		}
 #else
 #error "implement 'unmap everything'"
 #endif