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Subject[PATCH] proc: save LOC in vsyscall test
From: Brian Foster <bfoster@redhat.com>

Do one fork in vsyscall detection code and let SIGSEGV handler exit and
carry information to the parent saving LOC.

[
redo original patch,
delete unnecessary variables,
minimise code changes.
--adobriyan
]

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

tools/testing/selftests/proc/proc-pid-vm.c | 56 ++++++++---------------------
1 file changed, 16 insertions(+), 40 deletions(-)

--- a/tools/testing/selftests/proc/proc-pid-vm.c
+++ b/tools/testing/selftests/proc/proc-pid-vm.c
@@ -213,22 +213,22 @@ static int make_exe(const uint8_t *payload, size_t len)

/*
* 0: vsyscall VMA doesn't exist vsyscall=none
- * 1: vsyscall VMA is r-xp vsyscall=emulate
- * 2: vsyscall VMA is --xp vsyscall=xonly
+ * 1: vsyscall VMA is --xp vsyscall=xonly
+ * 2: vsyscall VMA is r-xp vsyscall=emulate
*/
-static int g_vsyscall;
+static volatile int g_vsyscall;
static const char *str_vsyscall;

static const char str_vsyscall_0[] = "";
static const char str_vsyscall_1[] =
-"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]\n";
-static const char str_vsyscall_2[] =
"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]\n";
+static const char str_vsyscall_2[] =
+"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]\n";

#ifdef __x86_64__
static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
{
- _exit(1);
+ _exit(g_vsyscall);
}

/*
@@ -255,6 +255,7 @@ static void vsyscall(void)
act.sa_sigaction = sigaction_SIGSEGV;
(void)sigaction(SIGSEGV, &act, NULL);

+ g_vsyscall = 0;
/* gettimeofday(NULL, NULL); */
asm volatile (
"call %P0"
@@ -262,45 +263,20 @@ static void vsyscall(void)
: "i" (0xffffffffff600000), "D" (NULL), "S" (NULL)
: "rax", "rcx", "r11"
);
- exit(0);
- }
- waitpid(pid, &wstatus, 0);
- if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0) {
- /* vsyscall page exists and is executable. */
- } else {
- /* vsyscall page doesn't exist. */
- g_vsyscall = 0;
- return;
- }
-
- pid = fork();
- if (pid < 0) {
- fprintf(stderr, "fork, errno %d\n", errno);
- exit(1);
- }
- if (pid == 0) {
- struct rlimit rlim = {0, 0};
- (void)setrlimit(RLIMIT_CORE, &rlim);
-
- /* Hide "segfault at ffffffffff600000" messages. */
- struct sigaction act;
- memset(&act, 0, sizeof(struct sigaction));
- act.sa_flags = SA_SIGINFO;
- act.sa_sigaction = sigaction_SIGSEGV;
- (void)sigaction(SIGSEGV, &act, NULL);

+ g_vsyscall = 1;
*(volatile int *)0xffffffffff600000UL;
- exit(0);
+
+ g_vsyscall = 2;
+ exit(g_vsyscall);
}
waitpid(pid, &wstatus, 0);
- if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0) {
- /* vsyscall page is readable and executable. */
- g_vsyscall = 1;
- return;
+ if (WIFEXITED(wstatus)) {
+ g_vsyscall = WEXITSTATUS(wstatus);
+ } else {
+ fprintf(stderr, "error: wstatus %08x\n", wstatus);
+ exit(1);
}
-
- /* vsyscall page is executable but unreadable. */
- g_vsyscall = 2;
}

int main(void)
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