[PATCH v7 4/6] selftest/sigaltstack: Use the AT_MINSIGSTKSZ aux vector if available

[Chang S. Bae]

The SIGSTKSZ constant may not represent enough stack size in some
architectures as the hardware state size grows.

Use getauxval(AT_MINSIGSTKSZ) to increase the stack size.

Signed-off-by: Chang S. Bae <chang.seok....@intel.com>
Reviewed-by: Len Brown <len.br...@intel.com>
Cc: linux-kselft...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from v5:
* Added as a new patch.
---
 tools/testing/selftests/sigaltstack/sas.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/sigaltstack/sas.c 
b/tools/testing/selftests/sigaltstack/sas.c
index 8934a3766d20..c53b070755b6 100644
--- a/tools/testing/selftests/sigaltstack/sas.c
+++ b/tools/testing/selftests/sigaltstack/sas.c
@@ -17,6 +17,7 @@
 #include <string.h>
 #include <assert.h>
 #include <errno.h>
+#include <sys/auxv.h>
 
 #include "../kselftest.h"
 
@@ -24,6 +25,11 @@
 #define SS_AUTODISARM  (1U << 31)
 #endif
 
+#ifndef AT_MINSIGSTKSZ
+#define AT_MINSIGSTKSZ 51
+#endif
+
+static unsigned int stack_size;
 static void *sstack, *ustack;
 static ucontext_t uc, sc;
 static const char *msg = "[OK]\tStack preserved";
@@ -47,7 +53,7 @@ void my_usr1(int sig, siginfo_t *si, void *u)
 #endif
 
        if (sp < (unsigned long)sstack ||
-                       sp >= (unsigned long)sstack + SIGSTKSZ) {
+                       sp >= (unsigned long)sstack + stack_size) {
                ksft_exit_fail_msg("SP is not on sigaltstack\n");
        }
        /* put some data on stack. other sighandler will try to overwrite it */
@@ -108,6 +114,10 @@ int main(void)
        stack_t stk;
        int err;
 
+       /* Make sure more than the required minimum. */
+       stack_size = getauxval(AT_MINSIGSTKSZ) + SIGSTKSZ;
+       ksft_print_msg("[NOTE]\tthe stack size is %lu\n", stack_size);
+
        ksft_print_header();
        ksft_set_plan(3);
 
@@ -117,7 +127,7 @@ int main(void)
        sigaction(SIGUSR1, &act, NULL);
        act.sa_sigaction = my_usr2;
        sigaction(SIGUSR2, &act, NULL);
-       sstack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
+       sstack = mmap(NULL, stack_size, PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
        if (sstack == MAP_FAILED) {
                ksft_exit_fail_msg("mmap() - %s\n", strerror(errno));
@@ -139,7 +149,7 @@ int main(void)
        }
 
        stk.ss_sp = sstack;
-       stk.ss_size = SIGSTKSZ;
+       stk.ss_size = stack_size;
        stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
        err = sigaltstack(&stk, NULL);
        if (err) {
@@ -161,7 +171,7 @@ int main(void)
                }
        }
 
-       ustack = mmap(NULL, SIGSTKSZ, PROT_READ | PROT_WRITE,
+       ustack = mmap(NULL, stack_size, PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
        if (ustack == MAP_FAILED) {
                ksft_exit_fail_msg("mmap() - %s\n", strerror(errno));
@@ -170,7 +180,7 @@ int main(void)
        getcontext(&uc);
        uc.uc_link = NULL;
        uc.uc_stack.ss_sp = ustack;
-       uc.uc_stack.ss_size = SIGSTKSZ;
+       uc.uc_stack.ss_size = stack_size;
        makecontext(&uc, switch_fn, 0);
        raise(SIGUSR1);
 
-- 
2.17.1