[binutils-gdb] [gdb/testsuite] Fix gdb.threads/schedlock.exp on fast cpu

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=9af467b82406614deb46151f838c336a7c8604db

commit 9af467b82406614deb46151f838c336a7c8604db
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Feb 6 12:52:50 2023 +0100

    [gdb/testsuite] Fix gdb.threads/schedlock.exp on fast cpu
    
    Occasionally, I run into:
    ...
    (gdb) PASS: gdb.threads/schedlock.exp: schedlock=on: cmd=continue: \
      set scheduler-locking on
    continue^M
    Continuing.^M
    PASS: gdb.threads/schedlock.exp: schedlock=on: cmd=continue: \
      continue (with lock)
    [Thread 0x7ffff746e700 (LWP 1339) exited]^M
    No unwaited-for children left.^M
    (gdb) Quit^M
    (gdb) FAIL: gdb.threads/schedlock.exp: schedlock=on: cmd=continue: \
      stop all threads (with lock) (timeout)
    ...
    
    What happens is that this loop which is supposed to run "just short of forever":
    ...
        /* Don't run forever.  Run just short of it :)  */
        while (*myp > 0)
          {
            /* schedlock.exp: main loop.  */
            MAYBE_CALL_SOME_FUNCTION(); (*myp) ++;
          }
    ...
    finishes after 0x7fffffff iterations (when a signed wrap occurs), which on my
    system takes only about 1.5 seconds.
    
    Fix this by:
    - changing the pointed-at type of myp from signed to unsigned, which makes the
      wrap defined behaviour (and which also make the loop run twice as long,
      which is already enough to make it impossible for me to reproduce the FAIL.
      But let's try to solve this more structurally).
    - changing the pointed-at type of myp from int to long long, making the wrap
      unlikely.
    - making sure the loop runs forever, by setting the loop condition to 1.
    - making sure the loop still contains different lines (as far as debug info is
      concerned) by incrementing a volatile counter in the loop.
    - making sure the program doesn't run forever in case of trouble, by adding an
      "alarm (30)".
    
    Tested on x86_64-linux.
    
    PR testsuite/30074
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30074

Diff:
---
 gdb/testsuite/gdb.threads/schedlock.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/gdb/testsuite/gdb.threads/schedlock.c b/gdb/testsuite/gdb.threads/schedlock.c
index 5422c64fd99..c4e77948ad4 100644
--- a/gdb/testsuite/gdb.threads/schedlock.c
+++ b/gdb/testsuite/gdb.threads/schedlock.c
@@ -24,7 +24,7 @@ void *thread_function(void *arg); /* Pointer to function executed by each thread
 
 #define NUM 1
 
-unsigned int args[NUM+1];
+unsigned long long int args[NUM+1];
 
 int main() {
     int res;
@@ -32,6 +32,8 @@ int main() {
     void *thread_result;
     long i;
 
+    alarm (30);
+
     for (i = 1; i <= NUM; i++)
       {
 	args[i] = 1;
@@ -72,13 +74,14 @@ volatile int call_function = 0;
 
 void *thread_function(void *arg) {
     int my_number =  (long) arg;
-    int *myp = (int *) &args[my_number];
+    unsigned long long int *myp = (unsigned long long int *) &args[my_number];
+    volatile unsigned int cnt = 0;
 
-    /* Don't run forever.  Run just short of it :)  */
-    while (*myp > 0)
+    while (1)
       {
 	/* schedlock.exp: main loop.  */
 	MAYBE_CALL_SOME_FUNCTION(); (*myp) ++;
+	cnt++;
       }
 
     pthread_exit(NULL);