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

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

[Tom de Vries]

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
---
 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);

base-commit: 023b960d59c25994da233ea371deb26105fbacc8
-- 
2.35.3

Re: [pushed] [gdb/testsuite] Fix gdb.threads/schedlock.exp on fast cpu

[Tom de Vries]

On 2/6/23 12:54, Tom de Vries via Gdb-patches wrote:
> 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.
> 


Hmm, I just found out that this regresses the test-case with older 
compilers like 4.8 and 5, I'll need to fix that.

Thanks,
- Tom

> PR testsuite/30074
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30074
> ---
>   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);
> 
> base-commit: 023b960d59c25994da233ea371deb26105fbacc8