Backport #6736: Avoid misoptimization due to division by zero

• Status: Closed
• Assignee: naruse (Yui NARUSE)

[xi (Xi Wang)]

In time.c (quo) we have:

    if (b == 0) rb_num_zerodiv();
    c = a / b;

This code pattern is dangerous. Some C compilers may move the division before the check because:

1. It appears to the compiler that the division a / b is always reachable even with b == 0 (though rb_num_zerodiv invokes rb_raise internally).

2. Division by zero is undefined behavior.

This happened to PostgreSQL before.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=616180

Attached patch marks rb_num_zerodiv as NORETURN to avoid this issue.

[shyouhei (Shyouhei Urabe)]

The patch seems OK to me.

[kosaki (Motohiro KOSAKI)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r36454.
Xi, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• include/ruby/intern.h (rb_num_zerodiv): Added NORETURN.
  Patched by Xi Wang. [Bug #6736]

[kosaki (Motohiro KOSAKI)]

• Tracker changed from Bug to Backport
• Project changed from Ruby master to Backport193
• Category deleted (core)
• Target version deleted (2.0.0)

Committed. And I believe this should be backported into 1.9.x.

[ktsj (Kazuki Tsujimoto)]

• Status changed from Closed to Assigned
• Assignee set to naruse (Yui NARUSE)

[naruse (Yui NARUSE)]

• Status changed from Assigned to Closed

This issue was solved with changeset r36552.
Xi, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

merge revision(s) 36454:

* include/ruby/intern.h (rb_num_zerodiv): Added NORETURN.
  Patched by Xi Wang. [Bug #6736]