From: Alex Zhuravlev <Alex.Zhuravlev@Sun.COM>
Date: Thu, 3 Jun 2010 05:01:14 +0000 (-0700)
Subject: Stack overflow on 64-bit modulus operations on 32-bit architectures.
X-Git-Tag: zfs-0.8.0-rc1~152^2~593
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=1b4ad25e2f29172c86d3293b61f0c5232d4a2da8;p=zfs

Stack overflow on 64-bit modulus operations on 32-bit architectures.

Running 'zpool create' on a 32-bit machine with an SPL compiled with
gcc 4.4.4 led to a stack overlow.  This turned out to be due to some
sort of 'optimization' by gcc:

uint64_t __umoddi3(uint64_t dividend, uint64_t divisor)
{
   return dividend - divisor * (dividend / divisor);
}

This code was supposed to be using __udivdi3 to implement /, but gcc
instead implemented it via __umoddi3 itself.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
---

diff --git a/module/spl/spl-generic.c b/module/spl/spl-generic.c
index 29b698889..9916051de 100644
--- a/module/spl/spl-generic.c
+++ b/module/spl/spl-generic.c
@@ -96,7 +96,8 @@ EXPORT_SYMBOL(highbit);
  * Implementation of 64 bit division for 32-bit machines.
  */
 #if BITS_PER_LONG == 32
-uint64_t __udivdi3(uint64_t dividend, uint64_t divisor)
+uint64_t
+__udivdi3(uint64_t dividend, uint64_t divisor)
 {
 #if defined(HAVE_DIV64_64) /* 2.6.22 - 2.6.25 API */
 	return div64_64(dividend, divisor);
@@ -125,9 +126,10 @@ EXPORT_SYMBOL(__udivdi3);
 /*
  * Implementation of 64 bit modulo for 32-bit machines.
  */
-uint64_t __umoddi3(uint64_t dividend, uint64_t divisor)
+uint64_t
+__umoddi3(uint64_t dividend, uint64_t divisor)
 {
-	return dividend - divisor * (dividend / divisor);
+	return (dividend - (divisor * __udivdi3(dividend, divisor)));
 }
 EXPORT_SYMBOL(__umoddi3);
 #endif /* BITS_PER_LONG */