Avoid sign extension in syscall return values.

2009-04-17  David Smith  <dsmith@redhat.com>

        * tapset/utrace.stp: Cast the return value of
        syscall_get_return_value() to an unsigned long to avoid sign
        extension.

1 files changed, 15 insertions, 9 deletions

diff --git a/tapset/utrace.stp b/tapset/utrace.stp
index 00f427e6..0d26ed5f 100644
--- a/tapset/utrace.stp
+++ b/tapset/utrace.stp
@@ -1,20 +1,26 @@
 /* utrace-only subset of register accessors */
 
-
 %{
 #include "syscall.h"
 %}
 
-function _utrace_syscall_nr:long () %{
-   THIS->__retvalue = syscall_get_nr(current, CONTEXT->regs); /* pure */
+function _utrace_syscall_nr:long () %{		/* pure */
+    THIS->__retvalue = syscall_get_nr(current, CONTEXT->regs);
 %}
 
-function _utrace_syscall_arg:long (n:long) %{
-   unsigned long arg = 0; /* pure */
-   syscall_get_arguments(current, CONTEXT->regs, (int)THIS->n, 1, &arg);
-   THIS->__retvalue = arg;
+function _utrace_syscall_arg:long (n:long) %{	/* pure */
+    unsigned long arg = 0;
+    syscall_get_arguments(current, CONTEXT->regs, (int)THIS->n, 1, &arg);
+    THIS->__retvalue = arg;
 %}
 
-function _utrace_syscall_return:long () %{
-   THIS->__retvalue = syscall_get_return_value(current, CONTEXT->regs); /* pure */
+function _utrace_syscall_return:long () %{	/* pure */
+    /*
+     * Here's the reason for the "unsigned long" cast.  Since all
+     * values inside systemtap are 64-bit numbers, return values were
+     * getting sign extended.  This caused return values to not match
+     * up with the same values passes as arguments.
+     */
+    THIS->__retvalue = (unsigned long)syscall_get_return_value(current,
+							       CONTEXT->regs);
 %}