Re: Debugger thread dump confusion
Re: Debugger thread dump confusion
- Subject: Re: Debugger thread dump confusion
- From: Chris Smith <email@hidden>
- Date: Tue, 29 Aug 2006 08:33:16 +0100
On 29 Aug 2006, at 02:18, Shawn Erickson wrote:
On Aug 28, 2006, at 4:49 PM, Scott Ribe wrote:
Any ideas how to find the offending code (even though I know it's a
duff reference when the UTF8String message is sent to the null ref
user)? Shouldn't it show:
0 - objc_msgSend
1 - main
2 - start
Well, actually no, or maybe ;-)
- In Objective-C it's legal to send messages to nil. You might or
might not
get a useful return value (IIRC the rule is that if the method
returns an
object you get back nil, but if the method returns a C type the
return is
undefined. Even worse, there are cases where on PPC the 0'ish
value will be
returned, but not on Intel.)
"In Objective-C, it is valid to send a message to a nil object. The
Objective-C runtime assumes that the return value of a message sent
to a nil object is nil, as long as the message returns an object or
any integer scalar of size less than or equal to sizeof(void*).
On Intel-based Macintosh computers, messages to a nil object always
return 0.0 for methods whose return type is float, double, long
double, or long long. Methods whose return value is a struct, as
defined by the Mac OS X ABI Function Call Guide to be returned in
registers, will return 0.0 for every field in the data structure.
Other struct data types will not be filled with zeros. This is also
true under Rosetta. On PowerPC Macintosh computers, the behavior is
undefined."
<http://developer.apple.com/documentation/MacOSX/Conceptual/
universal_binary/universal_binary_tips/chapter_5_section_22.html>
Interesting.
In fact as stated by Scott Ribe, I'm actually passing the address of
the code which will bomb but for other reasons. The stack trace is
still useless. I mean Xcode (or more specifically gdb) should know
where main is, it should know that it is Obj-C code and it should
know how to deal with it. I've raised an issue - will see if I get
any luck.
Thanks all,
Chris Smith
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