Re: Unwinding stack past main() when it has another name

[Steven Johnson <sjohnson@sakuraindustries.com>]

Daniel Jacobowitz wrote:

>On Fri, Jun 17, 2005 at 08:22:13AM -1100, Steven Johnson wrote:
>  
>
>>Daniel Jacobowitz wrote:
>>
>>    
>>
>>>The fact that we stop at _start is a feature, so hopefully you can rely
>>>on that in the future.
>>>
>>>For some non-C languages we get the name of the main function from
>>>debug information, but for C it's always main()
>>>
>>>
>>>      
>>>
>>This isnt always the case for embedded targets.  There is no RULE that C 
>>programs must have a main() function.  It may be that most do by 
>>convention, but they dont have to.  In fact, main() can be a pain for 
>>small embedded targets because it wants a return value and arguments, 
>>which mean nothing for a program that isnt "launched" by a user on 
>>demand, but the C compiler detects the special function name main() and 
>>objects if it doesnt have the standard format.  Programs dont even need 
>>to have an entry point called _start.  It all depends on how you set up 
>>your link map.
>>    
>>
>
>In fact you're wrong: there is a rule that C programs must have a
>main() function.  It's in the language standard.
>  
>
I stand corrected.  It is in fact in the standard as you say.  I have 
just been so exposed to code (written by many people) where the first C 
function that runs isnt called "main" it seemed to be a convention 
rather than a rule.  But as you say, many tool chains, gcc included 
allow for a program to not have a "main" function if you get in and 
modify the startup code and link map, which you often do for embedded 
targets, and doing so is not "standard" C.

>The fact that many embedded toolchains allow you to do things
>differently is outside the boundaries of the language standard, and if
>you don't have a main() your backtraces will stop at your entry point,
>determined from the ELF file.  GDB'll do the best it can.
>
>  
>
I wasnt suggesting GDB was broken in this regard, I was simply pointing 
out that not all (what Ive always considered to be) "C" programs have a 
main() function.

Steven