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Re: [avr-gcc-list] strange c++ obiect initialization problems (full code

From: Georg-Johann Lay
Subject: Re: [avr-gcc-list] strange c++ obiect initialization problems (full code included)
Date: Sat, 11 Jun 2011 10:56:15 +0200
User-agent: Mozilla Thunderbird 1.0.7 (Windows/20050923)

Marcin S schrieb:
2011/6/9 Georg-Johann Lay <address@hidden>:

Marcin S schrieb:

Hello there,

from time to time i have a strange problems when initializing
class objects in file range by their respective constructors, i
noted that problem occurs only when that constructors takes
pointers to other global objects, tables or something else.

Whats the problem? in best scenario object pointer are wrongly
set and pointing to some random locations, at worst my program
does not start at all (event with my main() func empty) it just

here is link to my code http://dl.dropbox.com/u/6883398/Lays.tar.bz2 its and eclipse
project, simple "make" in project directory should work too. Note
that archive contains already compiled program in "Release"
directory, this compilation does not work at all! (worst case
scenario described above).

As I wrote this program incrementaly it stopped working after i
added 2 objects inits in layouts.cpp

minTag(minTagData,strMin,true,CLayPGMString::XSMALL); CLayPGMString

strMin and strMax params are pointers to strings in PROGMEM, if i
 replace it with zeros like

CLayPGMString minTag(minTagData,0,true,CLayPGMString::XSMALL); CLayPGMString maxTag(maxTagData,0,true,CLayPGMString::XSMALL);

program starts again.

Other important thing noted is, when I initialise those objects
in file range with their default, empty constructors and then set
needed pointers at run time (for example right after main()
function) everything works too. I ran out of ideas what could be
wrong, maybe wrong code, I'm open to any suggestions.

I'm using avr-gcc-4.5.2 on gentoo linux, also checked on stable
4.4 and it behaves exactly the same way.


Do you see r20 used in one of the functions? Reminds me of http://gcc.gnu.org/PR45263 which is not yet backported to avr-gcc <


Hej Johann,

I'm not sure if i checked it correctly, I've opened .lss file corresponding to my program and yes, there are some r20 operations in
 this function.

Excuse me my lack of knowledge of low lvl stuff, but You think this might cause the problem?

That depends on the hardware you use. The problem will not occur on devices <= 64 kib flash. Look at the code again. In the startup code that runs before main you might see use of r20 around calls to you function. Note that these calls will be indirect, so searching for symbol will not help. Using r20 that way in startup can cause problems because is is callee-used register and the callee can clobber it, leaving its content in a mess in startup code.



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