Author Topic: vsprintf() doesn't work (Read 9091 times)

compu · « **on:** February 24, 2011, 01:42:29 pm »

Hey, I wanted to make an on-screen console for the nspire.
Normal text output works fine, but i wanted an sprintf()-like function to output text, so I made this function:

Code: [Select]

void c_swrite(struct console *c, char* format, int len, char bgColor, char textColor, ...)
{
	char buf[len];
	memset(buf,'\0',sizeof(char)*len);
	va_list arglist;
	va_start(arglist,textColor);
	vsprintf(buf,format,arglist);
	c_write(c,buf,bgColor,textColor);
	va_end(arglist);
}

Always when this function reaches vsprintf, the emulator crashes.

Code: [Select]

Error at PC=102F45C0: Unaligned read_word: 1800e0ed
         Backtrace:
Frame     PrvFrame Self     Return   Start
1800E0B0: 1800E0E8 1800E0B4 1106E9DC 102F4210
1800E0E8: 1109CA20 00000000 1800E934 1106E5A4

I have attached my whole source.
So, what am I doing wrong?

Goplat · « **Reply #1 on:** February 24, 2011, 02:47:20 pm »

Ndless's definition of va_start is not quite correct, it doesn't take into account that a 1-byte function parameter actually takes up 4 bytes on the stack.

For the time being, try using the gcc intrinsic __builtin_va_start instead.

compu · « **Reply #2 on:** February 24, 2011, 02:56:10 pm »

Do you mean I should do it like this:

Code: [Select]

void c_swrite(struct console *c, char* format, int len, char bgColor, char textColor, ...)
{
	char buf[len];
	memset(buf,'\0',sizeof(char)*len);
	__builtin_va_list arglist;
	__builtin_va_start(arglist,textColor);
	__builtin_vsprintf(buf,format,arglist);
	c_write(c,buf,bgColor,textColor);
	__builtin_va_end(arglist);
}

I can compile it without any errors, but the emulator still crashes

Goplat · « **Reply #3 on:** February 24, 2011, 03:11:50 pm »

Don't use __builtin_vsprintf, that would end up trying to call an actual function called vsprintf (rather than the syscall). It looks like yagarto's gcc is annoyingly strict about how you can use a __builtin_va_list, but this still works:

vsprintf(buf,format,*(char **)&arglist);

compu · « **Reply #4 on:** February 24, 2011, 03:17:56 pm »

Thanks!

This works fine

ExtendeD · « **Reply #5 on:** February 25, 2011, 04:44:47 pm »

Thanks, Ndless's va_* definitions are now wrappers to GCC builtin functions.

Author Topic: vsprintf() doesn't work (Read 9091 times)

compu

vsprintf() doesn't work

Goplat

Re: vsprintf() doesn't work

compu

Re: vsprintf() doesn't work

Goplat

Re: vsprintf() doesn't work

compu

Re: vsprintf() doesn't work

ExtendeD

Re: vsprintf() doesn't work