C Inline Asm Int 0x10 - c

Question

I'm attempting to write a function that prints strings the screen in C. It's for a boot loader so there are no external libraries or anything linked in. Here's my function:
void printString(const char* pStr) {
while(*pStr) {
__asm__ __volatile__ (
"movb 0x0e, %%ah\n"
"movb %[c], %%al\n"
"int $0x10\n"
:
: [c] "r" (*pStr)
: "ax"
);
++pStr;
}
}
When I run this, I don't get any errors in my VM. It just sits there with the cursor in the upper left corner of the screen. Any thoughts? I can produce an objdump -d if anyone thinks it will be helpful.

Answer 1

Okay after some helpful comments, I may just go with full assembly. Something like
Print:
push %ax
movb $0x0E, %ah # Set interrupt code
movb $0x00, %bh # Set page #
.loop:
lodsb # Load next char
test %al, %al # Check for \0
je .done
int $0x10 # Call interrupt
jmp .loop
.done:
pop %ax
ret
That should be 16-bit real mode compatible and can be assembled with GAS, which, as I understand it, works better than GCC for compiling 16-bit programs.

Answer 2

I think you're missing the point. The problem isn't your assembly code; the problem is that "int 10" is a BIOS
If you've already booted to an OS (e.g. Windows or Linux), then your x86 CPU is running in "protected mode"; and you probably don't have access to int 10 from user space ... unless something like a Windows command prompt emulates it for you.
As far as Linux/assembly programming in general, I strongly recommend this (free, on-line, very good) book:
Programming from the Ground Up, Jonathan Bartlett
Thank you for clarifying that you're writing a "boot loader". Strong suggestion1: boot your custom code from a USB stick, or create a virtual DOS floppy to boot a DOS VM (either VMWare or VBox VMs, for example).
Here are some tutorials:
http://www.codeproject.com/Articles/36907/How-to-develop-your-own-Boot-Loader
https://cs.au.dk/~sortie/dopsys/osdev/
http://wiki.osdev.org/Rolling_Your_Own_Bootloader