assembly - Baking PI with C and basic libs -

assembly - Baking PI with C and basic libs -

i have next problem - i've done baking pi course of study without problems , 've decided link pure asm c. , have done , working nice far decided utilize function sprintf convert int char*. when im trying compile im enjoying next error

ctesty.c:(.text+0x20): undefined reference 'sprintf' make: *** [build/output.elf] error 1

of course of study have included stdio.h, tried include lib straight in makefile without success.

you want link libc.so. seek adding -lc in link step in makefiles.

update after improve understanding of question

the baking pi examples build kernel.img runs in place of usual linux kernel. means c standard library not available. you'll need supply own sprintf() implementation, e.g.:

adapt bsd licensed ee_printf.c remove uart_send_char() adapt ee_printf() sprintf() making buf function parameter

why userspace libc wouldn't work without source modifications in kernel

conceptually:

the c standard library contains facilities dealing dynamic memory allocation (malloc, free), file scheme (fopen, fclose , of stdio), environment variables (getenv), error handling facilities setjmp longjmp , more. consider: how implement malloc in programme running under operating system? answer: you'd need interface request additional memory os, such brk, sbrk , mmap under linux. in os kernel, brk, mmap etc wouldn't right interfaces allocate memory. thus though non-toy kernels provide malloc facilities, won't able utilize userspace malloc implementations unmodified. in os kernel, functions fopen, getenv not useful. kernel writers take not include them. thus kernels don't include finish c standard library implementations functions kernel writers find useful.

in more mechanical sense:

the baking pi makefile produces kernel elf image command $(armgnu)-ld --no-undefined $(objects) -map $(map) -o $(build)output.elf -t $(linker). doesn't link build/output.elf libc implementation linker wouldn't able find symbol named sprintf. when build programme gcc t.c -o t, gcc implicitly links in libc unless alternative -nostdlib passed.

but conceptually of import points are:

the parts of c standard library useful in kernel require different implementations a lot of other parts of libc wouldn't useful in kernel

there c standard library implementations targeting bare metal environments. see example, newlib.

c assembly arm mingw yagarto