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diff --git a/dev/c/system.html b/dev/c/system.html new file mode 100644 index 0000000..65eede1 --- /dev/null +++ b/dev/c/system.html @@ -0,0 +1,159 @@ +<!DOCTYPE html> +<html dir="ltr" lang="en"> + <head> + <meta charset='utf-8'> + <title>System Development & GDB</title> + </head> + <body> + <a href="../index.html">Development Index</a> + + <h1>System Development</h1> + + <p>System development requires knowing how to debug + kernel know how, in this example will be used Qemu + and GDB. Qemu creates the virtual machine that kernel + will run on and GDB will connect to it to help us + understand how things tick.</p> + + <h2>Kernel Build</h2> + + <pre> + $ tar xf linux-4.9.48.tar.xz + $ cd linux-4.9.48 + </pre> + + <p>Default configuration disable some security + configurations that allow us to debug (random memory + layout).</p> + + <pre> + $ make x86_64_defconfig + </pre> + + <p>Enable CONFIG_DEBUG_INFO, CONFIG_DEBUG_INFO_DWARF4 + and CONFIG_GDB_SCRIPTS in the kernel;</p> + + <pre> + make x86_64_defconfig + cat <<EOF >.config-fragment + CONFIG_DEBUG_INFO=y + CONFIG_DEBUG_KERNEL=y + CONFIG_GDB_SCRIPTS=y + EOF + ./scripts/kconfig/merge_config.sh .config .config-fragment + </pre> + + <p>Check or change to your needs the configuration;</p> + <pre> + $ make nconfig + </pre> + + <p>Build Kernel and modules;</p> + + <pre> + $ make -j $(nproc) + </pre> + + <h2>Simple Init</h2> + + <p>Now that you have the kernel compiled you can + create a simple init program, this program is called + when kernel finish to load and setup its internals + and is ready to launch first process. + Init program should not exit or kernel will panic. + Create init.S;</p> + + <pre> + .global _start + _start: + mov $1, %rax + mov $1, %rdi + mov $message, %rsi + mov $message_len, %rdx + syscall + jmp . + message: .ascii "FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR\n" + .equ message_len, . - message + </pre> + + <p>Assemble, link and create simple initial ram disk;</p> + + <pre> + mkdir d + as --64 -o init.o init.S # assemble + ld -o d/init init.o # link + cd d + find . | cpio -o -H newc | gzip > ../rootfs.cpio.gz + </pre> + + <p>Clean temporary directory;</p> + + <pre> + cd .. + rm -r d/ + </pre> + + <p>Can be used C to create init program;</p> + + <pre> + #include <stdio.h> + #include <unistd.h> + + int main() { + printf("FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR\n"); + sleep(0xFFFFFFFF); + return 0; + } + </pre> + + <pre> + $ gcc -static init.c -o init + </pre> + + <h2>Start Debugging</h2> + + <p>Test qemu, kernel and simple init program, you + should see + "FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR FOOBAR";</p> + + <pre> + $ qemu-system-x86_64 -enable-kvm --kernel arch/x86_64/boot/bzImage \ + --initrd rootfs.cpio.gz + </pre> + + <p>If everything goes well you can start qemu without + starting the CPU (-S) and with gdb server on TCP port 1234 (-s).</p> + + <pre> + $ qemu-system-x86_64 -enable-kvm --kernel arch/x86/boot/bzImage \ + --initrd rootfs.cpio.gz \ + -S -s + </pre> + + <p>On another terminal start gdb;</p> + + <pre> + gdb \ + -ex "add-auto-load-safe-path $(pwd)" \ + -ex "file vmlinux" \ + -ex 'set arch i386:x86-64:intel' \ + -ex 'target remote localhost:1234' \ + -ex 'break start_kernel' \ + -ex 'continue' \ + -ex 'disconnect' \ + -ex 'set arch i386:x86-64' \ + -ex 'target remote localhost:1234' + </pre> + + + <a href="../index.html">Development Index</a> + <p> + This is part of the c9-doc Manual. + Copyright (C) 2016 + c9 team. + See the file <a href="../../fdl-1.3-standalone.html">Gnu Free Documentation License</a> + for copying conditions.</p> + + </body> + +</html> |