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Linux Notes

1 Kernel

1.1 Kernel startup (for X86 and ARM)

1.2 Scheduler

1.3 MM

1.4 Network

1.5 Video

1.6 Devices

1.6.1 USB

1.6.2 TTY

1.7 syscall (x86)

  • syscall initialization procedure
    • setup()
      • startp_32()
        • start_kernel() (from init/main.c)
          • trap_init()
            • set_system_trap_gate(SYSCALL_VECTOR, &system_call);
              • arch/x86/include/asm/irq_vectors.h # define SYSCALL_VECTOR 0x80
    • Or do a syscall using sysenter, syscall etc (vdso, AT_SYSINFO, __kernel_vsyscall …)
      • linux-2.6/arch/x86/vdso/vdso32-setup.c
      • linux-2.6/arch/x86/vdso/vdso32/{syscall,sysenter,int80}.S
      • linux-2.6/arch/x86/vdso/vdso32/vdso32.lds.S
  • syscall flow for execve
    • sys_execve() (from arch/x86/kernel/process.c)
      • do_execve(filename, argv, envp, regs)
        • Sanity checks
        • open_exec(filename)
        • prepare_binprm(bprm) Reads permission and stuff
        • copy_strings() Copy environment, args etc
        • search_binary_handler(bprm,regs) Search for the executable type and its handler
          • load_elf_binary()
            • Do some sanity checks
            • Read in all the elf sections
            • Map the read elf sections
            • load_elf_interp()
              • Loads the interpreter mentioned in the elf (for example /lib/ld-linux.so)
            • start_thread()
              • Sets up the USER_CS. Sets IP and SP to be that of the interpreter’s entry points (in our case it is _dl_start() of ld-linux.so)
      • RTLD_START (glibc/sysdeps/i386/dl-machine.h)
        • _dl_start() (glibc/elf/rtld.c)
          • elf_machine_load_address ()
            • Runtime load address of the linker
          • Read the linker’s own header
          • Allocate TLS
          • ELF_DYNAMIC_RELOCATE ()
            • elf_machine_runtime_setup () (glibc/sysdeps/i386/dl-machine.h)
              • If we are doing “lazy” on-demand binding, setup the appropriate handlers (_dl_runtime_resolve or _dl_runtime_profile)
            • ELF_DYNAMIC_DO_REL () (glibc/elf/dynamic-link.h)
              • elf_dynamic_do_rel()
                • If laze relocation, call elf_machine_lazy_rel() (at glibc/sysdeps/i386/dl-machine.h). Set up to call _dl_runtime_resolve.
            • ELF_DYNAMIC_DO_RELA () (glibc/elf/dynamic-link.h)
          • _dl_start_final()
            • Record the startup time
            • __builtin_frame_address (0)
            • _dl_sysdep_start() (glibc/elf/dl-sysdep.c)
              • Initialize user entry point i.e., ENTRY_POINT (which is nothing but _start). It will be updated to a value specified by AT_ENTRY if one was supplied by the elf binary
              • dl_main() (from glibc/elf/rtld.c)
                • process_envvars()
                • See if the ld.so was run directly (rather than being invoked on behalf of an elf’s PT_INTERP section). If so, support the “ld.so programname args” kind of invocation. Loaded program’s PT_INTERP would be ignored, as we are the interpreter.
                • Or else: call _dl_new_object() Create a link map for executable
                • Scan through the header looking for dynamic section and initialize appropriate values in the create map object.
                • elf_get_dynamic_info ()
                • _dl_setup_hash ()
                • If we were just called to verify (“–verify”), exit now
                • _dl_init_paths
                • Load debug sections, setup debugging (for self as well)
                • Load all the objects, including LD_PRELOADS and DT_NEEDED objects
                • _dl_receive_error () for reporting missing dependencies
                • If we were just called to list the libraries (“–list”), list them and call it quits
                • If we are prelinked, update the conflicts and do call _dl_resolve_conflicts()
                • Else
                  • For each library object in the list
                    • Call _dl_relocate_object() which will do the relocation as needed (lazy etc - _dl_runtime_resolve() is the one that is of interest here). And also mprotect’ing of segments are done here.
              • return user_entry
            • Return what ever value _dl_sysdep_start() returned (that is the starting address of the binary)
          • Return the user start address
        • Setup the stack
        • Call _dl_init_internal_*()
        • Jump to the user start address
          • Setup stack
          • __libc_start_main() (glibc/csu/libc-start.c)
            • INIT_ARGV_and_ENVIRON
            • _dl_aux_init ()
            • __libc_csu_irel ()
            • __pthread_initialize_minimal ()
            • _dl_setup_stack_chk_guard ()
            • __cxa_atexit (…rtld_fini, ....)
              • Register destructor call back of the dynamic linker if any
            • __libc_init_first (argc, argv, __environ)
            • __cxa_atexit (… fini, …)
              • Register destructor call back of the program if any
            • __libc_check_standard_fds ()
            • init (argc, argv, __environ MAIN_AUXVEC_PARAM)
            • result = main (argc, argv, __environ MAIN_AUXVEC_PARAM)
              • Life revolves around here
            • exit (result)
              • __run_exit_handlers (status, &__exit_funcs, true)
                • Call the functions that were registered with “atexit()” and “onexit()”. Cleanup stdio.
                • RUN_HOOK (__libc_atexit, ())
                • _exit()
                  • syscall for __NR_exit_group

1.8 To Read

2 XServer

2.1 To Read

2.2 Xorg general architecture

2.3 Xorg and OpenGL

2.3.1 TinyGL

2.4 Intumo

2.4.1 to-be-checked

2.4.1.1 canvas http://live.gnome.org/ProjectRidley/CanvasOverview

2.4.1.2 Native widget drawing in canvas - QGraphicsView

2.4.1.3 Physics engine:

2.4.1.3.1 @Simon: “poorer” in which sense? have you tried writing a demo like TAT’s? have you tried using shaders? a physics engine? Clutter is already a competitive mobile UI tool.
2.4.1.3.2 @krh, yep - also see box2d and chipmonk. Pippin has been playing with them all (http://www.murrayc.com/blog/permalink/2008/03/03/clutter-tutorial-done-for-now/)

2.4.2 clutter

2.4.2.1 Q: Offscreen rendering support?

2.4.3 xserver

2.4.4 QUESTIONS:

2.4.4.1 Why not use Qt and custom widgets on top of it?

2.4.4.2 Why not use GTK and custom widgets on top of it?

2.4.4.3 Framebuffer and X11 comparison: http://www.vanille-media.de/site/index.php/2007/12/08/framebuffer-vs-x11/

2.4.4.3.1 Some tests http://svn.o-hand.com/repos/misc/trunk/fstests/

2.4.4.4 what is libggi?

2.4.4.4.1 comment from somewhere: Lucas wrote: A good compromise I found for a touchscreen based POS system (using one of those VIA mini-ATX boards) was libggi. It allows to develop and test on X and have the same binary run under fb.

2.4.4.5 what is this http://xynth.org/ ?

2.4.4.6 check qtopia

2.4.4.7 check http://www.freesmartphone.org/index.php/Specifications

2.4.4.8 check http://www.angstrom-distribution.org/

2.4.4.9 check http://www.vanille-media.de/site/index.php/2007/12/05/usability-through-bling/

2.4.4.10 check clutter

2.4.4.11 check cocoa

2.4.4.12 read X11 log in computer/laptop

2.4.4.13 read http://en.wikipedia.org/wiki/Display_resolution

2.4.4.14 nano x http://www.microwindows.org/

2.4.4.15 http://www.minigui.org/

2.4.4.16 http://fltk.org - Fast Light ToolKit

3 Miscellaneous

3.1 Tinyelf

[suresh@linux-vrse tt]$ cat | gcc -nostdlib -x c - -o helloworld
#define SYS_exit  1
#define SYS_write 4
#define stdout    1

int strlen(const char *str)
{
  long len = 0;
  while (str && *str++)
  {
      len++;
  }
  
  return len;
}


void print(const char *str) 
{
    int len = strlen(str);

    long ret;

    /* Can't touch ebx directly, PIC uses it */
    __asm__ __volatile__ ("pushl %%ebx\n"
                          "movl  %%esi, %%ebx\n"
                          "int	 $0x80\n;"
                          "popl  %%ebx"
                          :
                          : "a" (SYS_write),
                            "S" ((long) stdout),
                            "c" ((long) str),
                            "d" ((long) len));
    return;
}

void _start()
{
  main();

  __asm__ __volatile__ (
       "xorl %%ebx, %%ebx\n"
       "int $0x80\n"
       :
       : "a" (SYS_exit));
}

int main()
{
  print("Hello World\n");
  return 0;
}

[suresh@linux-vrse tt]$ strip -R .comment -R .comment.SUSE.OPTs -R .note.gnu.build-id helloworld
[suresh@linux-vrse tt]$ ll helloworld 
-rwxr-xr-x 1 suresh users 540 2010-07-21 13:19 helloworld

[suresh@linux-vrse tt]$ ./helloworld 
Hello World

3.2 VDSO

Dump of VDSO related stuff

[suresh@linux-vrse tmp]$ ldd /bin/cat 
        linux-gate.so.1 =>  (0xffffe000)
        libc.so.6 => /lib/libc.so.6 (0xb7e65000)
        /lib/ld-linux.so.2 (0xb7fe0000)

[suresh@linux-vrse tmp]$ LD_SHOW_AUXV=1 /bin/cat | grep AT_SYSINFO
AT_SYSINFO:      0xffffe414
AT_SYSINFO_EHDR: 0xffffe000

[suresh@linux-vrse tmp]$ cat /proc/self/maps  | grep vdso
ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]


[suresh@linux-vrse tmp]$ dd if=/proc/self/mem of=vdso skip=$((0xffffe000/0x1000)) count=1 bs=$((0x1000))
1+0 records in
1+0 records out
4096 bytes (4.1 kB) copied, 4.3047e-05 s, 95.2 MB/s

[suresh@linux-vrse tmp]$ objdump -d --start-address=0xffffe000 ./vdso 

/tmp/vdso:     file format elf32-i386


Disassembly of section .text:

ffffe400 <__kernel_sigreturn>:
ffffe400:       58                      pop    %eax
ffffe401:       b8 77 00 00 00          mov    $0x77,%eax
ffffe406:       cd 80                   int    $0x80
ffffe408:       90                      nop    
ffffe409:       8d 76 00                lea    0x0(%esi),%esi

ffffe40c <__kernel_rt_sigreturn>:
ffffe40c:       b8 ad 00 00 00          mov    $0xad,%eax
ffffe411:       cd 80                   int    $0x80
ffffe413:       90                      nop    

ffffe414 <__kernel_vsyscall>:
ffffe414:       51                      push   %ecx
ffffe415:       52                      push   %edx
ffffe416:       55                      push   %ebp
ffffe417:       89 e5                   mov    %esp,%ebp
ffffe419:       0f 34                   sysenter 
ffffe41b:       90                      nop    
ffffe41c:       90                      nop    
ffffe41d:       90                      nop    
ffffe41e:       90                      nop    
ffffe41f:       90                      nop    
ffffe420:       90                      nop    
ffffe421:       90                      nop    
ffffe422:       eb f3                   jmp    ffffe417
<__kernel_vsyscall+0x3>
ffffe424:       5d                      pop    %ebp
ffffe425:       5a                      pop    %edx
ffffe426:       59                      pop    %ecx
ffffe427:       c3                      ret    

[suresh@linux-vrse tmp]$ # or we can use
[suresh@linux-vrse tmp]$ dd if=/proc/self/mem of=- skip=$((0x`cat /proc/self/maps | grep vdso | cut -d'-' -f1`/0x1000)) count=1 bs=$((0x1000)) | objdump -d --start-address=0xffffe000 -

3.3 ELF format

3.4 Stack

3.5 BIOS

3.5.1 Coreboot