General Category > Sol_Asm

writing to data or bss section variables

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bogdanontanu:
I will also be interested to see how you generated a .so  file with sol_asm ;)

bogdanontanu:
Hi mineiro,

There is a new Sol_Asm version that fixes some of the issues with MOV reg,[r12] or MOV reg,[r13] issues
http://www.oby.ro/sol_asm/files/sol_asm_2016_08_13_v36_38.zip

mineiro:
Hello sir Bogdan, thanks, I will test new version. This post is above old version ok.

I'm facing some problems when dealing with hll involving structures. I'm not being able to write to xmm register too.
I have a suggestion about procedures.
When calling a function, parameters are passed on registers, if parameters are bigger than 6 on linux64 or 4 on windows64, so on stack.
On entry of function we need something like 'shadow space' used on win64. I know we can use global variables or local variables, this is why it's just a suggestion.
If user don't need that stack frame (shadow space), he simple don't put arg inside function scope or just create a regular label.

Follows a code testcase:
issue.solasm

--- Code: ---.use64
section "text" class_code alias ".text"
section "data" class_data alias ".data"
section "bss"  class_bss  alias ".bss"

;changed to suit as an example.
STRUC ETH_PACKET
    packet_ptr              dq      ?
    packet_id               dq      ?
    packet_mac_src          rq      16
    packet_mac_dest         rq      16
ENDS

STRUC ETH_DRV
    drv_id                  dq      ?
    drv_name                rq      128
    eth_status              dq      ?
    packets_buff            rs      ETH_PACKET,2
ENDS

sys_exit equ 60

.entry _start

.data
my_driver       rs      ETH_DRV,1

;on entry, [rsp]=argc, [rsp+8]=ptr argv1, ...
.text
_start:
;[shadow space]----------------------------------------------------
  lea rbx,[rsp] ;argc
  mov rbx,[rbx]
  invoke my_proc,56 ;cdecl calling convention
  lea rax,[rsp]
  mov rax,[rax] ;;being overwrited
  cmp rax,rbx ;are not same
;------------------------------------------------------------------
;[structures]------------------------------------------------------
    mov     rsi,my_driver
    mov     rax,[rsi + ETH_DRV.packets_buff.packet_id]
    mov [rsi + ETH_DRV.packets_buff.packet_id],5 ;ok
    .if qword [rsi + ETH_DRV.packets_buff.packet_id] == 5 ;<----- here, its generating cmp qword [rsi],5
    nop
    .endif
;------------------------------------------------------------------
  mov rdi,0 ;native, system calls calling convention
  mov rax,sys_exit ;end this program
  syscall

public my_proc ;helps while debugging, can be done to variables too
proc my_proc lin64 ;cdecl calling convention
arg arg1 ;sub rsp,8 only one argument, max is 6 because others are on stack
  mov [arg1],rdi ;<----- this, a shadow space to store this argument||parameter
;add rsp,8
  ret
endp

/*
sol_asm issue.solasm issue.o -elf64
ld -m elf_x86_64 -o issue issue.o
rm issue.o
*/
--- End code ---

----------------------------------------------------------------------------------
Library have only exit (sair) function, command program will echo argc and argv. Please, this is just a test, I'm learning these things now, so, can have mistakes or errors ok.

sair.solasm

--- Code: ---.use64
section "text" class_code alias ".text"

;export sair
public sair
.text
align 16
sair:
;mov rdi,0
mov rax, 60 ;sys_exit
syscall

/*
sol_asm2 sair.solasm sair.o -elf64
ld -m elf_x86_64 -shared -o libsair.so sair.o
rm sair.o
*/

--- End code ---

command.solasm

--- Code: ---.use64
section "text" class_code alias ".text"
section "data" class_data alias ".data"
section "bss"  class_bss  alias ".bss"

;windows.obj == linux.o
;windows.dll == linux.so
;windows static.lib == linux static.a
;windows.sys == linux.ko
;windows eol CRLF == linux eol LF == mac eol LFCR??? ;end of line
;windows eos 00 == linux eos 00 ;end of string
;windows cmd line path "\" == linux cmd line path "/" ;path delimiter
;windows .bat||.cmd == linux .sh (on linux is need set execution by typing "chmod +x file.sh)

;rbx,rsp,rbp,r12-r13-r14-r15 calle saved register, preserved between calls
;rdi,rsi,rdx,rcx,r8,r9 dont preserved across calls, (cdecl calling convention, xmm registers ignored into this example)
;r10,r11,rax temp registers, don't saved across calls
;rax-rdx first and possible second return values

extern g_print lin64 ;glib2 function
extern sair lin64 ;sair (exit) function inside libsair.so

.entry _start

.data
elementos db "argc%d is %s",10,0

.text
_start:

  invoke main,[rsp],addr [rsp+8]
  invoke sair,45 ;return value, can be obtained using "echo $?"

public main
proc main lin64 ;this will echo command line parameters
local argc,argv
    mov [argc],rdi ;so we can use these registers for free, they are stored on memory
    mov [argv],rsi
    mov ebx,1
    .while rbx <= [argc]
      mov rdx,[argv]
      mov rdx,[rdx]
      invoke g_print,elementos,rbx ;on family of print functions on linux will print numbers, so rax contain how much xmm registers are used
;it's a good pratice zero rax register for safety by 'xor eax,eax' (more quickly on my tests than 'xor rax,rax' or 'mov rax,0' or 'and rax,0')
      add [argv],8
      inc ebx
    .endw
  ret
endp

;command line below
; -L. == local path to be searched to find libsair.so
; all libraries on linux start with 'lib' name, so on command line while linking we only need (if path environment are ok) -lsair that means libsair.so
; -L == library path
; -I == include path (not used here), used by C .h headers

;doit.sh
/*
sol_asm command.solasm command.o -elf64
ld -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -L/lib/x86_64-linux-gnu -L/usr/lib/x86_64-linux-gnu -L. -lglib-2.0 -lsair -o command command.o
rm command.o
./command one two 3 4 5 ; echo $?
*/

--- End code ---
You can change g_print to printf if your system does not have that library, change link switch -lglib-2.0 to -lc
I remember you write into some place about creating our own prologue and epilog macro, can you give some example?

I don't understand C language, so, I'm learning C by osmosis. I'm compiling and disassembling, after checking.
When I don't understand C .h headers, I get an example and full fill all structure variables and after do a dump while debugging to know sizeof members.
some usefull commands
;disassembler
objdump -d -Mintel command
objdump -s command
objdump -d -Mintel libsair.so
;lib dependecy
ldd command
ldd libsair.so
;data,functions, ...
nm command
nm libsair.so

while generating library we can append many object files like
ld -m elf_x86_64 -shared -o libsair.so sair.o other.o another.o ...
static libraries are build using 'ar' comand, I was not able to link using static library for a while, I know that I can extract specific object file inside static library (probably dependecy of variables, ... will be a trouble) but I like the right way.
Well, linux is open source, If I understand C language I will download C source code and study it, but I can't.

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