Here's the deal. I have an executable program that consists of 3 object files put together. 2 of the object files are compiled assembly code and 1 is a C source code file. They all compile together fine with gcc, but when I execute the program from a MS-DOS prompt is where the trouble is. Based on the main assembler code file (test1.asm), I move a value into the eax register, and then call the print_string function, which in turn calls the C function printf. At this point, I should see that value display on the screen, but I don't. Can anyone see anything obvoius in this code which would be causing this problem?
TEST1.ASM
*****************************************
; file: test1.asm
; First assembly program testing the ability
; to store data in the EAX register and print
; it to the screen.
;
; Syntax to create executable using DJGPP:
; nasm -f coff test1.asm
; gcc -o test1 test1.o driver.c asm_io.o
%include "e:\djgpp\asm_io.inc"
; initialized data should be placed under
; the .data segment
segment .data
output1 db "Hello World ", 0 ;space after string = null terminator
segment .bss
segment .text
global _asm_main
_asm_main:
enter 0,0
pusha
; begin program code
mov eax, output1 ; prepare variable for output
call print_string ; invoke asm proc that calls C
; end program code
; all below information required
popa
mov eax,0 ; return back to C
leave
ret
*****************************************
print_string function in asm_io.asm
*****************************************
print_string:
enter 0,0
pusha
pushf
push eax
push dword string_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
*****************************************
DRIVER.C
*****************************************
int asm_main(void);
int main()
{
int ret_status;
ret_status = asm_main();
return ret_status;
}
*****************************************
code not outputting data string
-
Curufir
Re:code not outputting data string
Code: Select all
push dword string_format
This is the only place I see it in your code.
Mind you, nasm should moan about it being used without being set first, so I don't see this as being the main problem seeing as you say it compiles ok.
-
Stephen
Re:code not outputting data string
The asm_io.asm file contains the string_format declaration. But if that's all that seems to be the problem, then can anyone else think of any platform specific issues I might be having here?
-
Pype.Clicker
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Re:code not outputting data string
what is obvious to me is that
- you might prefer using pushad/popad instead of pusha/popa while some version of nasm have been encoding "pusha" as 16-bits-overriden, iirc (or was it just for iret. dunno...)
- do you have some constant characters in your "format string" that you see or is it just "%s" ? -- just to make sure things works on a simpler environment...
- do you have the evidence the strings and the code get included in your kernel ?
- you might prefer using pushad/popad instead of pusha/popa while some version of nasm have been encoding "pusha" as 16-bits-overriden, iirc (or was it just for iret. dunno...)
- do you have some constant characters in your "format string" that you see or is it just "%s" ? -- just to make sure things works on a simpler environment...
- do you have the evidence the strings and the code get included in your kernel ?
-
Curufir
Re:code not outputting data string
Ok, my C is rusty, but isn't the printf declaration something like:
I only point this out because string_format must be a zero terminated string as well. Without that 0 the printf function will wander off into the wilderness when it tries to read the format string, probably breaking itself in the process and not performing the print.
Far as I can see you push the two memory references in the right order, how about testing the return value of printf (ie EAX) (Assuming it does actually return). Should be a 1 for correct operation I think.
Is "extern _printf" declared in asm_io.asm as well?
Code: Select all
extern int printf(const char *, ...);
Far as I can see you push the two memory references in the right order, how about testing the return value of printf (ie EAX) (Assuming it does actually return). Should be a 1 for correct operation I think.
Is "extern _printf" declared in asm_io.asm as well?
-
Stephen
Re:code not outputting data string
Here is the asm_io.asm file - the piece of code I did not place on here. This way, everyone can see for themselves. This is the first portion of the file:
;
; file: asm_io.asm
; Assembly I/O routines
; To assemble for DJGPP
; nasm -f coff -d COFF_TYPE asm_io.asm
; To assemble for Borland C++ 5.x
; nasm -f obj -d OBJ_TYPE asm_io.asm
; To assemble for Microsoft Visual Studio
; nasm -f win32 -d COFF_TYPE asm_io.asm
; To assemble for Linux
; nasm -f elf -d ELF_TYPE asm_io.asm
%define NL 10
%define CF_MASK 00000001h
%define PF_MASK 00000004h
%define AF_MASK 00000010h
%define ZF_MASK 00000040h
%define SF_MASK 00000080h
%define DF_MASK 00000400h
%define OF_MASK 00000800h
;
; Linux C doesn't put underscores on labels
;
%ifdef ELF_TYPE
%define _scanf scanf
%define _printf printf
%define _getchar getchar
%define _putchar putchar
%define _fputs fputs
%endif
%ifdef OBJ_TYPE
segment .data public align=4 class=data use32
%else
segment .data
%endif
int_format db "%i", 0
string_format db "%s", 0
reg_format db "Register Dump # %d", NL
db "EAX = %.8X EBX = %.8X ECX = %.8X EDX = %.8X", NL
db "ESI = %.8X EDI = %.8X EBP = %.8X ESP = %.8X", NL
db "EIP = %.8X FLAGS = %.4X %s %s %s %s %s %s %s", NL
db 0
carry_flag db "CF", 0
zero_flag db "ZF", 0
sign_flag db "SF", 0
parity_flag db "PF", 0
overflow_flag db "OF", 0
dir_flag db "DF", 0
aux_carry_flag db "AF", 0
unset_flag db " ", 0
mem_format1 db "Memory Dump # %d Address = %.8X", NL, 0
mem_format2 db "%.8X ", 0
mem_format3 db "%.2X ", 0
stack_format db "Stack Dump # %d", NL
db "EBP = %.8X ESP = %.8X", NL, 0
stack_line_format db "%+4d %.8X %.8X", NL, 0
math_format1 db "Math Coprocessor Dump # %d Control Word = %.4X"
db " Status Word = %.4X", NL, 0
valid_st_format db "ST%d: %.10g", NL, 0
invalid_st_format db "ST%d: Invalid ST", NL, 0
empty_st_format db "ST%d: Empty", NL, 0
;
; code is put in the _TEXT segment
;
%ifdef OBJ_TYPE
segment text public align=1 class=code use32
%else
segment .text
%endif
global read_int, print_int, print_string, read_char
global print_char, print_nl, sub_dump_regs, sub_dump_mem
global sub_dump_math, sub_dump_stack
extern _scanf, _printf, _getchar, _putchar, _fputs
read_int:
enter 4,0
pusha
pushf
lea eax, [ebp-4]
push eax
push dword int_format
call _scanf
pop ecx
pop ecx
popf
popa
mov eax, [ebp-4]
leave
ret
print_int:
enter 0,0
pusha
pushf
push eax
push dword int_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
print_string:
enter 0,0
pusha
pushf
push eax
push dword string_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
read_char:
enter 4,0
pusha
pushf
call _getchar
mov [ebp-4], eax
popf
popa
mov eax, [ebp-4]
leave
ret
print_char:
enter 0,0
pusha
pushf
push eax
call _putchar
pop ecx
popf
popa
leave
ret
print_nl:
enter 0,0
pusha
pushf
push dword 10 ; 10 == ASCII code for \n
call _putchar
pop ecx
popf
popa
leave
ret
sub_dump_regs:
enter 4,0
pusha
pushf
mov eax, [esp] ; read FLAGS back off stack
mov [ebp-4], eax ; save flags
;
; show which FLAGS are set
;
test eax, CF_MASK
jz cf_off
mov eax, carry_flag
jmp short push_cf
cf_off:
mov eax, unset_flag
push_cf:
push eax
test dword [ebp-4], PF_MASK
jz pf_off
mov eax, parity_flag
jmp short push_pf
pf_off:
mov eax, unset_flag
push_pf:
push eax
test dword [ebp-4], AF_MASK
jz af_off
mov eax, aux_carry_flag
jmp short push_af
af_off:
mov eax, unset_flag
push_af:
push eax
test dword [ebp-4], ZF_MASK
jz zf_off
mov eax, zero_flag
jmp short push_zf
zf_off:
mov eax, unset_flag
push_zf:
push eax
test dword [ebp-4], SF_MASK
jz sf_off
mov eax, sign_flag
jmp short push_sf
;
; file: asm_io.asm
; Assembly I/O routines
; To assemble for DJGPP
; nasm -f coff -d COFF_TYPE asm_io.asm
; To assemble for Borland C++ 5.x
; nasm -f obj -d OBJ_TYPE asm_io.asm
; To assemble for Microsoft Visual Studio
; nasm -f win32 -d COFF_TYPE asm_io.asm
; To assemble for Linux
; nasm -f elf -d ELF_TYPE asm_io.asm
%define NL 10
%define CF_MASK 00000001h
%define PF_MASK 00000004h
%define AF_MASK 00000010h
%define ZF_MASK 00000040h
%define SF_MASK 00000080h
%define DF_MASK 00000400h
%define OF_MASK 00000800h
;
; Linux C doesn't put underscores on labels
;
%ifdef ELF_TYPE
%define _scanf scanf
%define _printf printf
%define _getchar getchar
%define _putchar putchar
%define _fputs fputs
%endif
%ifdef OBJ_TYPE
segment .data public align=4 class=data use32
%else
segment .data
%endif
int_format db "%i", 0
string_format db "%s", 0
reg_format db "Register Dump # %d", NL
db "EAX = %.8X EBX = %.8X ECX = %.8X EDX = %.8X", NL
db "ESI = %.8X EDI = %.8X EBP = %.8X ESP = %.8X", NL
db "EIP = %.8X FLAGS = %.4X %s %s %s %s %s %s %s", NL
db 0
carry_flag db "CF", 0
zero_flag db "ZF", 0
sign_flag db "SF", 0
parity_flag db "PF", 0
overflow_flag db "OF", 0
dir_flag db "DF", 0
aux_carry_flag db "AF", 0
unset_flag db " ", 0
mem_format1 db "Memory Dump # %d Address = %.8X", NL, 0
mem_format2 db "%.8X ", 0
mem_format3 db "%.2X ", 0
stack_format db "Stack Dump # %d", NL
db "EBP = %.8X ESP = %.8X", NL, 0
stack_line_format db "%+4d %.8X %.8X", NL, 0
math_format1 db "Math Coprocessor Dump # %d Control Word = %.4X"
db " Status Word = %.4X", NL, 0
valid_st_format db "ST%d: %.10g", NL, 0
invalid_st_format db "ST%d: Invalid ST", NL, 0
empty_st_format db "ST%d: Empty", NL, 0
;
; code is put in the _TEXT segment
;
%ifdef OBJ_TYPE
segment text public align=1 class=code use32
%else
segment .text
%endif
global read_int, print_int, print_string, read_char
global print_char, print_nl, sub_dump_regs, sub_dump_mem
global sub_dump_math, sub_dump_stack
extern _scanf, _printf, _getchar, _putchar, _fputs
read_int:
enter 4,0
pusha
pushf
lea eax, [ebp-4]
push eax
push dword int_format
call _scanf
pop ecx
pop ecx
popf
popa
mov eax, [ebp-4]
leave
ret
print_int:
enter 0,0
pusha
pushf
push eax
push dword int_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
print_string:
enter 0,0
pusha
pushf
push eax
push dword string_format
call _printf
pop ecx
pop ecx
popf
popa
leave
ret
read_char:
enter 4,0
pusha
pushf
call _getchar
mov [ebp-4], eax
popf
popa
mov eax, [ebp-4]
leave
ret
print_char:
enter 0,0
pusha
pushf
push eax
call _putchar
pop ecx
popf
popa
leave
ret
print_nl:
enter 0,0
pusha
pushf
push dword 10 ; 10 == ASCII code for \n
call _putchar
pop ecx
popf
popa
leave
ret
sub_dump_regs:
enter 4,0
pusha
pushf
mov eax, [esp] ; read FLAGS back off stack
mov [ebp-4], eax ; save flags
;
; show which FLAGS are set
;
test eax, CF_MASK
jz cf_off
mov eax, carry_flag
jmp short push_cf
cf_off:
mov eax, unset_flag
push_cf:
push eax
test dword [ebp-4], PF_MASK
jz pf_off
mov eax, parity_flag
jmp short push_pf
pf_off:
mov eax, unset_flag
push_pf:
push eax
test dword [ebp-4], AF_MASK
jz af_off
mov eax, aux_carry_flag
jmp short push_af
af_off:
mov eax, unset_flag
push_af:
push eax
test dword [ebp-4], ZF_MASK
jz zf_off
mov eax, zero_flag
jmp short push_zf
zf_off:
mov eax, unset_flag
push_zf:
push eax
test dword [ebp-4], SF_MASK
jz sf_off
mov eax, sign_flag
jmp short push_sf
-
Stephen
Re:code not outputting data string
And this is the second part of the file:
sf_off:
mov eax, unset_flag
push_sf:
push eax
test dword [ebp-4], DF_MASK
jz df_off
mov eax, dir_flag
jmp short push_df
df_off:
mov eax, unset_flag
push_df:
push eax
test dword [ebp-4], OF_MASK
jz of_off
mov eax, overflow_flag
jmp short push_of
of_off:
mov eax, unset_flag
push_of:
push eax
push dword [ebp-4] ; FLAGS
mov eax, [ebp+4]
sub eax, 10 ; EIP on stack is 10 bytes ahead of orig
push eax ; EIP
lea eax, [ebp+12]
push eax ; original ESP
push dword [ebp] ; original EBP
push edi
push esi
push edx
push ecx
push ebx
push dword [ebp-8] ; original EAX
push dword [ebp+8] ; # of dump
push dword reg_format
call _printf
add esp, 76
popf
popa
leave
ret 4
sub_dump_stack:
enter 0,0
pusha
pushf
lea eax, [ebp+20]
push eax ; original ESP
push dword [ebp] ; original EBP
push dword [ebp+8] ; # of dump
push dword stack_format
call _printf
add esp, 16
mov ebx, [ebp] ; ebx = original ebp
mov eax, [ebp+16] ; eax = # dwords above ebp
shl eax, 2 ; eax *= 4
add ebx, eax ; ebx = & highest dword in stack to display
mov edx, [ebp+16]
mov ecx, edx
add ecx, [ebp+12]
inc ecx ; ecx = # of dwords to display
stack_line_loop:
push edx
push ecx ; save ecx & edx
push dword [ebx] ; value on stack
push ebx ; address of value on stack
mov eax, edx
sal eax, 2 ; eax = 4*edx
push eax ; offset from ebp
push dword stack_line_format
call _printf
add esp, 16
pop ecx
pop edx
sub ebx, 4
dec edx
loop stack_line_loop
popf
popa
leave
ret 12
sub_dump_mem:
enter 0,0
pusha
pushf
push dword [ebp+12]
push dword [ebp+16]
push dword mem_format1
call _printf
add esp, 12
mov esi, [ebp+12] ; address
and esi, 0FFFFFFF0h ; move to start of paragraph
mov ecx, [ebp+8]
inc ecx
mem_outer_loop:
push ecx
push esi
push dword mem_format2
call _printf
add esp, 8
xor ebx, ebx
mem_hex_loop:
xor eax, eax
mov al, [esi + ebx]
push eax
push dword mem_format3
call _printf
add esp, 8
inc ebx
cmp ebx, 16
jl mem_hex_loop
mov eax, '"'
call print_char
xor ebx, ebx
mem_char_loop:
xor eax, eax
mov al, [esi+ebx]
cmp al, 32
jl non_printable
cmp al, 126
jg non_printable
jmp short mem_char_loop_continue
non_printable:
mov eax, '?'
mem_char_loop_continue:
call print_char
inc ebx
cmp ebx, 16
jl mem_char_loop
mov eax, '"'
call print_char
call print_nl
add esi, 16
pop ecx
loop mem_outer_loop
popf
popa
leave
ret 12
; function sub_dump_math
; prints out state of math coprocessor without modifying the coprocessor
; or regular processor state
; Parameters:
; dump number - dword at [ebp+8]
; Local variables:
; ebp-108 start of fsave buffer
; ebp-116 temp double
; Notes: This procedure uses the Pascal convention.
; fsave buffer structure:
; ebp-108 control word
; ebp-104 status word
; ebp-100 tag word
; ebp-80 ST0
; ebp-70 ST1
; ebp-60 ST2 ...
; ebp-10 ST7
;
sub_dump_math:
enter 116,0
pusha
pushf
fsave [ebp-108] ; save coprocessor state to memory
mov eax, [ebp-104] ; status word
and eax, 0FFFFh
push eax
mov eax, [ebp-108] ; control word
and eax, 0FFFFh
push eax
push dword [ebp+8]
push dword math_format1
call _printf
add esp, 16
;
; rotate tag word so that tags in same order as numbers are
; in the stack
;
mov cx, [ebp-104] ; ax = status word
shr cx, 11
and cx, 7 ; cl = physical state of number on stack top
mov bx, [ebp-100] ; bx = tag word
shl cl,1 ; cl *= 2
ror bx, cl ; move top of stack tag to lowest bits
mov edi, 0 ; edi = stack number of number
lea esi, [ebp-80] ; esi = address of ST0
mov ecx, 8 ; ecx = loop counter
tag_loop:
push ecx
mov ax, 3
and ax, bx ; ax = current tag
or ax, ax ; 00 -> valid number
je valid_st
cmp ax, 1 ; 01 -> zero
je zero_st
cmp ax, 2 ; 10 -> invalid number
je invalid_st
push edi ; 11 -> empty
push dword empty_st_format
call _printf
add esp, 8
jmp short cont_tag_loop
zero_st:
fldz
jmp short print_real
valid_st:
fld tword [esi]
print_real:
fstp qword [ebp-116]
push dword [ebp-112]
push dword [ebp-116]
push edi
push dword valid_st_format
call _printf
add esp, 16
jmp short cont_tag_loop
invalid_st:
push edi
push dword invalid_st_format
call _printf
add esp, 8
cont_tag_loop:
ror bx, 2 ; mov next tag into lowest bits
inc edi
add esi, 10 ; mov to next number on stack
pop ecx
loop tag_loop
frstor [ebp-108] ; restore coprocessor state
popf
popa
leave
ret 4
sf_off:
mov eax, unset_flag
push_sf:
push eax
test dword [ebp-4], DF_MASK
jz df_off
mov eax, dir_flag
jmp short push_df
df_off:
mov eax, unset_flag
push_df:
push eax
test dword [ebp-4], OF_MASK
jz of_off
mov eax, overflow_flag
jmp short push_of
of_off:
mov eax, unset_flag
push_of:
push eax
push dword [ebp-4] ; FLAGS
mov eax, [ebp+4]
sub eax, 10 ; EIP on stack is 10 bytes ahead of orig
push eax ; EIP
lea eax, [ebp+12]
push eax ; original ESP
push dword [ebp] ; original EBP
push edi
push esi
push edx
push ecx
push ebx
push dword [ebp-8] ; original EAX
push dword [ebp+8] ; # of dump
push dword reg_format
call _printf
add esp, 76
popf
popa
leave
ret 4
sub_dump_stack:
enter 0,0
pusha
pushf
lea eax, [ebp+20]
push eax ; original ESP
push dword [ebp] ; original EBP
push dword [ebp+8] ; # of dump
push dword stack_format
call _printf
add esp, 16
mov ebx, [ebp] ; ebx = original ebp
mov eax, [ebp+16] ; eax = # dwords above ebp
shl eax, 2 ; eax *= 4
add ebx, eax ; ebx = & highest dword in stack to display
mov edx, [ebp+16]
mov ecx, edx
add ecx, [ebp+12]
inc ecx ; ecx = # of dwords to display
stack_line_loop:
push edx
push ecx ; save ecx & edx
push dword [ebx] ; value on stack
push ebx ; address of value on stack
mov eax, edx
sal eax, 2 ; eax = 4*edx
push eax ; offset from ebp
push dword stack_line_format
call _printf
add esp, 16
pop ecx
pop edx
sub ebx, 4
dec edx
loop stack_line_loop
popf
popa
leave
ret 12
sub_dump_mem:
enter 0,0
pusha
pushf
push dword [ebp+12]
push dword [ebp+16]
push dword mem_format1
call _printf
add esp, 12
mov esi, [ebp+12] ; address
and esi, 0FFFFFFF0h ; move to start of paragraph
mov ecx, [ebp+8]
inc ecx
mem_outer_loop:
push ecx
push esi
push dword mem_format2
call _printf
add esp, 8
xor ebx, ebx
mem_hex_loop:
xor eax, eax
mov al, [esi + ebx]
push eax
push dword mem_format3
call _printf
add esp, 8
inc ebx
cmp ebx, 16
jl mem_hex_loop
mov eax, '"'
call print_char
xor ebx, ebx
mem_char_loop:
xor eax, eax
mov al, [esi+ebx]
cmp al, 32
jl non_printable
cmp al, 126
jg non_printable
jmp short mem_char_loop_continue
non_printable:
mov eax, '?'
mem_char_loop_continue:
call print_char
inc ebx
cmp ebx, 16
jl mem_char_loop
mov eax, '"'
call print_char
call print_nl
add esi, 16
pop ecx
loop mem_outer_loop
popf
popa
leave
ret 12
; function sub_dump_math
; prints out state of math coprocessor without modifying the coprocessor
; or regular processor state
; Parameters:
; dump number - dword at [ebp+8]
; Local variables:
; ebp-108 start of fsave buffer
; ebp-116 temp double
; Notes: This procedure uses the Pascal convention.
; fsave buffer structure:
; ebp-108 control word
; ebp-104 status word
; ebp-100 tag word
; ebp-80 ST0
; ebp-70 ST1
; ebp-60 ST2 ...
; ebp-10 ST7
;
sub_dump_math:
enter 116,0
pusha
pushf
fsave [ebp-108] ; save coprocessor state to memory
mov eax, [ebp-104] ; status word
and eax, 0FFFFh
push eax
mov eax, [ebp-108] ; control word
and eax, 0FFFFh
push eax
push dword [ebp+8]
push dword math_format1
call _printf
add esp, 16
;
; rotate tag word so that tags in same order as numbers are
; in the stack
;
mov cx, [ebp-104] ; ax = status word
shr cx, 11
and cx, 7 ; cl = physical state of number on stack top
mov bx, [ebp-100] ; bx = tag word
shl cl,1 ; cl *= 2
ror bx, cl ; move top of stack tag to lowest bits
mov edi, 0 ; edi = stack number of number
lea esi, [ebp-80] ; esi = address of ST0
mov ecx, 8 ; ecx = loop counter
tag_loop:
push ecx
mov ax, 3
and ax, bx ; ax = current tag
or ax, ax ; 00 -> valid number
je valid_st
cmp ax, 1 ; 01 -> zero
je zero_st
cmp ax, 2 ; 10 -> invalid number
je invalid_st
push edi ; 11 -> empty
push dword empty_st_format
call _printf
add esp, 8
jmp short cont_tag_loop
zero_st:
fldz
jmp short print_real
valid_st:
fld tword [esi]
print_real:
fstp qword [ebp-116]
push dword [ebp-112]
push dword [ebp-116]
push edi
push dword valid_st_format
call _printf
add esp, 16
jmp short cont_tag_loop
invalid_st:
push edi
push dword invalid_st_format
call _printf
add esp, 8
cont_tag_loop:
ror bx, 2 ; mov next tag into lowest bits
inc edi
add esi, 10 ; mov to next number on stack
pop ecx
loop tag_loop
frstor [ebp-108] ; restore coprocessor state
popf
popa
leave
ret 4