Assembly inside a C++ program

Question

ubuntuubuntu 0 Newbie Poster

15 Years Ago

Hello,
I have a program, let's say foo.cpp . If I do "g++ -S foo.cpp". That generates the file "foo.S" with assembly code. I would like to compare the assembly code foo.S with the assembly code generated if I put foo.S in a c program (even though there should be no difference), but I don't know how to do it. For foo.cpp =

#include <iostream>

using namespace std;
int main() {
  cout << "a47" << endl;
  return 0;
}

for example, I get foo.S =

.mod_init_func
	.align 2
	.long	__GLOBAL__I_main
.lcomm __ZSt8__ioinit,1,0
	.cstring
LC0:
	.ascii "a\0"
	.text
	.align 1,0x90
.globl _main
_main:
LFB1480:
	pushl	%ebp
LCFI0:
	movl	%esp, %ebp
LCFI1:
	pushl	%ebx
LCFI2:
	subl	$20, %esp
LCFI3:
	call	L3
"L00000000001$pb":
L3:
	popl	%ebx
	leal	LC0-"L00000000001$pb"(%ebx), %eax
	movl	%eax, 4(%esp)
	leal	L__ZSt4cout$non_lazy_ptr-"L00000000001$pb"(%ebx), %eax
	movl	(%eax), %eax
	movl	%eax, (%esp)
	call	L__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc$stub
	movl	%eax, %edx
	leal	L__ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_$non_lazy_ptr-"L00000000001$pb"(%ebx), %eax
	movl	(%eax), %eax
	movl	%eax, 4(%esp)
	movl	%edx, (%esp)
	call	L__ZNSolsEPFRSoS_E$stub
	movl	$0, %eax
	addl	$20, %esp
	popl	%ebx
	leave
	ret
LFE1480:
	.align 1,0x90
___tcf_0:
LFB1489:
	pushl	%ebp
LCFI4:
	movl	%esp, %ebp
LCFI5:
	pushl	%ebx
LCFI6:
	subl	$20, %esp
LCFI7:
	call	L6
"L00000000002$pb":
L6:
	popl	%ebx
	leal	__ZSt8__ioinit-"L00000000002$pb"(%ebx), %eax
	movl	%eax, (%esp)
	call	L__ZNSt8ios_base4InitD1Ev$stub
	addl	$20, %esp
	popl	%ebx
	leave
	ret
LFE1489:
	.section __TEXT,__StaticInit,regular,pure_instructions
	.align 1
__Z41__static_initialization_and_destruction_0ii:
LFB1488:
	pushl	%ebp
LCFI8:
	movl	%esp, %ebp
LCFI9:
	pushl	%ebx
LCFI10:
	subl	$36, %esp
LCFI11:
	call	L12
"L00000000003$pb":
L12:
	popl	%ebx
	movl	%eax, -12(%ebp)
	movl	%edx, -16(%ebp)
	cmpl	$65535, -16(%ebp)
	jne	L11
	cmpl	$1, -12(%ebp)
	jne	L11
	leal	__ZSt8__ioinit-"L00000000003$pb"(%ebx), %eax
	movl	%eax, (%esp)
	call	L__ZNSt8ios_base4InitC1Ev$stub
	leal	L___dso_handle$non_lazy_ptr-"L00000000003$pb"(%ebx), %eax
	movl	(%eax), %eax
	movl	%eax, 8(%esp)
	movl	$0, 4(%esp)
	leal	___tcf_0-"L00000000003$pb"(%ebx), %eax
	movl	%eax, (%esp)
	call	L___cxa_atexit$stub
L11:
	addl	$36, %esp
	popl	%ebx
	leave
	ret
LFE1488:
	.align 1
__GLOBAL__I_main:
LFB1490:
	pushl	%ebp
LCFI12:
	movl	%esp, %ebp
LCFI13:
	subl	$8, %esp
LCFI14:
	movl	$65535, %edx
	movl	$1, %eax
	call	__Z41__static_initialization_and_destruction_0ii
	leave
	ret
LFE1490:
	.section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support
EH_frame1:
	.set L$set$0,LECIE1-LSCIE1
	.long L$set$0
LSCIE1:
	.long	0x0
	.byte	0x1
	.ascii "zPR\0"
	.byte	0x1
	.byte	0x7c
	.byte	0x8
	.byte	0x6
	.byte	0x9b
	.long	L___gxx_personality_v0$non_lazy_ptr-.
	.byte	0x10
	.byte	0xc
	.byte	0x5
	.byte	0x4
	.byte	0x88
	.byte	0x1
	.align 2
LECIE1:
	.globl _main.eh
_main.eh:
LSFDE1:
	.set L$set$1,LEFDE1-LASFDE1
	.long L$set$1
LASFDE1:
	.long	LASFDE1-EH_frame1
	.long	LFB1480-.
	.set L$set$2,LFE1480-LFB1480
	.long L$set$2
	.byte	0x0
	.byte	0x4
	.set L$set$3,LCFI0-LFB1480
	.long L$set$3
	.byte	0xe
	.byte	0x8
	.byte	0x84
	.byte	0x2
	.byte	0x4
	.set L$set$4,LCFI1-LCFI0
	.long L$set$4
	.byte	0xd
	.byte	0x4
	.byte	0x4
	.set L$set$5,LCFI3-LCFI1
	.long L$set$5
	.byte	0x83
	.byte	0x3
	.align 2
LEFDE1:
___tcf_0.eh:
LSFDE3:
	.set L$set$6,LEFDE3-LASFDE3
	.long L$set$6
LASFDE3:
	.long	LASFDE3-EH_frame1
	.long	LFB1489-.
	.set L$set$7,LFE1489-LFB1489
	.long L$set$7
	.byte	0x0
	.byte	0x4
	.set L$set$8,LCFI4-LFB1489
	.long L$set$8
	.byte	0xe
	.byte	0x8
	.byte	0x84
	.byte	0x2
	.byte	0x4
	.set L$set$9,LCFI5-LCFI4
	.long L$set$9
	.byte	0xd
	.byte	0x4
	.byte	0x4
	.set L$set$10,LCFI7-LCFI5
	.long L$set$10
	.byte	0x83
	.byte	0x3
	.align 2
LEFDE3:
__Z41__static_initialization_and_destruction_0ii.eh:
LSFDE5:
	.set L$set$11,LEFDE5-LASFDE5
	.long L$set$11
LASFDE5:
	.long	LASFDE5-EH_frame1
	.long	LFB1488-.
	.set L$set$12,LFE1488-LFB1488
	.long L$set$12
	.byte	0x0
	.byte	0x4
	.set L$set$13,LCFI8-LFB1488
	.long L$set$13
	.byte	0xe
	.byte	0x8
	.byte	0x84
	.byte	0x2
	.byte	0x4
	.set L$set$14,LCFI9-LCFI8
	.long L$set$14
	.byte	0xd
	.byte	0x4
	.byte	0x4
	.set L$set$15,LCFI11-LCFI9
	.long L$set$15
	.byte	0x83
	.byte	0x3
	.align 2
LEFDE5:
__GLOBAL__I_main.eh:
LSFDE7:
	.set L$set$16,LEFDE7-LASFDE7
	.long L$set$16
LASFDE7:
	.long	LASFDE7-EH_frame1
	.long	LFB1490-.
	.set L$set$17,LFE1490-LFB1490
	.long L$set$17
	.byte	0x0
	.byte	0x4
	.set L$set$18,LCFI12-LFB1490
	.long L$set$18
	.byte	0xe
	.byte	0x8
	.byte	0x84
	.byte	0x2
	.byte	0x4
	.set L$set$19,LCFI13-LCFI12
	.long L$set$19
	.byte	0xd
	.byte	0x4
	.align 2
LEFDE7:
	.section __IMPORT,__jump_table,symbol_stubs,self_modifying_code+pure_instructions,5
L___cxa_atexit$stub:
	.indirect_symbol ___cxa_atexit
	hlt ; hlt ; hlt ; hlt ; hlt
	.section __IMPORT,__pointers,non_lazy_symbol_pointers
L__ZSt4cout$non_lazy_ptr:
	.indirect_symbol __ZSt4cout
	.long	0
	.section __IMPORT,__jump_table,symbol_stubs,self_modifying_code+pure_instructions,5
L__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc$stub:
	.indirect_symbol __ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
	hlt ; hlt ; hlt ; hlt ; hlt
L__ZNSolsEPFRSoS_E$stub:
	.indirect_symbol __ZNSolsEPFRSoS_E
	hlt ; hlt ; hlt ; hlt ; hlt
	.section __IMPORT,__pointers,non_lazy_symbol_pointers
L__ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_$non_lazy_ptr:
	.indirect_symbol __ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
	.long	0
L___dso_handle$non_lazy_ptr:
	.indirect_symbol ___dso_handle
	.long	0
	.section __IMPORT,__jump_table,symbol_stubs,self_modifying_code+pure_instructions,5
L__ZNSt8ios_base4InitD1Ev$stub:
	.indirect_symbol __ZNSt8ios_base4InitD1Ev
	hlt ; hlt ; hlt ; hlt ; hlt
	.section __IMPORT,__pointers,non_lazy_symbol_pointers
L___gxx_personality_v0$non_lazy_ptr:
	.indirect_symbol ___gxx_personality_v0
	.long	0
	.section __IMPORT,__jump_table,symbol_stubs,self_modifying_code+pure_instructions,5
L__ZNSt8ios_base4InitC1Ev$stub:
	.indirect_symbol __ZNSt8ios_base4InitC1Ev
	hlt ; hlt ; hlt ; hlt ; hlt
	.constructor
	.destructor
	.align 1
	.subsections_via_symbols

I thought this would work, but it doesn't:

asm(" ** ALL THE ASSEMBLY CODE ABOVE ** ");

A friend suggested me to use
perl -pi~ -e ’s/\"/\\\"/g; s/(.*)/\"$1\\\n\"/ig’ foo.s
but it didn't work either.
Does anyone know how to do this? Thank you in advance!

assembly c++

2 Contributors
7 Replies
326 Views
12 Hours Discussion Span
Latest Post 15 Years Ago Latest Post by gerard4143

gerard4143 371 Nearly a Posting Maven

15 Years Ago

Are you using Linux?
If you are, you'd be better off trying object dump of the code like:

objdump -D source.cpp>testfile

Then open testfile in a text editor and inspect it there...Gerard4143

Edited 15 Years Ago by gerard4143 because: n/a

gerard4143 371 Nearly a Posting Maven

15 Years Ago

Are you talking about stripping the functionality(assem code) out of a cpp file and inserting it into another cpp file? I guess what I'm asking is...what are you trying to do?

Edited 15 Years Ago by gerard4143 because: n/a

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ubuntuubuntu 0 Newbie Poster · Answer 1 · 2009-10-13T03:11:31+00:00

That's a good suggestion, but actually what I am supposed to do is this: take a program in C++, transform it in an assembly file and then use the function "asm" to inline it in a C++ program and compare the results. Any guess on how this can be done? Thank you!

ubuntuubuntu 0 Newbie Poster · Answer 2 · 2009-10-13T04:45:31+00:00

What I am trying to do is the following:

- Take a file foo.cpp .
- Compile it with g++ -S -O2 foo.cpp .
- Insert foo.s in another file foo2.cpp, so that when someone else compiles foo2.cpp normaly (g++ foo2.cpp) it benefits from the -O2 optimizations.

Do you think it's possible?

gerard4143 371 Nearly a Posting Maven · Answer 3 · 2009-10-13T05:09:23+00:00

I'm asking because I think I see what your trying to do..I think. You mean compiling a program foo.cpp into assembler code with the optimizing set to -O2 and then copying the assembler code into another file and compiling normally so that the second file will have the -O2 optimizing...

I still have many questions, like what's in the second file? Is it a blank file before you copy over foo.s? If it isn't how do you manage the two entrance points, i.e. you have two functions that are defined as main now....

ubuntuubuntu 0 Newbie Poster · Answer 4 · 2009-10-13T05:36:38+00:00

Yes, it's an empty file before. In other words, my goal is that the program runs with -O2 optimizations even if the user forgets to compile with this parameter, that is, I need to "mask" this assembly file as it was a C file.

( I know that it would be easier to just give the .s file to the user, but I am constrained to hand a .cpp file)

gerard4143 371 Nearly a Posting Maven · Answer 5 · 2009-10-13T06:11:11+00:00

Yes, it's an empty file before. In other words, my goal is that the program runs with -O2 optimizations even if the user forgets to compile with this parameter, that is, I need to "mask" this assembly file as it was a C file.
( I know that it would be easier to just give the .s file to the user, but I am constrained to hand a .cpp file)

The only problem I see is the C++ compiler, it will try to optimize the second file when it compiles it. So I can't see how you can predict the final outcome of this file if you don't control its compiling...