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Transcript of Al2ed chapter17
High-Level Language Interface
Chapter 17
S. Dandamudi
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 2
Outline
• Why program in mixed-mode? Focus on C and assembly
• Overview of compiling mixed-mode programs
• Calling assembly procedures from C Parameter passing Returning values Preserving registers Globals and externals
• Illustrative examples
• Calling C functions from assembly
• Inline assembly code AT&T syntax Simple inline statements Extended inline statements Inline examples
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 3
Why Program in Mixed-Mode?
• Pros and cons of assembly language programming Advantages:
» Access to hardware
» Time-efficiency
» Space-efficiency
Problems:» Low productivity
» High maintenance cost
» Lack of portability
• As a result, some programs are written in mixed-modem (e.g., system software)
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 4
Compiling Mixed-Mode Programs
• We use C and assembly mixed-mode programming
• Our emphasis is on the principles• Can be generalized to any type of mixed-mode
programming• To compile
nasm –f elf sample2.asm» Creates sample2.o
gcc –o sample1.out sample1.c sample2.o» Creates sample1.out executable file
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 5
Compiling Mixed-Mode Programs
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 6
Calling Assembly Procedures from C
Parameter Passing• Stack is used for parameter passing• Two ways of pushing arguments onto the stack
Left-to-right» Most languages including Basic, Fortran, Pascal use this
method
» These languages are called left-pusher languages
Right-to-left» C uses this method
» These languages are called right-pusher languages
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 7
Calling Assembly Procedures from C (cont’d)
Example:
sum(a,b,c,d)
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 8
Calling Assembly Procedures from C (cont’d)
Returning Values• Registers are used to return values
Return value type Register used
8-, 16-, 32-bit value EAX
64-bit value EDX:EAX
• Floating-point values are discussed in the next chapter
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 9
Calling Assembly Procedures from C (cont’d)
Preserving Registers• The following registers must be preserved
EBP, EBX, ESI, and EDI• Other registers
If needed, should be preserved by the calling function
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 10
Calling Assembly Procedures from C (cont’d)
Globals and Externals• Mixed-mode programming involves at least two
program modules» One C module and one assembly module
• We have to declare those functions and procedures that are not defined in the same module as external
» See Section 5.10
• Those procedures that are accessed by another modules as global
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 11
Illustrative Examples
• Example 1 hll_ex1c.c hll_test.asm
• Example 2 hll_minmaxc.c hll_minmaxa.asm
• Example 3 hll_arraysumc.c hll_arraysuma.asm
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 12
Calling C Functions from Assembly
• Stack is used to pass parameters (as in our previous discussion) Similar mechanism is used to pass parameters and to
return values
• Since C makes the calling procedure responsible for clearing the stack of the parameters, make sure to clear the parameters after the call instruction as in
add ESP,4
on line 31 in the example program on page 494
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 13
Inline Assembly
• Assembly language statements are embedded into the C code
» Separate assembly module is not necessary
• Assembly statements are identified by placing the keyword asm
• We can use ( ) to compound several assembly statements
asm( assembly statement
assembly statement . . . );
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 14
Inline Assembly (cont’d)
• AT&T Syntax GCC uses this syntax Register naming
» Prefix with % as in %eax
Source and destination order» Reversed
mov eax,ebx
is written as
movl %ebx,%eax
Operand size» Explicit using b, w, l for byte, word, and longword operands
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 15
Inline Assembly (cont’d)
• AT&T Syntax (cont’d) Immediate and constant operands
» Prefix the operands with $movb $255,%almovl $0xFFFFFFFF,%eax
Addressing» Use ( ) rather then [ ]
mov eax,[ebx] is written as
movl (%ebx),%eax» Full protected-mode addressing format
imm32(base,index,scale)Computed as imm32 + base + index*scale
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 16
Inline Assembly (cont’d)
Simple Inline Statementsasm(”incl %eax”);
• Multiple statementsasm(”pushl %eax”);
asm(”incl %eax”);
asm(”popl %eax”); Can be Written as
asm(”pushl %eax; incl %eax; popl %eax”); Or as (to add structure)
asm(”pushl %eax”;
”incl %eax”;
”popl %eax”);
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 17
Inline Assembly (cont’d)
Extended Inline Statements• Format
asm(assembly code
:outputs
:inputs
:clobber list);
• Assembly code Add keyword volatile after asm
» if no compiler optimizations are needed
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 18
Inline Assembly (cont’d)
• Outputs» Format
”=op-constraint” (C-expression)» Example
”=r”(sum)» Output constraints
r = register
m = memory
i = immediate
rm = register or memory,
ri = register or immediate
g = general
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 19
Inline Assembly (cont’d)
• Register lettersLetter Register set
a EAX register
b EBX register
c ECX register
d EDX register
S ESI register
D EDI register
r Any of the 8 general registers
(EAX, EBX, ECX, EDX, ESI, EDI, EBP, ESP)
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 20
Inline Assembly (cont’d)
• Register lettersLetter Register set
q Any of four data registers
(EAX, EBX, ECX, EDX)
A A 64-bit value in EAX and EDX
f Floating-point registers
t Top floating-point register
u Second top floating-point register
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 21
Inline Assembly (cont’d)
• Inputs Similar to how the outputs are specified
(with no = sign) Operands specified in the output and input parts are
assigned sequence numbers 0, 1, 2, …» Can be a total of 10 operands
Exampleasm(“movl %1,%0” :”=r” (sum) /* output */ :”r” (number1) /* input */ );
%0 refers to sum %1 to number1
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 22
Inline Assembly (cont’d)
• Clobber list List of registers modified by the assembly code Lets gcc know of this Example
asm(“movl %0,%%eax”
: /*no output */
:”r” (number1) /* inputs */
:”%eax” /* clobber list */
);
2005
To be used with S. Dandamudi, “Introduction to Assembly Language Programming,” Second Edition, Springer, 2005.
S. Dandamudi Chapter 17: Page 23
Inline Assembly (cont’d)
• Inline examples Example 1
» hll_ex1_inline.c
Example 2» Array sum example» hll_arraysum_inline.c
Example 3» Second version of the last example» hll_arraysum_inline2.c
Last slide