cpumodel

ffmasm examples - cpumodel

This is an example of ffmasm to obtain CPU model from CPUID instruction in AMD64.

Requirements

• Java 22
• AMD64 Linux or Windows
• Maven

How to run

1. Install ffmasm

$ mvn clean install

2. Build cpumodel

$ cd examples/cpumodel
$ mvn clean package

3. Run via Maven

$ mvn exec:java

Press enter to exit.

4. [EXTRA] check assembly in GDB

Run GDB if you want to check assembled code.

You can see PID and address of CodeSegment on the console when you run mvn exec:exec in below.

PID: 928
Addr: 0x7f4c42704000
Intel(R) Core(TM) i3-8145U CPU @ 2.10GHz

Attach to JVM process (928 in this case), and run disas on GDB.

$ gdb -p 928

  :

(gdb) disas 0x7f4c42704000, 0x7f4c42704020
Dump of assembler code from 0x7f4c42704000 to 0x7f4c42704020:
   0x00007f4c42704000:  push   %rbp
   0x00007f4c42704001:  mov    %rsp,%rbp
   0x00007f4c42704004:  push   %rbx
   0x00007f4c42704005:  mov    %rdi,%rax
   0x00007f4c42704008:  mov    %rsi,%r11
   0x00007f4c4270400b:  cpuid
   0x00007f4c4270400d:  mov    %eax,(%r11)
   0x00007f4c42704010:  mov    %ebx,0x4(%r11)
   0x00007f4c42704014:  mov    %ecx,0x8(%r11)
   0x00007f4c42704018:  mov    %edx,0xc(%r11)
   0x00007f4c4270401c:  pop    %rbx
   0x00007f4c4270401e:  leave
   0x00007f4c4270401f:  ret
End of assembler dump.

Calling convention

Calling convention is different between Linux AMD64 and Windows x64. Linux AMD64 conform to System V Application Binary Interface, on the other hand Windows conform to here. You have to conform to them when you assemble.

Expected assembly code in this example on Linux

# prologue
push %rbp
mov  %rsp, %rbp

# Evacuate callee-saved register
push %rbx

# Copy arguments to temporary registers
mov %rdi,%rax
mov %rsi,%r11

# Call CPUID
cpuid

# Store result to given memory
mov %eax,   (%r11)
mov %ebx,  4(%r11)
mov %ecx,  8(%r11)
mov %edx, 12(%r11)

# Restore callee-saved register
pop %rbx

# Epilogue
leave
ret