Hi all,
I used Gem5 to obtain instruction accesses for ARM processor. I used
-marm option to generate code.
arm-linux-gnueabihf-gcc -static -marm fibcall.c
I believe that only 32-bit ARM instructions are generated using this
option. But the result is shown below:
command line: ./build/ARM/gem5.opt --debug-flags=Exec
configs/example/se.py -c tests/test-progs/malardalen/a.out
Global frequency set at 1000000000000 ticks per second
**** REAL SIMULATION ****
info: Entering event queue @ 0. Starting simulation...
0: system.cpu T0 : @fini+15 : mov.w fp, #0 :
IntAlu : D=0x0000000000000000
500: system.cpu T0 : @_start+3 : mov.w lr, #0 :
IntAlu : D=0x0000000000000000
1000: system.cpu T0 : @_start+7 : ldmstm
1000: system.cpu T0 : @_start+7.0 : ldr_uop r1, [sp, #0] :
MemRead : D=0x0000000000000001 A=0xbeffff00
1500: system.cpu T0 : @_start+7.1 : addi_uop sp, sp, #4 :
IntAlu : D=0x00000000beffff04
2000: system.cpu T0 : @_start+9 : mov r2, sp :
IntAlu : D=0x00000000beffff04
2500: system.cpu T0 : @_start+11 : ldmstm
2500: system.cpu T0 : @_start+11.0 : str_uop r2, [sp, #4] :
MemWrite : D=0x00000000beffff04 A=0xbeffff00
3000: system.cpu T0 : @_start+11.1 : subi_uop sp, sp, #4 :
IntAlu : D=0x00000000beffff00
3500: system.cpu T0 : @_start+13 : ldmstm
3500: system.cpu T0 : @_start+13.0 : str_uop r0, [sp, #4] :
MemWrite : D=0x0000000000000000 A=0xbefffefc
4000: system.cpu T0 : @_start+13.1 : subi_uop sp, sp, #4 :
IntAlu : D=0x00000000befffefc
4500: system.cpu T0 : @_start+15 : ldr.w r12, [pc, #16] :
MemRead : D=0x0000000000009039 A=0x88d8
5000: system.cpu T0 : @_start+19 : str.w r12, [sp, #-4]!
5000: system.cpu T0 : @_start+19.0 : str.w r12, [sp, #-4]! :
MemWrite : D=0x0000000000009039 A=0xbefffef8
5500: system.cpu T0 : @_start+19.1 : subi_uop.w sp, sp, #4 :
IntAlu : D=0x00000000befffef8
6000: system.cpu T0 : @_start+23 : ldr r0, [pc, #12] :
MemRead : D=0x0000000000008a4c A=0x88dc
...
We can see that at 2000, _start+9 is used, which is 2 bytes from _start+7.
So I think a 16-bit instruction is used. Why is it so? Why is it not 32-bit?
Besides, does anyone know what _start+7.0 and _start+7.1 mean? Why do I
have two different instructions with the same memory address?
Thanks in advance.
--
Chao Chen, PhD Student
MIST Lab - mistlab.ca
École Polytechnique de Montréal
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