11.7.3. gem5 syscall emulation mode syscall tracing
Since gem5 has to implement syscalls itself in syscall emulation mode, it can of course clearly see which syscalls are being made, and we can log them for debug purposes with gem5 tracing, e.g.:
./run \ --emulator gem5 \ --userland userland/arch/x86_64/freestanding/linux/hello.S \ --trace-stdout \ --trace ExecAll,SyscallBase,SyscallVerbose \ ;
the trace as of f2eeceb1cde13a5ff740727526bf916b356cee38 + 1 contains:
0: system.cpu A0 T0 : @asm_main_after_prologue : mov rdi, 0x1
0: system.cpu A0 T0 : @asm_main_after_prologue.0 : MOV_R_I : limm rax, 0x1 : IntAlu : D=0x0000000000000001 flags=(IsInteger|IsMicroop|IsLastMicroop|IsFirstMicroop)
1000: system.cpu A0 T0 : @asm_main_after_prologue+7 : mov rdi, 0x1
1000: system.cpu A0 T0 : @asm_main_after_prologue+7.0 : MOV_R_I : limm rdi, 0x1 : IntAlu : D=0x0000000000000001 flags=(IsInteger|IsMicroop|IsLastMicroop|IsFirstMicroop)
2000: system.cpu A0 T0 : @asm_main_after_prologue+14 : lea rsi, DS:[rip + 0x19]
2000: system.cpu A0 T0 : @asm_main_after_prologue+14.0 : LEA_R_P : rdip t7, %ctrl153, : IntAlu : D=0x000000000040008d flags=(IsInteger|IsMicroop|IsDelayedCommit|IsFirstMicroop)
2500: system.cpu A0 T0 : @asm_main_after_prologue+14.1 : LEA_R_P : lea rsi, DS:[t7 + 0x19] : IntAlu : D=0x00000000004000a6 flags=(IsInteger|IsMicroop|IsLastMicroop)
3500: system.cpu A0 T0 : @asm_main_after_prologue+21 : mov rdi, 0x6
3500: system.cpu A0 T0 : @asm_main_after_prologue+21.0 : MOV_R_I : limm rdx, 0x6 : IntAlu : D=0x0000000000000006 flags=(IsInteger|IsMicroop|IsLastMicroop|IsFirstMicroop)
4000: system.cpu: T0 : syscall write called w/arguments 1, 4194470, 6, 0, 0, 0
hello
4000: system.cpu: T0 : syscall write returns 6
4000: system.cpu A0 T0 : @asm_main_after_prologue+28 : syscall eax : IntAlu : flags=(IsInteger|IsSerializeAfter|IsNonSpeculative|IsSyscall)
5000: system.cpu A0 T0 : @asm_main_after_prologue+30 : mov rdi, 0x3c
5000: system.cpu A0 T0 : @asm_main_after_prologue+30.0 : MOV_R_I : limm rax, 0x3c : IntAlu : D=0x000000000000003c flags=(IsInteger|IsMicroop|IsLastMicroop|IsFirstMicroop)
6000: system.cpu A0 T0 : @asm_main_after_prologue+37 : mov rdi, 0
6000: system.cpu A0 T0 : @asm_main_after_prologue+37.0 : MOV_R_I : limm rdi, 0 : IntAlu : D=0x0000000000000000 flags=(IsInteger|IsMicroop|IsLastMicroop|IsFirstMicroop)
6500: system.cpu: T0 : syscall exit called w/arguments 0, 4194470, 6, 0, 0, 0
6500: system.cpu: T0 : syscall exit returns 0
6500: system.cpu A0 T0 : @asm_main_after_prologue+44 : syscall eax : IntAlu : flags=(IsInteger|IsSerializeAfter|IsNonSpeculative|IsSyscall)
so we see that two syscall lines were added for each syscall, showing the syscall inputs and exit status, just like a mini strace!