Hi. First, I hope you are fine and the same for your relatives. With this contribution, I enabled using syscalls:sys_exit_execve and syscalls:sys_exit_execveat as tracepoints on arm64. Indeed, before this contribution, the above tracepoint would not print their information as syscall number was set to -1 by calling forget_syscall(). I tested it by compiling a kernel for arm64 and running it within a VM: # Perf was compiled with linux kernel source. root@vm-arm64:~# perf record -ag -e 'syscalls:sys_exit_execve' -e 'syscalls:sys_enter_execve' & [1] 263 root@vm-arm64:~# ls perf.data share root@vm-arm64:~# fg perf record -ag -e 'syscalls:sys_exit_execve' -e 'syscalls:sys_enter_execve' ^C[ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.061 MB perf.data (2 samples) ] root@vm-arm64:~# perf script bash 264 [000] 66.220187: syscalls:sys_enter_execve: filename: 0xaaab05d9d ... # Below line does not appear without this patch. ls 264 [000] 66.226848: syscalls:sys_exit_execve: 0x0 ... Forgetting the syscall number before starting a new thread was confirmed to be a bug [1]. Particularly, the following architectures do not forget the syscall number before starting a new thread: * arm (32 bits) EABI: start_thread() sets r7 to previous r7 for ELF FDPIC and to 0 for other binfmts [2]. * arm (32 bits) OABI: syscall number is set to -1 if ptrace_report_syscall_entry() failed [3]. * mips: start_thread() does not modify current_thread_info->syscall which is taken directly from v0 [4, 5]. * riscv: start_thread() does not modify a7 [6]. * x86_64: start_thread_common() does not touch orig_ax which seems to contain the syscall number [7]. If you see any way to improve this contribution, feel free to share! Change since: v1: * Remove call to forget_syscall() and store previous syscall number in regs->syscallno unconditionnaly. Francis Laniel (1): arm64: Do not forget syscall when starting a new thread. arch/arm64/include/asm/processor.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Best regards and thank you in advance. --- [1] https://lore.kernel.org/linux-arm-kernel/YoT1iLPEbteRTQGZ@xxxxxxx/ [2] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/arm/include/asm/ processor.h#L52 [3] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/arm/kernel/ ptrace.c#L847 [4] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/mips/kernel/ process.c#L52 [5] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/mips/kernel/ scall64-n64.S#L85 [6] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/riscv/kernel/ process.c#L87 [7] https://elixir.bootlin.com/linux/v5.18-rc6/source/arch/x86/kernel/ process_64.c#L505 -- 2.25.1
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