On 03/11, Jiri Olsa wrote: > > On Mon, Mar 11, 2024 at 04:06:59PM +0100, Oleg Nesterov wrote: > > I forgot everything about the low-level x86_64 code, but... > > > > On 03/11, Jiri Olsa wrote: > > > > > > #ifdef CONFIG_X86_64 > > > + > > > +asm ( > > > + ".pushsection .rodata\n" > > > + ".global uretprobe_syscall_entry\n" > > > + "uretprobe_syscall_entry:\n" > > > + "push %rax\n" > > > + "mov $462, %rax\n" > > > + "syscall\n" > > > > Hmm... I think you need to save/restore more registers clobbered by > > syscall/entry_SYSCALL_64 ? > > hum, so the call happens on the function call return, so I thought > we should just preserve callee saved registers which seems to be > taken care of by the entry_SYSCALL_64 path.. Yes, but we do not know if the (ret)probed function obeys the C-calling convention, perhaps it is low level asm code or not a C function. > I will double check but I won't insist if you think we do not care. > > > + > > > + regs->ax = ax; > > > > probably not strictly needed, we are going to return ax... > > it needs to be there for the bpf program to read proper return > value from regs OK, I see, thanks. Oleg.
