Re: [PATCH RFCv2 08/18] uprobes/x86: Add uprobe syscall to speed up uprobe

On Tue, Feb 25, 2025 at 5:35 AM Jiri Olsa [off-list ref] wrote:

quoted

In later patches I see nop5 is replaced with a call to
uprobe_trampoline_entry, but which part saves
rdi and other regs?
Compiler doesn't automatically spill/fill around USDT's nop/nop5.
Selftest is doing:
+__naked noinline void uprobe_test(void)
so just lucky ?

if you mean registers that would carry usdt arguments, ebpf programs
access those based on assembler operand string stored in usdt record:

No. I'm talking about all normal registers that trap-style uprobe
preserves, but this nop5->call will scratch.
Instead of void uprobe_test(void)
add some arguments to it, and read them before and after nop5 uprobe.
They must remain the same.