On Fri, Mar 26, 2021 at 11:28 AM Catalin Marinas
[off-list ref] wrote:

On Mon, Mar 22, 2021 at 03:50:50PM -0700, Andrei Vagin wrote:

quoted

diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 758ae984ff97..3c118c5b0893 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h

@@ -90,6 +90,7 @@ struct user_pt_regs {
      __u64           sp;
      __u64           pc;
      __u64           pstate;
+     __u64           orig_x0;
 };

That's a UAPI change, likely to go wrong. For example, a
ptrace(PTRACE_GETREGSET, pid, REGSET_GPR, data) would write past the end
of an old struct user_pt_regs in the debugger.

ptrace(PTRACE_GETREGSET, ...) receives iovec:
ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov)

iov contains a pointer to a buffer and its size and the kernel fills
only the part that fits the buffer.
I think this interface was invented to allow extending structures
without breaking backward compatibility.

--
Catalin

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