Re: [PATCH 0/6] updates for linux v5.3

[Rich Felker <dalias@libc.org>]

On Sun, Nov 10, 2019 at 02:08:02AM +0100, Szabolcs Nagy wrote:
> >From 560fd1ebe616fd59c0abcaf86bec6109bfcd2141 Mon Sep 17 00:00:00 2001
> From: Szabolcs Nagy <nsz@port70.net>
> Date: Sun, 3 Nov 2019 22:45:05 +0000
> Subject: [PATCH 4/6] sys/ptrace.h: add PTRACE_GET_SYSCALL_INFO from linux v5.3
> 
> ptrace API to get details of the syscall the tracee is blocked in, see
> 
>   linux commit 201766a20e30f982ccfe36bebfad9602c3ff574a
>   ptrace: add PTRACE_GET_SYSCALL_INFO request
> 
> the align attribute was used to keep the layout the same across targets
> e.g. on m68k uint32_t is 2 byte aligned, this helps with compat ptrace.

Can you explain the motivation for this? At first I thought it was for
overall alignment of the structure, but there are also 64-bit members
that aren't aligned, so presumably this is only to get padding after
the initial uint8_t? If so, just add 3 explicit padding members:

> ---
>  include/sys/ptrace.h | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/include/sys/ptrace.h b/include/sys/ptrace.h
> index 229e1f3d..2a868093 100644
> --- a/include/sys/ptrace.h
> +++ b/include/sys/ptrace.h
> @@ -41,6 +41,7 @@ extern "C" {
>  #define PTRACE_SETSIGMASK 0x420b
>  #define PTRACE_SECCOMP_GET_FILTER 0x420c
>  #define PTRACE_SECCOMP_GET_METADATA 0x420d
> +#define PTRACE_GET_SYSCALL_INFO 0x420e
>  
>  #define PT_READ_I PTRACE_PEEKTEXT
>  #define PT_READ_D PTRACE_PEEKDATA
> @@ -88,6 +89,11 @@ extern "C" {
>  
>  #define PTRACE_PEEKSIGINFO_SHARED 1
>  
> +#define PTRACE_SYSCALL_INFO_NONE 0
> +#define PTRACE_SYSCALL_INFO_ENTRY 1
> +#define PTRACE_SYSCALL_INFO_EXIT 2
> +#define PTRACE_SYSCALL_INFO_SECCOMP 3
> +
>  #include <bits/ptrace.h>
>  
>  struct __ptrace_peeksiginfo_args {
> @@ -101,6 +107,28 @@ struct __ptrace_seccomp_metadata {
>  	uint64_t flags;
>  };
>  
> +struct __ptrace_syscall_info {
> +	uint8_t op;

Like uint8_t op, __pad[3];

> +	uint32_t arch __attribute__((__aligned__(4)));
> +	uint64_t instruction_pointer;
> +	uint64_t stack_pointer;
> +	union {
> +		struct {
> +			uint64_t nr;
> +			uint64_t args[6];
> +		} entry;
> +		struct {
> +			int64_t rval;
> +			uint8_t is_error;
> +		} exit;
> +		struct {
> +			uint64_t nr;
> +			uint64_t args[6];
> +			uint32_t ret_data;
> +		} seccomp;
> +	};
> +};
> +
>  long ptrace(int, ...);

Otherwise, the API having reserved-namespace struct names is ugly but
it seems this is nothing new...

Rich