Re: [PATCH v3 5/5] linux-user: Add strace for recvfrom()

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Wed, 2024-08-07 at 14:43 +0200, Philippe Mathieu-Daudé wrote:
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  linux-user/strace.c    | 19 +++++++++++++++++++
>  linux-user/strace.list |  2 +-
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/linux-user/strace.c b/linux-user/strace.c
> index 98ef26b917..d76907fdc9 100644
> --- a/linux-user/strace.c
> +++ b/linux-user/strace.c
> @@ -3127,6 +3127,25 @@ print_bind(CPUArchState *cpu_env, const struct
> syscallname *name,
>  }
>  #endif
>  
> +#ifdef TARGET_NR_recvfrom
> +static void
> +print_recvfrom(CPUArchState *cpu_env, const struct syscallname
> *name,
> +               abi_long arg0, abi_long arg1, abi_long arg2,
> +               abi_long arg3, abi_long arg4, abi_long arg5)
> +{
> +    abi_ulong addrlen;
> +
> +    get_user_ualx(addrlen, arg5, 0);
> +
> +    print_syscall_prologue(name);
> +    print_sockfd(arg0, 0);
> +    print_buf_len(arg1, arg2, 0);
> +    print_flags(msg_flags, arg3, 0);
> +    print_sockaddr(arg4, addrlen, 1);
> +    print_syscall_epilogue(name);
> +}
> +#endif
> +
>  #ifdef TARGET_NR_sendto
>  static void
>  print_sendto(CPUArchState *cpu_env, const struct syscallname *name,
> diff --git a/linux-user/strace.list b/linux-user/strace.list
> index 5a86419e7d..77ca824f9c 100644
> --- a/linux-user/strace.list
> +++ b/linux-user/strace.list
> @@ -1135,7 +1135,7 @@
>  { TARGET_NR_recv, "recv" , "%s(%d,%p,%u,%d)", NULL, NULL },
>  #endif
>  #ifdef TARGET_NR_recvfrom
> -{ TARGET_NR_recvfrom, "recvfrom" , NULL, NULL, NULL },
> +{ TARGET_NR_recvfrom, "recvfrom" , NULL, print_recvfrom, NULL },
>  #endif
>  #ifdef TARGET_NR_recvmmsg
>  { TARGET_NR_recvmmsg, "recvmmsg" , NULL, NULL, NULL },

I needed to implement read()/write() tracing and stumbled upon this
series, which overall looks like a good thing to have. I spotted a few
issues though.


I get the following build error:

qemu/linux-user/strace.c:3138:5: error: implicit declaration of
function ‘get_user_ualx’; did you mean ‘get_user_ual’? [-Wimplicit-
function-declaration]
 3138 |     get_user_ualx(addrlen, arg5, 0);
      |     ^~~~~~~~~~~~~
      |     get_user_ual


The following helps:

--- a/linux-user/strace.c
+++ b/linux-user/strace.c
@@ -2666,11 +2666,15 @@ static void print_sockfd(abi_long sockfd, int
last)
 
 #endif
 
-#if defined(TARGET_NR_socketcall)
+#if defined(TARGET_NR_socketcall) || defined(TARGET_NR_recvfrom)
 
 #define get_user_ualx(x, gaddr, idx) \
         get_user_ual(x, (gaddr) + (idx) * sizeof(abi_long))
 
+#endif
+
+#if defined(TARGET_NR_socketcall)
+
 static void do_print_socket(const char *name, abi_long arg1)
 {
     abi_ulong domain, type, protocol;


With this I get the following output, which w.r.t. its shape looks
good:

598730 recvfrom(3,"HTTP/1.1 400 Bad request\15\12Connection:
Cl"...,8192,0,{sa_family=0, sa_data={00, 00, 00, 00, 00, 00, 00, 00,
00, 00, 00, 00, 00, 00}},128) = 0

However: aren't we printing the contents of the buffer before the
syscall returns? Same with sockaddr. This would make the output not
very useful.