Re: [PATCH] gdbstub: add support to Xfer:auxv:read: packet

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/7/20 1:04 AM, Lirong Yuan wrote:
> This allows gdb to access the target’s auxiliary vector,
> which can be helpful for telling system libraries important details
> about the hardware, operating system, and process.
> 
> Signed-off-by: Lirong Yuan <yuanzi@google.com>
> ---
>   gdbstub.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 50 insertions(+)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index 22a2d630cd..c2865ea873 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -2105,6 +2105,12 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx)
>           pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf),
>                   ";qXfer:features:read+");
>       }
> +#ifdef CONFIG_USER_ONLY
> +    if (gdb_ctx->s->c_cpu->opaque) {
> +        pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf),
> +                ";qXfer:auxv:read+");
> +    }
> +#endif
>   
>       if (gdb_ctx->num_params &&
>           strstr(gdb_ctx->params[0].data, "multiprocess+")) {
> @@ -2166,6 +2172,42 @@ static void handle_query_xfer_features(GdbCmdContext *gdb_ctx, void *user_ctx)
>       put_packet_binary(gdb_ctx->s, gdb_ctx->str_buf, len + 1, true);
>   }
>   
> +#ifdef CONFIG_USER_ONLY
> +static void handle_query_xfer_auxv(GdbCmdContext *gdb_ctx, void *user_ctx)
> +{
> +    TaskState *ts;
> +    unsigned long offset, len, saved_auxv, auxv_len;
> +    const char *mem;
> +
> +    if (gdb_ctx->num_params < 2) {
> +        put_packet(gdb_ctx->s, "E22");
> +        return;
> +    }
> +
> +    offset = gdb_ctx->params[0].val_ul;
> +    len = gdb_ctx->params[1].val_ul;
> +
> +    ts = gdb_ctx->s->c_cpu->opaque;
> +    saved_auxv = ts->info->saved_auxv;
> +    auxv_len = ts->info->auxv_len;

Maybe check we are in range first?

        if (offset + len > auxv_len) {
            put_packet(gdb_ctx->s, "E22");
            return;
        }

> +    mem = (const char *)(saved_auxv + offset);
> +
> +    if (len > (MAX_PACKET_LENGTH - 5) / 2) {
> +        len = (MAX_PACKET_LENGTH - 5) / 2;
> +    }
> +
> +    if (len < auxv_len - offset) {
> +        gdb_ctx->str_buf[0] = 'm';
> +        len = memtox(gdb_ctx->str_buf + 1, mem, len);
> +    } else {
> +        gdb_ctx->str_buf[0] = 'l';
> +        len = memtox(gdb_ctx->str_buf + 1, mem, auxv_len - offset);
> +    }
> +
> +    put_packet_binary(gdb_ctx->s, gdb_ctx->str_buf, len + 1, true);
> +}
> +#endif
> +
>   static void handle_query_attached(GdbCmdContext *gdb_ctx, void *user_ctx)
>   {
>       put_packet(gdb_ctx->s, GDB_ATTACHED);
> @@ -2271,6 +2313,14 @@ static GdbCmdParseEntry gdb_gen_query_table[] = {
>           .cmd_startswith = 1,
>           .schema = "s:l,l0"
>       },
> +#ifdef CONFIG_USER_ONLY
> +    {
> +        .handler = handle_query_xfer_auxv,
> +        .cmd = "Xfer:auxv:read:",
> +        .cmd_startswith = 1,
> +        .schema = "l,l0"
> +    },
> +#endif
>       {
>           .handler = handle_query_attached,
>           .cmd = "Attached:",
>