quick SRF question

If I have a multi-call SRF and a user_fctx struct allocated in the
multi_call_memory_ctx, and in the if(SRF_IS_FIRSTCALL()) block while still
in the multi_call_memory_ctx I use PG_GETARG_TEXT_P(n) to get an argument
to my function, and stash the result of this in my user_fctx struct, am I
guaranteed that this pointer will remain valid throughout the remaining
calls to this SRF, or should I instead use PG_GETARG_TEXT_P_COPY(n)?

Here is an example of what I am talking about

typedef struct testfunc_ctx {
text * txt;
} testfunc_ctx;

Datum testfunc(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
testfunc_ctx *userctx;
MemoryContext oldcontext;

if (SRF_IS_FIRSTCALL())
{
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
userctx = palloc(sizeof(testfunc_ctx));
/* XXX does this need to be PG_GETARG_TEXT_P_COPY, or is this ok like this */
userctx->txt = PG_GETARG_TEXT_P(0);
MemoryContextSwitchTo(oldcontext);
funcctx->user_fctx = userctx;
}

funcctx = SRF_PERCALL_SETUP();
userctx = funcctx->user_fctx;
/* do something with userctx->txt */

if (done)
SRF_RETURN_DONE(funcctx);
else
SRF_RETURN_NEXT(funcctx, result);
}

--
The New Testament offers the basis for modern computer coding theory,
in the form of an affirmation of the binary number system.

But let your communication be Yea, yea; nay, nay: for
whatsoever is more than these cometh of evil.
-- Matthew 5:37