From 00b7bced7f5d5c869e0064245e08dc730ff4b3c9 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Mon, 24 Jan 2022 12:50:15 +0900
Subject: [PATCH] [gamecode] Rework PR_RESET_PARAMS to use PR_SetupParams

PR_SetupParams is new and sets up the parameter pointers so older code
that expects only up to 8 parameter will work with both v6p and Ruamoko
progs without having to check what progs are running. PR_SetupParams is
useful even when Ruamoko progs are expected as it reserves the required
space (respecting alignment) on the stack and returns a pointer to the
top (bottom? confusing) of the stack. PR_PushFrame and PR_PopFrame
need to be used around PR_SetupParams, regardless of using temp strings,
to avoid a stack leak (need to do an audit).
---
 include/QF/progs.h      | 42 +++++++++++++++++++++++++++++++++++------
 libs/gamecode/pr_exec.c | 33 ++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/include/QF/progs.h b/include/QF/progs.h
index 066a479af..78e9913c9 100644
--- a/include/QF/progs.h
+++ b/include/QF/progs.h
@@ -82,15 +82,13 @@ void PR_RunError (progs_t *pr, const char *error, ...) __attribute__((format(PRI
 	\warning Failure to use this macro before assigning to the P_* macros can
 	cause corruption of the VM data due to "register" based calling. Can be
 	safely ignored for parameterless functions, or forwarding parameters
-	though a builtin.
+	though a builtin. However, it is ok (and encouraged) to call
+	PR_SetupParams instead, as this macro calls PR_SetupParams with
+	PR_MAX_PARAMS and 1 for the alignment.
 
 	\hideinitializer
 */
-#define PR_RESET_PARAMS(pr)							\
-	do {											\
-		(pr)->pr_params[0] = (pr)->pr_real_params[0];	\
-		(pr)->pr_params[1] = (pr)->pr_real_params[1];	\
-	} while (0)
+#define PR_RESET_PARAMS(pr)	PR_SetupParams (pr, PR_MAX_PARAMS, 1)
 
 /**	\name Detouring Function Calls
 
@@ -155,6 +153,38 @@ void PR_RestoreParams (progs_t *pr, pr_stashed_params_t *params);
 */
 void PR_PushFrame (progs_t *pr);
 
+/** Reserve space on the data stack and set up the param pointers.
+
+	For v6p progs, this only sets up the param pointers as v6p progs do not
+	have a data stack.
+
+	For Ruamoko progs, space for at least \a num_params (each being 4 words)
+	is created on the stack, with a minimum alignment of min_alignment words,
+	or 4, whichever is larger.
+
+	\param pr		pointer to ::progs_t VM struct
+	\param num_params Number of parameter slots needed for the function call.
+					Each slot is 4 words. dvec4 and lvec4 parameters require
+					8 words and must be 8-word aligned. dvec3 and lvec3
+					also require 8 words due to the minimum 4 word alignment,
+					but have no alignment requirements themselves. Be sure to
+					take this into account in size calculations.
+	\param min_alignment Minimum number of words to which the stack will be
+					aligned. Must be a power of two. Note that when passing
+					dvec4 or lvec4 parameters, they have a hardware-enforced
+					requirement of 8 word alignment. This means that for
+					something like (int, lvec4), there will be an unused
+					parameter slot between the int and the lvec4.
+					Ignored for v6p progs.
+	\return 		Pointer to the base of the created parameter area. For
+					v6p progs, this is just .param_0, but for Ruamoko progs
+					this will be the current top of the the data stack after
+					adjustment for the parameter space.
+	\note Attempting to pass more than PR_MAX_PARAMS parameters to v6p progs
+	is a hard error.
+*/
+pr_type_t *PR_SetupParams (progs_t *pr, int num_params, int min_alignment);
+
 /** Pop an execution frame from the VM stack. Restores execution state. Also
 	frees any temporary strings allocated in this frame (via
 	PR_FreeTempStrings()).
diff --git a/libs/gamecode/pr_exec.c b/libs/gamecode/pr_exec.c
index 19507665c..a78b01f9a 100644
--- a/libs/gamecode/pr_exec.c
+++ b/libs/gamecode/pr_exec.c
@@ -458,6 +458,9 @@ PR_CallFunction (progs_t *pr, pr_func_t fnum, pr_type_t *return_ptr)
 static void
 check_stack_pointer (progs_t *pr, pr_ptr_t stack, int size)
 {
+	if (stack & 3) {
+		PR_RunError (pr, "Progs stack not aligned");
+	}
 	if (stack < pr->stack_bottom) {
 		PR_RunError (pr, "Progs stack overflow");
 	}
@@ -466,6 +469,36 @@ check_stack_pointer (progs_t *pr, pr_ptr_t stack, int size)
 	}
 }
 
+VISIBLE pr_type_t *
+PR_SetupParams (progs_t *pr, int num_params, int min_alignment)
+{
+	if (pr->progs->version < PROG_VERSION) {
+		if (num_params > PR_MAX_PARAMS) {
+			PR_Error (pr, "attempt to settup more than %d params",
+					  PR_MAX_PARAMS);
+		}
+		pr->pr_params[0] = pr->pr_real_params[0];
+		pr->pr_params[1] = pr->pr_real_params[1];
+		return pr->pr_real_params[0];
+	}
+	int         offset = num_params * 4;
+	if (min_alignment < 4) {
+		min_alignment = 4;
+	}
+	pr_ptr_t    mask = ~(min_alignment - 1);
+	pr_ptr_t    stack = (*pr->globals.stack - offset) & mask;
+	if (pr_boundscheck->int_val) {
+		check_stack_pointer (pr, stack, 0);
+	}
+	*pr->globals.stack = stack;
+	pr->pr_params[0] = pr->pr_globals + stack;
+	num_params = min (num_params, PR_MAX_PARAMS);
+	for (int i = 1; i < num_params; i++) {
+		pr->pr_params[i] = pr->pr_params[0] + i * 4;
+	}
+	return pr->pr_params[0];
+}
+
 static inline void
 pr_memset (pr_type_t *dst, int val, pr_uint_t count)
 {