-Wmacro-shift warns about shifting macro arguments too far (#741)

Fixes #735

include/asm/warning.h

@@ -23,6 +23,7 @@ enum WarningID {
 	WARNING_EMPTY_STRRPL,	      /* Empty second argument in `STRRPL` */
 	WARNING_LARGE_CONSTANT,	      /* Constants too large */
 	WARNING_LONG_STR,	      /* String too long for internal buffers */
+	WARNING_MACRO_SHIFT,	      /* Shift past available arguments in macro */
 	WARNING_NESTED_COMMENT,	      /* Comment-start delimiter in a block comment */
 	WARNING_OBSOLETE,	      /* Obsolete things */
 	WARNING_SHIFT,		      /* Shifting undefined behavior */

src/asm/macro.c

@@ -168,12 +168,17 @@ void macro_ShiftCurrentArgs(int32_t count)
 {
 	if (!macroArgs) {
 		error("Cannot shift macro arguments outside of a macro\n");
-	} else if (macroArgs->shift < macroArgs->nbArgs) {
-		macroArgs->shift += count;
-		if (macroArgs->shift > macroArgs->nbArgs)
+	} else if (count > 0 && (count > macroArgs->nbArgs
+		   || macroArgs->shift > macroArgs->nbArgs - count)) {
+		warning(WARNING_MACRO_SHIFT,
+			"Cannot shift macro arguments past their end\n");
 		macroArgs->shift = macroArgs->nbArgs;
-		else if (macroArgs->shift < 0)
+	} else if (count < 0 && macroArgs->shift < -count) {
+		warning(WARNING_MACRO_SHIFT,
+			"Cannot shift macro arguments past their beginning\n");
 		macroArgs->shift = 0;
+	} else {
+		macroArgs->shift += count;
 	}
 }
 

src/asm/rgbasm.1

@@ -229,6 +229,10 @@ This warning is enabled by
 Warn when a string too long to fit in internal buffers is encountered.
 This warning is enabled by
 .Fl Wall .
+.It Fl Wmacro-shift
+Warn when shifting macro arguments past their limits.
+This warning is enabled by
+.Fl Wextra .
 .It Fl Wno-obsolete
 Warn when obsolete constructs such as the
 .Ic _PI

src/asm/warning.c

@@ -38,6 +38,7 @@ static enum WarningState const defaultWarnings[NB_WARNINGS] = {
 	[WARNING_EMPTY_STRRPL]		= WARNING_DISABLED,
 	[WARNING_LARGE_CONSTANT]	= WARNING_DISABLED,
 	[WARNING_LONG_STR]		= WARNING_DISABLED,
+	[WARNING_MACRO_SHIFT]		= WARNING_DISABLED,
 	[WARNING_NESTED_COMMENT]	= WARNING_ENABLED,
 	[WARNING_OBSOLETE]		= WARNING_ENABLED,
 	[WARNING_SHIFT]			= WARNING_DISABLED,
@@ -79,6 +80,7 @@ static char const *warningFlags[NB_WARNINGS_ALL] = {
 	"empty-strrpl",
 	"large-constant",
 	"long-string",
+	"macro-shift",
 	"nested-comment",
 	"obsolete",
 	"shift",
@@ -110,6 +112,7 @@ static uint8_t const _wallCommands[] = {
 /* Warnings that are less likely to indicate an error */
 static uint8_t const _wextraCommands[] = {
 	WARNING_EMPTY_ENTRY,
+	WARNING_MACRO_SHIFT,
 	WARNING_NESTED_COMMENT,
 	META_WARNING_DONE
 };
@@ -123,6 +126,7 @@ static uint8_t const _weverythingCommands[] = {
 	WARNING_EMPTY_STRRPL,
 	WARNING_LARGE_CONSTANT,
 	WARNING_LONG_STR,
+	WARNING_MACRO_SHIFT,
 	WARNING_NESTED_COMMENT,
 	WARNING_OBSOLETE,
 	WARNING_SHIFT,

test/asm/narg-decreases-after-shift.err

@@ -0,0 +1,2 @@
+warning: narg-decreases-after-shift.asm(14) -> narg-decreases-after-shift.asm::testing(9): [-Wmacro-shift]
+    Cannot shift macro arguments past their end

test/asm/rept-shift.asm

@@ -8,9 +8,7 @@ m: macro
 	; Shifting a little more to check that over-shifting doesn't crash
 	SHIFT
 	SHIFT
-	REPT 256
-		SHIFT
-	ENDR
+	SHIFT 256
 	PRINTLN "\1"
 endm
 

test/asm/rept-shift.err

@@ -1,2 +1,6 @@
-FATAL: rept-shift.asm(17) -> rept-shift.asm::m(14):
+warning: rept-shift.asm(15) -> rept-shift.asm::m(10): [-Wmacro-shift]
+    Cannot shift macro arguments past their end
+warning: rept-shift.asm(15) -> rept-shift.asm::m(11): [-Wmacro-shift]
+    Cannot shift macro arguments past their end
+FATAL: rept-shift.asm(15) -> rept-shift.asm::m(12):
     Macro argument '\1' not defined

test/asm/shift-negative.asm

@@ -12,5 +12,9 @@ ENDM
 m: MACRO
 	shift 2
 	shift -3
+	shift 1
+	shift 1
+	shift -1
+	shift -1
 ENDM
-	m
+	m one

test/asm/shift-negative.err

@@ -0,0 +1,8 @@
+warning: shift-negative.asm(20) -> shift-negative.asm::m(13): [-Wmacro-shift]
+    Cannot shift macro arguments past their end
+warning: shift-negative.asm(20) -> shift-negative.asm::m(14): [-Wmacro-shift]
+    Cannot shift macro arguments past their beginning
+warning: shift-negative.asm(20) -> shift-negative.asm::m(16): [-Wmacro-shift]
+    Cannot shift macro arguments past their end
+warning: shift-negative.asm(20) -> shift-negative.asm::m(18): [-Wmacro-shift]
+    Cannot shift macro arguments past their beginning