diff --git a/calma/CalmaRead.c b/calma/CalmaRead.c
index 6862ace2..62b2ae77 100644
--- a/calma/CalmaRead.c
+++ b/calma/CalmaRead.c
@@ -459,7 +459,7 @@ calmaParseUnits(void)
  */
 
 void
-CalmaReadError(char *format, ...)
+CalmaReadError(const char *format, ...)
 {
     va_list args;
     OFFTYPE filepos;
diff --git a/calma/calma.h b/calma/calma.h
index d5f6363e..14e8f73b 100644
--- a/calma/calma.h
+++ b/calma/calma.h
@@ -65,7 +65,7 @@ extern bool CalmaWrite(CellDef *rootDef, FILE *f);
 extern void CalmaReadFile(FILETYPE file, char *filename);
 extern void CalmaTechInit(void);
 extern bool CalmaGenerateArray(FILE *f, TileType type, int llx, int lly, int pitch, int cols, int rows);
-extern void CalmaReadError(char *format, ...);
+extern void CalmaReadError(const char *format, ...) ATTR_FORMAT_PRINTF_1;
 
 /* C99 compat */
 extern void calmaDelContacts(void);
diff --git a/cif/CIFrdutils.c b/cif/CIFrdutils.c
index f190a2ac..90e9c3fd 100644
--- a/cif/CIFrdutils.c
+++ b/cif/CIFrdutils.c
@@ -129,7 +129,7 @@ Plane *cifReadPlane;			/* Plane into which to paint material
 
     /* VARARGS1 */
 void
-CIFReadError(char *format, ...)
+CIFReadError(const char *format, ...)
 {
     va_list args;
 
@@ -153,7 +153,7 @@ CIFReadError(char *format, ...)
 
 
 void
-CIFReadWarning(char *format, ...)
+CIFReadWarning(const char *format, ...)
 {
     va_list args;
 
diff --git a/cif/CIFread.h b/cif/CIFread.h
index c5400391..4b61bfa7 100644
--- a/cif/CIFread.h
+++ b/cif/CIFread.h
@@ -188,8 +188,8 @@ extern int CIFEdgeDirection(CIFPath *first, CIFPath *last);
 
 /* Variable argument procedures require complete prototype */
 
-extern void CIFReadError(char *format, ...);
-extern void CIFReadWarning(char *format, ...);
+extern void CIFReadError(const char *format, ...) ATTR_FORMAT_PRINTF_1;
+extern void CIFReadWarning(const char *format, ...) ATTR_FORMAT_PRINTF_1;
 
 /* Variables shared by the CIF-reading modules, see CIFreadutils.c
  * for more details:
diff --git a/drc/DRCtech.c b/drc/DRCtech.c
index 995d166b..1f47b9c1 100644
--- a/drc/DRCtech.c
+++ b/drc/DRCtech.c
@@ -1020,7 +1020,7 @@ DRCTechAddRule(sectionName, argc, argv)
     char *argv[];
 {
     int which, distance, mdist;
-    char *fmt;
+    const char *fmt;
     static const struct
     {
 	const char *rk_keyword;	/* Initial keyword */
diff --git a/ext2sim/ext2sim.c b/ext2sim/ext2sim.c
index 3252bbbb..6ca3dc11 100644
--- a/ext2sim/ext2sim.c
+++ b/ext2sim/ext2sim.c
@@ -1603,7 +1603,7 @@ int simnodeVisit(node, res, cap)
     EFNodeName *nn;
     HierName *hierName;
     bool isGlob;
-    char *fmt;
+    const char *fmt;
     EFAttr *ap;
 
     if (esDevNodesOnly && node->efnode_client == (ClientData) NULL)
diff --git a/ext2spice/ext2hier.c b/ext2spice/ext2hier.c
index 1bf292f0..7f090516 100644
--- a/ext2spice/ext2hier.c
+++ b/ext2spice/ext2hier.c
@@ -1423,7 +1423,7 @@ spcnodeHierVisit(hc, node, res, cap)
     EFNodeName *nn;
     HierName *hierName;
     bool isConnected = FALSE;
-    char *fmt, *nsn;
+    const char *fmt, *nsn;
     EFAttr *ap;
 
     if (node->efnode_client)
diff --git a/ext2spice/ext2spice.c b/ext2spice/ext2spice.c
index 7bd1693c..d7efe11a 100644
--- a/ext2spice/ext2spice.c
+++ b/ext2spice/ext2spice.c
@@ -3669,7 +3669,8 @@ spcnodeVisit(node, res, cap)
     EFNodeName *nn;
     HierName *hierName;
     bool isConnected = FALSE;
-    char *fmt, *nsn;
+    const char *fmt;
+    char *nsn;
     EFAttr *ap;
 
     if (node->efnode_client)
@@ -3731,7 +3732,7 @@ nodeVisitDebug(node, res, cap)
 {
     EFNodeName *nn;
     HierName *hierName;
-    char *fmt, *nsn;
+    char *nsn;
     EFAttr *ap;
 
     hierName = (HierName *) node->efnode_name->efnn_hier;
diff --git a/extflat/EFerr.c b/extflat/EFerr.c
index 280fb9ad..c69d3bf5 100644
--- a/extflat/EFerr.c
+++ b/extflat/EFerr.c
@@ -64,7 +64,7 @@ extern int Tcl_printf();
  */
 
 void
-efReadError(char *fmt, ...)
+efReadError(const char *fmt, ...)
 {
     va_list args;
 
diff --git a/extflat/extflat.h b/extflat/extflat.h
index 5bbf6612..d02830c1 100644
--- a/extflat/extflat.h
+++ b/extflat/extflat.h
@@ -390,7 +390,7 @@ extern int  efHierSrArray();
 extern int  efHierSrUses();
 extern int  efHierVisitDevs();
 extern EFNode *efNodeMerge();
-extern void efReadError();
+extern void efReadError(const char *fmt, ...) ATTR_FORMAT_PRINTF_1;
 extern int  efReadLine();
 extern bool efSymAdd();
 extern bool efSymAddFile();
diff --git a/graphics/grOGL1.c b/graphics/grOGL1.c
index 9540c9d8..4b3b5acd 100644
--- a/graphics/grOGL1.c
+++ b/graphics/grOGL1.c
@@ -267,6 +267,7 @@ GrOGLInit()
 	{
 	    TxError("No suitable visual!\n");
 	    MainExit(1);
+	    ATTR_UNREACHABLE;
 	}
     }
     grXscrn = grVisualInfo->screen;
diff --git a/lef/lefInt.h b/lef/lefInt.h
index 21e2c88b..521867e5 100644
--- a/lef/lefInt.h
+++ b/lef/lefInt.h
@@ -162,8 +162,8 @@ void LefReadLayerSection();
 
 LefMapping *defMakeInverseLayerMap();
 
-void LefError(int, char *, ...);	/* Variable argument procedure requires */
-					/* parameter list.			*/
+/* Variable argument procedure requires parameter list. */
+void LefError(int, const char *, ...) ATTR_FORMAT_PRINTF_2;
 
 /* C99 compat */
 extern void LefRead();
diff --git a/lef/lefRead.c b/lef/lefRead.c
index 9b9d3c45..b0acca12 100644
--- a/lef/lefRead.c
+++ b/lef/lefRead.c
@@ -306,7 +306,7 @@ LefNextToken(f, ignore_eol)
  */
 
 void
-LefError(int type, char *fmt, ...)
+LefError(int type, const char *fmt, ...)
 {
     static int errors = 0, warnings = 0, messages = 0;
     va_list args;
diff --git a/tcltk/tclmagic.c b/tcltk/tclmagic.c
index 57de6176..4363f7e1 100644
--- a/tcltk/tclmagic.c
+++ b/tcltk/tclmagic.c
@@ -1028,7 +1028,7 @@ TxFlush()
 /*--------------------------------------------------------------*/
 
 int
-Tcl_printf(FILE *f, char *fmt, va_list args_in)
+Tcl_printf(FILE *f, const char *fmt, va_list args_in)
 {
     va_list args;
     static char outstr[128] = "puts -nonewline std";
diff --git a/textio/textio.h b/textio/textio.h
index aa3e5fff..b7c6c1c2 100644
--- a/textio/textio.h
+++ b/textio/textio.h
@@ -68,10 +68,10 @@ extern void TxUseMore();
 extern void TxStopMore();
 
 /* printing procedures with variable arguments lists */
-extern void TxError(char *, ...);
-extern void TxErrorV(char *, va_list args);
-extern void TxPrintf(char *, ...);
-extern char *TxPrintString(char *, ...);
+extern void TxError(const char *, ...) ATTR_FORMAT_PRINTF_1;
+extern void TxErrorV(const char *, va_list args);
+extern void TxPrintf(const char *, ...) ATTR_FORMAT_PRINTF_1;
+extern char *TxPrintString(const char *, ...) ATTR_FORMAT_PRINTF_1;
 
 /* input procedures */
 extern char *TxGetLinePrompt();
diff --git a/textio/textioInt.h b/textio/textioInt.h
index 83de8c62..7075a979 100644
--- a/textio/textioInt.h
+++ b/textio/textioInt.h
@@ -52,7 +52,7 @@ extern bool TxGetInputEvent();
 
 /* Routines with variable argument lists */
 
-extern void txFprintfBasic(FILE *, ...);
+extern void txFprintfBasic(FILE *, const char *fmt, ...) ATTR_FORMAT_PRINTF_2;
 
 /* C99 compat */
 void txCommandsInit();
diff --git a/textio/txOutput.c b/textio/txOutput.c
index 7aec132e..2d1ccf02 100644
--- a/textio/txOutput.c
+++ b/textio/txOutput.c
@@ -76,13 +76,11 @@ static bool txPrintFlag = TRUE;
  */
 
 void
-txFprintfBasic(FILE *f, ...)
+txFprintfBasic(FILE *f, const char *fmt, ...)
 {
     va_list args;
-    char *fmt;
 
-    va_start(args, f);
-    fmt = va_arg(args, char *);
+    va_start(args, fmt);
     Vfprintf(f, fmt, args);
     va_end(args);
 }
@@ -110,7 +108,7 @@ txFprintfBasic(FILE *f, ...)
  */
 
 void
-TxPrintf(char *fmt, ...)
+TxPrintf(const char *fmt, ...)
 {
     va_list args;
     FILE *f;
@@ -161,7 +159,7 @@ TxPrintf(char *fmt, ...)
  */
 
 char *
-TxPrintString(char *fmt, ...)
+TxPrintString(const char *fmt, ...)
 {
     va_list args;
     static char *outstr = NULL;
@@ -302,7 +300,7 @@ TxFlush()
  */
 
 void
-TxError(char *fmt, ...) {
+TxError(const char *fmt, ...) {
     va_list args;
     va_start(args, fmt);
     TxErrorV(fmt, args);
@@ -310,7 +308,7 @@ TxError(char *fmt, ...) {
 }
 
 void
-TxErrorV(char *fmt, va_list args)
+TxErrorV(const char *fmt, va_list args)
 {
     FILE *f;
 
@@ -467,7 +465,7 @@ TxStopMore()
 #ifdef	NEED_VFPRINTF
 
 int
-vfprintf(FILR *iop, char *fmt, va_list args_in)
+vfprintf(FILR *iop, const char *fmt, va_list args_in)
 {
     va_list ap;
     int len;
diff --git a/utils/LIBtextio.c b/utils/LIBtextio.c
index e8fc279d..ef42e225 100644
--- a/utils/LIBtextio.c
+++ b/utils/LIBtextio.c
@@ -96,7 +96,7 @@ TxFlush()
  */
 
 void
-TxError(char *fmt, ...)
+TxError(const char *fmt, ...)
 {
     va_list ap;
 
@@ -126,7 +126,7 @@ TxError(char *fmt, ...)
  */
 
 void
-TxPrintf(char *fmt, ...)
+TxPrintf(const char *fmt, ...)
 {
     va_list ap;
 
diff --git a/utils/geometry.c b/utils/geometry.c
index b5b06503..7b4a4924 100644
--- a/utils/geometry.c
+++ b/utils/geometry.c
@@ -403,7 +403,7 @@ GeoNameToPos(name, manhattan, verbose)
 	{"west",	GEO_WEST,		TRUE},
 	{0}
     };
-    char *fmt;
+    const char *fmt;
     const struct pos *pp;
     int pos;
 
diff --git a/utils/magic.h b/utils/magic.h
index 0dcda8e9..77fd57ad 100644
--- a/utils/magic.h
+++ b/utils/magic.h
@@ -168,6 +168,36 @@ extern char AbortMessage[];
     #define PaLockZOpen  PaLockOpen
 #endif
 
+/* ------------ modern compiler support -------------------------------- */
+
+#if defined(__GNUC__) || defined(__clang__)
+ #define ATTR_FORMAT_PRINTF_1 __attribute__((format (printf,1,2)))
+ #define ATTR_FORMAT_PRINTF_2 __attribute__((format (printf,2,3)))
+ #define ATTR_SENTINEL __attribute__ ((sentinel))
+ #define ATTR_UNREACHABLE __builtin_unreachable()
+ #define ATTR_NORETURN __attribute__((noreturn))
+ #define __unused__(x) x __attribute__((unused))
+
+ #define ANALYSER_CSTRING(n) __attribute__((null_terminated_string_arg(n)))
+ #define ANALYSER_FD_ARG(fd) __attribute__((fd_arg(fd)))
+ #define ANALYSER_MALLOC(dealloc, idx) __attribute__((malloc, malloc(dealloc, idx)))
+ #define ANALYSER_NONNULL(n...) __attribute__((nonnull(n)))
+ #define ANALYSER_RETURNS_NONNULL __attribute__((returns_nonnull))
+#else
+ #define ATTR_FORMAT_PRINTF_1 /* */
+ #define ATTR_FORMAT_PRINTF_2 /* */
+ #define ATTR_SENTINEL /* */
+ #define ATTR_UNREACHABLE /* */
+ #define ATTR_NORETURN /* */
+ #define __unused__(x) x
+
+ #define ANALYSER_CSTRING(n) /* */
+ #define ANALYSER_FD_ARG(fd) /* */
+ #define ANALYSER_MALLOC(dealloc, idx) /* */
+ #define ANALYSER_NONNULL(n...) /* */
+ #define ANALYSER_RETURNS_NONNULL /* */
+#endif
+
 /* ---------------- Start of Machine Configuration Section ----------------- */
 
     /* ------- Configuration:  Handle Missing Routines/Definitions ------- */
diff --git a/utils/main.h b/utils/main.h
index 26f4d00d..bb5acc55 100644
--- a/utils/main.h
+++ b/utils/main.h
@@ -92,7 +92,7 @@ extern Transform RootToEditTransform;
 
 /* global procedures */
 
-extern void MainExit(int);	/* a way of exiting that cleans up after itself */
+extern void MainExit(int) ATTR_NORETURN;	/* a way of exiting that cleans up after itself */
 extern void magicMain();
 
 /* C99 compat */
diff --git a/utils/tech.c b/utils/tech.c
index 20fbcbb6..ac470b72 100644
--- a/utils/tech.c
+++ b/utils/tech.c
@@ -856,7 +856,7 @@ TechPrintLine()
 }
 
 void
-TechError(char *fmt, ...)
+TechError(const char *fmt, ...)
 {
     va_list args;
 
diff --git a/utils/tech.h b/utils/tech.h
index e2cd8ff0..c94c0e80 100644
--- a/utils/tech.h
+++ b/utils/tech.h
@@ -51,7 +51,7 @@ extern bool TechOverridesDefault; /* Set TRUE if technology was specified on
 
 /* ----------------- Exported procedures ---------------- */
 
-extern void TechError(char *, ...);
+extern void TechError(const char *, ...) ATTR_FORMAT_PRINTF_1;
 extern void TechAddClient();
 extern void TechAddAlias();