set up a UB handler thanks to zig

activated in debug and safe release modes.

build.zig

@@ -4,10 +4,16 @@ pub fn build(b: *std.build.Builder) void {
     const target = b.standardTargetOptions(.{});
     const mode = b.standardReleaseOptions();
 
+    const libsegfault = b.addStaticLibrary("segfault", "src/segfault.zig");
+    libsegfault.setTarget(target);
+    libsegfault.setBuildMode(mode);
+    libsegfault.force_pic = true;
+
     const exe = b.addExecutable("st", null);
     exe.setTarget(target);
     exe.setBuildMode(mode);
     exe.install();
+    exe.linkLibrary(libsegfault);
     exe.linkSystemLibrary("fontconfig");
     exe.linkSystemLibrary("freetype2");
     exe.linkSystemLibrary("Xft");

src/segfault.zig

@@ -0,0 +1,8 @@
+const std = @import("std");
+
+/// installs a segfault handler on supported platforms in debug and safe modes.
+/// while a zig main does this automatically, a C main will want to call this explicitly.
+/// hence, the export for C call convention.
+export fn setupSegfaultHandler() void {
+    std.debug.maybeEnableSegfaultHandler();
+}

x.c

@@ -61,6 +61,8 @@ static void zoomabs(const Arg *);
 static void zoomreset(const Arg *);
 static void ttysend(const Arg *);
 
+extern void setupSegfaultHandler(void);
+
 /* config.h for applying patches and the configuration. */
 #include "config.h"
 
@@ -2103,6 +2105,9 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
+	// install zig's UB handler.
+	setupSegfaultHandler();
+
 	xw.l = xw.t = 0;
 	xw.isfixed = False;
 	xsetcursor(cursorshape);