libspl/backtrace: dump registers in libunwind backtraces

More useful stuff, especially when trying to follow a disassembly.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Tino Reichardt <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Closes openzfs#16653

lib/libspl/backtrace.c

@@ -65,32 +65,58 @@ libspl_backtrace(int fd)
 	ssize_t ret __attribute__((unused));
 	unw_context_t uc;
 	unw_cursor_t cp;
-	unw_word_t loc;
+	unw_word_t v;
 	char buf[128];
-	size_t n;
+	size_t n, c;
 
-	ret = write(fd, "Call trace:\n", 12);
 	unw_getcontext(&uc);
+
 	unw_init_local(&cp, &uc);
+	ret = write(fd, "Registers:\n", 11);
+	c = 0;
+	for (uint_t regnum = 0; regnum <= UNW_TDEP_LAST_REG; regnum++) {
+		if (unw_get_reg(&cp, regnum, &v) < 0)
+			continue;
+		const char *name = unw_regname(regnum);
+		for (n = 0; name[n] != '\0' && name[n] != '?'; n++) {}
+		if (n == 0) {
+			buf[0] = '?';
+			n = libspl_u64_to_hex_str(regnum, 2,
+			    &buf[1], sizeof (buf)-1) + 1;
+			name = buf;
+		}
+		ret = write(fd, "      ", 5-MIN(n, 3));
+		ret = write(fd, name, n);
+		ret = write(fd, ": 0x", 4);
+		n = libspl_u64_to_hex_str(v, 18, buf, sizeof (buf));
+		ret = write(fd, buf, n);
+		if (!(++c % 3))
+			ret = write(fd, "\n", 1);
+	}
+	if (c % 3)
+		ret = write(fd, "\n", 1);
+
+	unw_init_local(&cp, &uc);
+	ret = write(fd, "Call trace:\n", 12);
 	while (unw_step(&cp) > 0) {
-		unw_get_reg(&cp, UNW_REG_IP, &loc);
+		unw_get_reg(&cp, UNW_REG_IP, &v);
 		ret = write(fd, "  [0x", 5);
-		n = libspl_u64_to_hex_str(loc, 10, buf, sizeof (buf));
+		n = libspl_u64_to_hex_str(v, 18, buf, sizeof (buf));
 		ret = write(fd, buf, n);
 		ret = write(fd, "] ", 2);
-		unw_get_proc_name(&cp, buf, sizeof (buf), &loc);
+		unw_get_proc_name(&cp, buf, sizeof (buf), &v);
 		for (n = 0; n < sizeof (buf) && buf[n] != '\0'; n++) {}
 		ret = write(fd, buf, n);
 		ret = write(fd, "+0x", 3);
-		n = libspl_u64_to_hex_str(loc, 2, buf, sizeof (buf));
+		n = libspl_u64_to_hex_str(v, 2, buf, sizeof (buf));
 		ret = write(fd, buf, n);
 #ifdef HAVE_LIBUNWIND_ELF
 		ret = write(fd, " (in ", 5);
-		unw_get_elf_filename(&cp, buf, sizeof (buf), &loc);
+		unw_get_elf_filename(&cp, buf, sizeof (buf), &v);
 		for (n = 0; n < sizeof (buf) && buf[n] != '\0'; n++) {}
 		ret = write(fd, buf, n);
 		ret = write(fd, " +0x", 4);
-		n = libspl_u64_to_hex_str(loc, 2, buf, sizeof (buf));
+		n = libspl_u64_to_hex_str(v, 2, buf, sizeof (buf));
 		ret = write(fd, buf, n);
 		ret = write(fd, ")", 1);
 #endif