common: cast arguments to character classification functions to unsigned char

We get failures of this type on the cygwin CI machine:

    15:28:20 common.c: In function `bt_common_string_is_printable`:
    15:28:20 common.c:786:16: error: array subscript has type `char` [-Werror=char-subscripts]
    15:28:20   786 |   if (!isprint(*ch) && *ch != '\n' && *ch != '\r' &&
    15:28:20       |                ^~~

This error only pops up on some platforms that have isprint implemented
using a lookup table.  This table is indexed using `*ch`, which is a
char.  And because char is signed on some platforms, gcc warns that this
is dangerous: we could access the array with a negative index, which
would yield unexpected results.

This is on purpose in newlib (the libc used by cygwin, apparently), see
this comment:

  https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=newlib/libc/include/ctype.h;h=a0009af17485acc3d70586a0051269a7a9c350d5;hb=HEAD#l78

The Linux man page for isprint also mentions it:

       The standards require that the argument c for these functions is
       either EOF or a value that is representable in the type unsigned
       char.  If the argument c is of type char, it must be cast to unsigned
       char, as in the following example:

           char c;
           ...
           res = toupper((unsigned char) c);

       This is necessary because char may be the equivalent of signed char,
       in which case a byte where the top bit is set would be sign extended
       when converting to int, yielding a value that is outside the range of
       unsigned char.

Add casts to unsigned char to fix the various instances of this error.

Change-Id: Ice2305490997f595c6f5140a8be2abaa7fd1d8f6
Signed-off-by: Simon Marchi <[email protected]>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/3194
Reviewed-by: Philippe Proulx <[email protected]>
CI-Build: Michael Jeanson <[email protected]>
Tested-by: jenkins <[email protected]>
(cherry picked from commit 994cd34)

Author: simark

src/common/common.c

@@ -783,7 +783,7 @@ bool bt_common_string_is_printable(const char *input)
 	BT_ASSERT_DBG(input);
 
 	for (ch = input; *ch != '\0'; ch++) {
-		if (!isprint(*ch) && *ch != '\n' && *ch != '\r' &&
+		if (!isprint((unsigned char) *ch) && *ch != '\n' && *ch != '\r' &&
 				*ch != '\t' && *ch != '\v') {
 			printable = false;
 			goto end;

src/plugins/ctf/common/metadata/lexer.l

@@ -134,5 +134,5 @@ _Imaginary			setstring(yyextra, yylval, yytext); return CTF_IMAGINARY;
 
 {IDENTIFIER}			BT_LOGT("Got identifier: id=\"%s\"", yytext); setstring(yyextra, yylval, yytext); if (is_type(yyextra, yytext)) return ID_TYPE; else return IDENTIFIER;
 [ \t\r\n]			; /* ignore */
-.				_BT_LOGE_LINENO(yylineno, "Invalid character: char=\"%c\", val=0x%02x", isprint(yytext[0]) ? yytext[0] : '\0', yytext[0]); return CTF_ERROR;
+.				_BT_LOGE_LINENO(yylineno, "Invalid character: char=\"%c\", val=0x%02x", isprint((unsigned char) yytext[0]) ? yytext[0] : '\0', yytext[0]); return CTF_ERROR;
 %%

src/plugins/ctf/fs-sink/translate-trace-ir-to-ctf-ir.c

@@ -154,14 +154,14 @@ bool ist_valid_identifier(const char *name)
 	}
 
 	/* Make sure the name starts with a letter or `_` */
-	if (!isalpha(name[0]) && name[0] != '_') {
+	if (!isalpha((unsigned char) name[0]) && name[0] != '_') {
 		ist_valid = false;
 		goto end;
 	}
 
 	/* Make sure the name only contains letters, digits, and `_` */
 	for (at = name; *at != '\0'; at++) {
-		if (!isalnum(*at) && *at != '_') {
+		if (!isalnum((unsigned char) *at) && *at != '_') {
 			ist_valid = false;
 			goto end;
 		}

src/plugins/text/dmesg/dmesg.c

@@ -773,7 +773,7 @@ bt_message_iterator_class_next_method_status dmesg_msg_iter_next_one(
 
 		/* Ignore empty lines, once trimmed */
 		for (ch = dmesg_msg_iter->linebuf; *ch != '\0'; ch++) {
-			if (!isspace(*ch)) {
+			if (!isspace((unsigned char) *ch)) {
 				only_spaces = false;
 				break;
 			}

src/plugins/text/pretty/print.c

@@ -639,7 +639,7 @@ void print_escape_string(struct pretty_component *pretty, const char *str)
 		}
 
 		/* Standard characters. */
-		if (!iscntrl(str[i])) {
+		if (!iscntrl((unsigned char) str[i])) {
 			bt_common_g_string_append_c(pretty->string, str[i]);
 			continue;
 		}

tests/utils/tap/tap.c

@@ -109,7 +109,7 @@ _gen_result(int ok, const char *func, const char *file, unsigned int line,
 		if(local_test_name) {
 			name_is_digits = 1;
 			for(c = local_test_name; *c != '\0'; c++) {
-				if(!isdigit(*c) && !isspace(*c)) {
+				if(!isdigit((unsigned char) *c) && !isspace((unsigned char) *c)) {
 					name_is_digits = 0;
 					break;
 				}