On 09/08/2016 08:19 PM, Martin Sebor wrote:
While working on the -Wformat-length pass I noticed that in some
diagnostics that make use of the %qc and %qs directives GCC prints
non-printable characters raw.  For example, it might print a newline,
corrupting the diagnostic stream (bug 77521).

Some other diagnostics that try to avoid this problem by using
a directive such as %x when the character is not printable might
use the sign-extended value of the character, printing a very
large hexadecimal value (bug 77520).

The attached patch changes the pretty printer to detect non-printable
characters in %qc and %qs directives (but not %c or %s) and print
those in hexadecimal (via "\\x%02x").


PS I used hexadecimal based on what c-format.c does but now that
I checked more carefully how %qE formats string literals I see it
uses octal.  I think hexadecimal is preferable because it avoids
ambiguity but I'm open to changing it to octal if there's a strong
preference for it.  Incidentally, %qE too suffers from bug 77520
(see below).  The patch doesn't try to fix that.

$ cat z.C && gcc z.C
constexpr int i = "ABC\x7f_\x80XYZ";
z.C:1:19: error: invalid conversion from ‘const char*’ to ‘int’
 constexpr int i = "ABC\x7f_\x80XYZ";
z.C:1:19: error: ‘(int)((const char*)"ABC\177_\37777777600XYZ")’ is not
a constant expression


PR c/77520 - wrong value for extended ASCII characters in -Wformat message
PR c/77521 - %qc format directive should quote non-printable characters

2016-09-08  Martin Sebor  <mse...@redhat.com>

        PR c/77520
        PR c/77521
        * c-format.c (argument_parser::find_format_char_info): Use %qc
        format directive unconditionally.

2016-09-08  Martin Sebor  <mse...@redhat.com>

        PR c/77520
        PR c/77521
        * pretty-print.c (pp_quoted_string): New function.
        (pp_format): Call it for %c and %s directives.

2016-09-08  Martin Sebor  <mse...@redhat.com>

        PR c/77520
        PR c/77521
        * gcc.dg/pr77520.c: New test.
        * gcc.dg/pr77521.c: New test.
I was about to ack, the realized Joseph already did and you'd already installed the change :-)


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