[Bug bootstrap/100431] New: Fixes to enable compiling with -Werror=format-security

[Bug bootstrap/100431] New: Fixes to enable compiling with -Werror=format-security

[joey.dumont at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100431

            Bug ID: 100431
           Summary: Fixes to enable compiling with -Werror=format-security
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: joey.dumont at gmail dot com
  Target Milestone: ---

Created attachment 50757
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50757&action=edit
Patch to fix -Werror=format-security errors

As mentioned in bug 100207, Arch Linux recently starting compiling its packages
with the -Werror=format-security option. In this bug report, I attach two
patches that enable compiling gcc with that flag. 

The first patch expliclity adds "%s" format strings to functions that pass its
arguments to printf. 

However, during my testing, I found that libgcc uses -Wno-format in its CFLAGS,
making the flags inconsistent. It seemed that adding the
--enable-build-format-warnings should remove the -Wno-format option from the
compile flags, but it didn't seem to work as expected, leading to errors like
this: 

/build/gcc/src/gcc-build/./gcc/xgcc -B/build/gcc/src/gcc-build/./gcc/
-B/usr/x86_64-pc-linux-gnu/bin/ -B/usr/x86_64-pc-linux-gnu/lib/ -isystem
/usr/x86_64-pc-linux-gnu/include -isystem /usr/x86_64-pc-linux-gnu/sys-include 
 -fno-checking -g -march=x86-64 -mtune=generic -O2 -fno-plt -fexceptions
-Wp,-D_FORTIFY_SOURCE=2,-D_GLIBCXX_ASSERTIONS -Wformat -Werror=format-security
-fstack-clash-protection -fcf-protection -m32 -O2  -g -march=x86-64
-mtune=generic -O2  -fno-plt -fexceptions        
-Wp,-D_FORTIFY_SOURCE=2,-D_GLIBCXX_ASSERTIONS         -Wformat
-Werror=format-security         -fstack-clash-protection -fcf-protection
-DIN_GCC    -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual
-Wno-error=format-diag -Wno-format -Wstrict-prototypes -Wmissing-prototypes
-Wno-error=format-diag -Wold-style-definition  -isystem ./include  -fpic
-mlong-double-80 -DUSE_ELF_SYMVER -fcf-protection -mshstk -g -DIN_LIBGCC2
-fbuilding-libgcc -fno-stack-protector  -fpic -mlong-double-80 -DUSE_ELF_SYMVER
-fcf-protection -mshstk -I. -I. -I../../.././gcc -I/build/gcc/src/gcc/libgcc
-I/build/gcc/src/gcc/libgcc/. -I/build/gcc/src/gcc/libgcc/../gcc
-I/build/gcc/src/gcc/libgcc/../include
-I/build/gcc/src/gcc/libgcc/config/libbid -DENABLE_DECIMAL_BID_FORMAT
-DHAVE_CC_TLS  -DUSE_TLS -o _muldi3.o -MT _muldi3.o -MD -MP -MF _muldi3.dep
-DL_muldi3 -c /build/gcc/src/gcc/libgcc/libgcc2.c -fvisibility=hidden
-DHIDE_EXPORTS
cc1: error: ‘-Wformat-security’ ignored without ‘-Wformat’
[-Werror=format-security]

I am not sure how these flags are set. In any case, the second patch works
around the issue by changing the --enable-build-format-warnings to add
-Wno-format-security to the flags, making the flags consistent again.

I think the first patch is a genuine fix, but I'm not sure about the second. I
would have expected --enable-build-format-warnings to entirely remove the
-Wno-format option, but it seems to stick somewhere in the build process, and I
can't see where.

[Bug bootstrap/100431] Fixes to enable compiling with -Werror=format-security

[joey.dumont at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100431

--- Comment #1 from Joey Dumont <joey.dumont at gmail dot com> ---
Created attachment 50758
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50758&action=edit
Workaround for -Wno-format flag injected during build process.

[Bug bootstrap/100431] Fixes to enable compiling with -Werror=format-security

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100431

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Comment on attachment 50757
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50757
Patch to fix -Werror=format-security errors

I doubt you have properly tested it, because it is clearly buggy.

          const char *message = (result & CPP_N_UNSIGNED) == CPP_N_UNSIGNED
                                ? N_("use of C++23 %<size_t%> integer
constant")
                                : N_("use of C++23 %<make_signed_t<size_t>%>
integer constant");
          cpp_warning_with_line (pfile, CPP_W_SIZE_T_LITERALS,
                                 virtual_location, 0, message);
Changing this to "%s", message obviously breaks it, it will not print
use of C++23 'size_t' integer constant (or with UTF-8 quotes etc. and with
colors etc.), but
use of C++23 %<size_t%> integer constant

[Bug bootstrap/100431] Fixes to enable compiling with -Werror=format-security

[joey.dumont at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100431

--- Comment #3 from Joey Dumont <joey.dumont at gmail dot com> ---
I had tested with a simple printf: 

#include <stdio.h>

#ifndef N_
# define N_(msgid) msgid
#endif

int
main(int argc, char* argv[]) {
  printf(N_("use of C++23 %<size_t%> integer constant"));
  printf(N_("use of C++23 %<make_signed_t<size_t>%> integer constant"));

  return 0;
}

which prints the same thing with or without the "%s" format string. 

I've been trying to trace where pfile->cb.diagnostic is set to see how the
output is actually processed, but I haven't found it yet. 

Thanks for the feedback!

[Bug bootstrap/100431] Fixes to enable compiling with -Werror=format-security

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100431

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
%< and %> are GCC diagnostics format specifiers, not printf.
They are more similar to e.g. GNU printf %m , something that doesn't take any
va_arg, but is interpreted.
Try
printf ("%m\n");
vs.
printf ("%s", "%m\n");
to see the difference.
Anyway, for this case either using the conditional directly in the
cpp_warning_with_line argument instead of in initializer of a temporary, or two
cpp_warning_with_line calls each with a separate string would do.
Anyway, I strongly doubt your patch covers everything, I can see e.g.
gcc/c/c-convert.c:81:31: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/c/c-typeck.c:3681:28: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/c/c-typeck.c:4433:42: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/c/c-typeck.c:6587:43: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/c/c-typeck.c:11679:42: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/c-family/c-common.c:6358:30: warning: format not a string literal and no
format arguments [-Wformat-security]
gcc/c-family/c-common.c:6362:33: warning: format not a string literal and no
format arguments [-Wformat-security]
gcc/fold-const.c:303:42: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/ipa-devirt.c:951:47: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/analyzer/program-state.cc:1153:20: warning: format not a string literal and
no format arguments [-Wformat-security]
gcc/diagnostic.c:1887:52: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/cp/cvt.c:725:26: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/cp/error.c:799:20: warning: spurious leading punctuation sequence ‘<’ in
format [-Wformat-diag]
gcc/cp/error.c:799:20: warning: spurious trailing punctuation sequence ‘>’ in
format [-Wformat-diag]
gcc/cp/error.c:799:20: warning: spurious leading punctuation sequence ‘<’ in
format [-Wformat-diag]
gcc/cp/error.c:799:20: warning: spurious trailing punctuation sequence ‘>’ in
format [-Wformat-diag]
gcc/cp/decl.c:3485:22: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/cp/typeck.c:4721:24: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/cp/typeck.c:6630:24: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/cp/pt.c:19640:20: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/collect2.c:2422:37: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/collect-utils.c:200:37: warning: format not a string literal and no format
arguments [-Wformat-security]
gcc/lto-wrapper.c:1606:31: warning: format not a string literal and no format
arguments [-Wformat-security]
and you've only touched the gcc/diagnostic.c case from that.

[Bug bootstrap/100431] Fixes to enable compiling with -Werror=format-security

[joey.dumont at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100431

--- Comment #5 from Joey Dumont <joey.dumont at gmail dot com> ---
I just started looking at these other cases (for some reason I didn't see them
in my initial compilation), but I am not sure what format specifiers should be
used. Are the format specifiers used by __gcc_tdiag__ documented somewhere? I
tried grepping through the source, but couldn't find anything.