make distcheck fails on Github runner ubuntu-24.04 with clang compiler

[matt335672]

xrdp version

devel

Detailed xrdp version, build options

N/A

Operating system & version

Ubuntu 24.04 LTS

Installation method

other

Which backend do you use?

N/A

What desktop environment do you use?

N/A

Environment xrdp running on

N/A

What's your client?

N/A

Area(s) with issue?

Compile error

Steps to reproduce

Edit .github/workflows/build.yml and replace ubuntu-latest with ubuntu-24.04

✔️ Expected Behavior

Runner succeeds

❌ Actual Behavior

'max features with clang' fails the distcheck phase with these compilation errors:-

CC       base64.lo
  CC       fifo.lo
  CC       file.lo
  CC       guid.lo
../../../common/base64.c:196:24: error: initializing 'char *' with an expression of type 'const char[66]' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
  196 |     static const char *b64chr =
      |                        ^
  197 |         "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  198../../../common/guid.c | : 92 : 21 :   error:  passing 'const char[69]' to parameter of type 'char *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers] 
"abcdefghijklmnopqrst   u92v | w x y z "g
_      s| p        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~r
int  f199( | d e s t ,   " % 0"20X1%20324X5%60728X9%+0/2=X"-;%
0      2| X        ~~~~~~~~~~~~~~~%
02X-%02X%02X-%02X%02X-%02X%02X%02X%02X%02X%02X",
      |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../common/os_calls.h:59:40: note: passing argument to parameter 'format' here
   59 | void g_sprintf(char *dest, const char *format, ...) \
      |                                        ^
1 error generated.
1 error generated.
make[3]: *** [Makefile:589: base64.lo] Error 1
make[3]: *** Waiting for unfinished jobs....
make[3]: *** [Makefile:589: guid.lo] Error 1
../../../common/file.c:301:61: error: passing 'const char[1]' to parameter of type 'char *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
  301 |                                     list_add_strdup(values, "");
      |                                                             ^~
../../../common/list.h:146:48: note: passing argument to parameter 'str' here
  146 | list_add_strdup(struct list *self, const char *str);
      |                                                ^
1 error generated.
make[3]: *** [Makefile:589: file.lo] Error 1
make[3]: Leaving directory '/home/runner/work/xrdp/xrdp/xrdp-0.10.80/_build/sub/common'
make[2]: *** [Makefile:511: all-recursive] Error 1
make[2]: Leaving directory '/home/runner/work/xrdp/xrdp/xrdp-0.10.80/_build/sub'
make[1]: *** [Makefile:443: all] Error 2
make[1]: Leaving directory '/home/runner/work/xrdp/xrdp/xrdp-0.10.80/_build/sub'
make: *** [Makefile:728: distcheck] Error 1
Error: Process completed with exit code 2.

Inspection shows that the 'const' qualifier is being ignored in all of these places.

Looking up the log file a little way shows this line when distcheck runs configure.

checking for an ANSI C-conforming const... no

As a result, const is redefined to be /* */!

This behaviour is caused by the m4 AC_C_CONST macro.

Running the clang make distcheck on a Ubuntu 24.04 VM shows that the test program used by the macro is failing with clang for unrelated reasons.

The test program is as follows:-

1:/* confdefs.h */
2:#define PACKAGE_NAME "xrdp"
3:#define PACKAGE_TARNAME "xrdp"
4:#define PACKAGE_VERSION "0.10.80"
5:#define PACKAGE_STRING "xrdp 0.10.80"
6:#define PACKAGE_BUGREPORT "xrdp-devel@googlegroups.com"
7:#define PACKAGE_URL ""
8:#define VERSION_YEAR 2024
9:#define PACKAGE "xrdp"
10:#define VERSION "0.10.80"
11:#define HAVE_STDIO_H 1
12:#define HAVE_STDLIB_H 1
13:#define HAVE_STRING_H 1
14:#define HAVE_INTTYPES_H 1
15:#define HAVE_STDINT_H 1
16:#define HAVE_STRINGS_H 1
17:#define HAVE_SYS_STAT_H 1
18:#define HAVE_SYS_TYPES_H 1
19:#define HAVE_UNISTD_H 1
20:#define HAVE_WCHAR_H 1
21:#define STDC_HEADERS 1
22:#define _ALL_SOURCE 1
23:#define _DARWIN_C_SOURCE 1
24:#define _GNU_SOURCE 1
25:#define _HPUX_ALT_XOPEN_SOCKET_API 1
26:#define _NETBSD_SOURCE 1
27:#define _OPENBSD_SOURCE 1
28:#define _POSIX_PTHREAD_SEMANTICS 1
29:#define __STDC_WANT_IEC_60559_ATTRIBS_EXT__ 1
30:#define __STDC_WANT_IEC_60559_BFP_EXT__ 1
31:#define __STDC_WANT_IEC_60559_DFP_EXT__ 1
32:#define __STDC_WANT_IEC_60559_FUNCS_EXT__ 1
33:#define __STDC_WANT_IEC_60559_TYPES_EXT__ 1
34:#define __STDC_WANT_LIB_EXT2__ 1
35:#define __STDC_WANT_MATH_SPEC_FUNCS__ 1
36:#define _TANDEM_SOURCE 1
37:#define __EXTENSIONS__ 1
38:/* end confdefs.h.  */
40:int
41:main (void)
42:{
44:#ifndef __cplusplus
45:  /* Ultrix mips cc rejects this sort of thing.  */
46:  typedef int charset[2];
47:  const charset cs = { 0, 0 };
48:  /* SunOS 4.1.1 cc rejects this.  */
49:  char const *const *pcpcc;
50:  char **ppc;
51:  /* NEC SVR4.0.2 mips cc rejects this.  */
52:  struct point {int x, y;};
53:  static struct point const zero = {0,0};
54:  /* IBM XL C 1.02.0.0 rejects this.
55:     It does not let you subtract one const X* pointer from another in
56:     an arm of an if-expression whose if-part is not a constant
57:     expression */
58:  const char *g = "string";
59:  pcpcc = &g + (g ? g-g : 0);
60:  /* HPUX 7.0 cc rejects these. */
61:  ++pcpcc;
62:  ppc = (char**) pcpcc;
63:  pcpcc = (char const *const *) ppc;
64:  { /* SCO 3.2v4 cc rejects this sort of thing.  */
65:    char tx;
66:    char *t = &tx;
67:    char const *s = 0 ? (char *) 0 : (char const *) 0;
69:    *t++ = 0;
70:    if (s) return 0;
71:  }
72:  { /* Someone thinks the Sun supposedly-ANSI compiler will reject this.  */
73:    int x[] = {25, 17};
74:    const int *foo = &x[0];
75:    ++foo;
76:  }
77:  { /* Sun SC1.0 ANSI compiler rejects this -- but not the above. */
78:    typedef const int *iptr;
79:    iptr p = 0;
80:    ++p;
81:  }
82:  { /* IBM XL C 1.02.0.0 rejects this sort of thing, saying
83:       "k.c", line 2.27: 1506-025 (S) Operand must be a modifiable lvalue. */
84:    struct s { int j; const int *ap[3]; } bx;
85:    struct s *b = &bx; b->j = 5;
86:  }
87:  { /* ULTRIX-32 V3.1 (Rev 9) vcc rejects this */
88:    const int foo = 10;
89:    if (!foo) return 0;
90:  }
91:  return !cs[0] && !zero.x;
92:#endif
94:  ;
95:  return 0;
96:}

And the errors generated by clang are:-

conftest.c:74:16: error: variable 'foo' set but not used [-Werror,-Wunused-but-set-variable]
   74 |     const int *foo = &x[0];
      |                ^
conftest.c:79:10: error: variable 'p' set but not used [-Werror,-Wunused-but-set-variable]
   79 |     iptr p = 0;
      |          ^
2 errors generated.

Because the test program is failing, autoconf erroneously assumes that the compiler does not support const.

Solution is to remove AC_C_CONST macro which is no longer needed.

This also needs removing from the git submodule configure.ac files.

Anything else?

This is pretty complicated which is why I've raised a separate issue to cover it.