Subject: Re: bug#34106: 27.0.50; master build failed with MSYS2/MinGW-w64

From: Andy Moreton <[email-masked]>
Date: Wed, 16 Jan 2019 17:44:10 +0000

On Thu 17 Jan 2019, Chris Zheng wrote:

> When build master branch under MS-Windows I’m seeing this
>
>   CC       pdumper.o
> pdumper.c: In function 'dump_cold_bignum':
> pdumper.c:3447:53: error: conversion from 'size_t' {aka 'long long unsigned int'} to 'mp_size_t' {aka 'long int'} may change value [-Werror=conversion]
>        mp_limb_t limb = mpz_getlimbn (bignum->value, i);
> cc1.exe: some warnings being treated as errors
>
> Because with MSYS2/MinGW-w64 the `long' is 32-bit instead of 64-bit.
>
> A explicit cast can fix it.
>
> diff --git a/src/pdumper.c b/src/pdumper.c
> index 3787408e6d..9d5ace6c38 100644
> --- a/src/pdumper.c
> +++ b/src/pdumper.c
> @@ -3444,7 +3444,7 @@ dump_cold_bignum (struct dump_context *ctx, Lisp_Object object)
>    Fputhash (object, descriptor, ctx->bignum_data);
>    for (size_t i = 0; i < nlimbs; ++i)
>      {
> -      mp_limb_t limb = mpz_getlimbn (bignum->value, i);
> +      mp_limb_t limb = mpz_getlimbn (bignum->value, (mp_size_t) i);
>        dump_write (ctx, &limb, sizeof (limb));
>      }
>  }
>
> Thank you,
>
> Chris

The MSYS2/Mingw-w64 build also has a warning:

C:/emacs/git/emacs/master/src/emacs.c: In function 'load_pdump':
C:/emacs/git/emacs/master/src/emacs.c:752:28: warning: field precision specifier '.*' expects argument of type 'int', but argument 3 has type 'size_t' {aka 'long long unsigned int'} [-Wformat=]
     sprintf (dump_file, "%.*s%s", argv0_len - 4, argv[0], suffix);
                          ~~^~     ~~~~~~~~~~~~~

The following patch fixes the warning, and fixes the bug above without
needing a cast:

diff --git a/src/emacs.c b/src/emacs.c
index c1133f2460..834f55b6f3 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -749,7 +749,7 @@ load_pdump (int argc, char **argv)
   /* Remove the .exe extension if present.  */
   argv0_len = strlen (argv[0]);
   if (argv0_len >= 4 && c_strcasecmp (argv[0] + argv0_len - 4, ".exe") == 0)
-    sprintf (dump_file, "%.*s%s", argv0_len - 4, argv[0], suffix);
+    sprintf (dump_file, "%.*s%s", (int)(argv0_len - 4), argv[0], suffix);
   else
 #endif
   sprintf (dump_file, "%s%s", argv[0], suffix);
diff --git a/src/pdumper.c b/src/pdumper.c
index 3787408e6d..db66e1ba26 100644
--- a/src/pdumper.c
+++ b/src/pdumper.c
@@ -3442,7 +3442,7 @@ dump_cold_bignum (struct dump_context *ctx, Lisp_Object object)
     dump_off_to_lisp ((mpz_sgn (bignum->value) < 0
                        ? -nlimbs : nlimbs)));
   Fputhash (object, descriptor, ctx->bignum_data);
-  for (size_t i = 0; i < nlimbs; ++i)
+  for (mp_size_t i = 0; i < nlimbs; ++i)
     {
       mp_limb_t limb = mpz_getlimbn (bignum->value, i);
       dump_write (ctx, &limb, sizeof (limb));