Re: [PATCH 2/2] strerror_r-posix: work around cygwin 1.7.9

[Bruno Haible]

Hi Eric,

> the 'strerror' module in isolation will not replace strerror, but
> if strerror_r is in use for any other reason, then the two use
> separate buffers.

Very nice. Good improvement.

I'm applying a couple of follow-up tweaks:
  - In gl_FUNC_STRERROR, we don't need to emit code in configure that tests
    the value of gl_cv_func_strerror_r_works if that variable cannot have
    been set.
  - gl_FUNC_STRERROR_R_WORKS does not need to require 
gl_HEADER_STRING_H_DEFAULTS,
    since it doesn't set HAVE_* or REPLACE_* variables. It's gl_FUNC_STRERROR_R
    which needs to require it.
  - gl_PREREQ_STRERROR_R needs to test whether __xpg_strerror_r exists, since
    lib/strerror_r.c tests HAVE___XPG_STRERROR_R. Until two weeks ago, there
    was the assumption that it had already been tested by gl_FUNC_STRERROR_R,
    but that's not the case any more since we have added the 'test -z 
"$ERRNO_H"'
    and since the list of platforms that have __xpg_strerror_r now includes
    Cygwin (for which "$ERRNO_H" ends up non-empty).
  - Fix a couple of unclear comments.


2011-06-08  Bruno Haible  <address@hidden>

        strerror_r-posix: Tweaks.
        * m4/strerror.m4 (gl_FUNC_STRERROR): Omit the code that tests
        gl_cv_func_strerror_r_works if gl_FUNC_STRERROR_R_WORKS is not present.
        * m4/strerror_r.m4 (gl_FUNC_STRERROR_R_WORKS): Fix AC_CACHE_CHECK
        message. Move gl_HEADER_STRING_H_DEFAULTS invocation from here...
        (gl_FUNC_STRERROR_R): ... to here.
        (gl_PREREQ_STRERROR_R): Test for __xpg_strerror_r.

--- m4/strerror.m4.orig Wed Jun  8 12:21:39 2011
+++ m4/strerror.m4      Wed Jun  8 11:52:01 2011
@@ -35,10 +35,13 @@
       dnl integers. Replace it.
       REPLACE_STRERROR=1
     fi
-    dnl If the system's strerror_r clobbers strerror, we must replace strerror.
-    case $gl_cv_func_strerror_r_works in
-      *no) REPLACE_STRERROR=1 ;;
-    esac
+    m4_ifdef([gl_FUNC_STRERROR_R_WORKS], [
+      dnl If the system's strerror_r or __xpg_strerror_r clobbers strerror's
+      dnl buffer, we must replace strerror.
+      case "$gl_cv_func_strerror_r_works" in
+        *no) REPLACE_STRERROR=1 ;;
+      esac
+    ])
   else
     dnl The system's strerror() cannot know about the new errno values we add
     dnl to <errno.h>. Replace it.
--- m4/strerror_r.m4.orig       Wed Jun  8 12:21:39 2011
+++ m4/strerror_r.m4    Wed Jun  8 12:00:47 2011
@@ -6,6 +6,7 @@
 
 AC_DEFUN([gl_FUNC_STRERROR_R],
 [
+  AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
   AC_REQUIRE([gl_FUNC_STRERROR_R_WORKS])
 
   dnl Persuade Solaris <string.h> to declare strerror_r().
@@ -26,7 +27,7 @@
           *no) REPLACE_STRERROR_R=1 ;;
         esac
       else
-        dnl The system's strerror() has a wrong signature. Replace it.
+        dnl The system's strerror_r() has a wrong signature. Replace it.
         REPLACE_STRERROR_R=1
       fi
     else
@@ -39,15 +40,15 @@
 
 # Prerequisites of lib/strerror_r.c.
 AC_DEFUN([gl_PREREQ_STRERROR_R], [
+  dnl glibc >= 2.3.4 and cygwin 1.7.9 have a function __xpg_strerror_r.
+  AC_CHECK_FUNCS([__xpg_strerror_r])
   AC_CHECK_FUNCS_ONCE([catgets])
-  :
 ])
 
 # Detect if strerror_r works, but without affecting whether a replacement
 # strerror_r will be used.
 AC_DEFUN([gl_FUNC_STRERROR_R_WORKS],
 [
-  AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
   AC_REQUIRE([gl_HEADER_ERRNO_H])
   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
 
@@ -120,10 +121,10 @@
         dnl The system's strerror() has a wrong signature.
         dnl glibc >= 2.3.4 and cygwin 1.7.9 have a function __xpg_strerror_r.
         AC_CHECK_FUNCS([__xpg_strerror_r])
-        dnl glibc < 2.14 does not populate buf on failure
-        dnl cygwin < 1.7.10 clobbers strerror
+        dnl In glibc < 2.14, __xpg_strerror_r does not populate buf on failure.
+        dnl In cygwin < 1.7.10, __xpg_strerror_r clobbers strerror's buffer.
         if test $ac_cv_func___xpg_strerror_r = yes; then
-          AC_CACHE_CHECK([whether strerror_r works],
+          AC_CACHE_CHECK([whether __xpg_strerror_r works],
             [gl_cv_func_strerror_r_works],
             [AC_RUN_IFELSE(
                [AC_LANG_PROGRAM(
@@ -147,8 +148,8 @@
                   ]])],
                [gl_cv_func_strerror_r_works=yes],
                [gl_cv_func_strerror_r_works=no],
-               [dnl guess no on all platforms that have __xpg_strerror_r,
-                dnl at least until fixed glibc and cygwin are more common
+               [dnl Guess no on all platforms that have __xpg_strerror_r,
+                dnl at least until fixed glibc and cygwin are more common.
                 gl_cv_func_strerror_r_works="guessing no"
                ])
             ])

-- 
In memoriam Larisa Yudina <http://en.wikipedia.org/wiki/Larisa_Yudina>