Fix s390 -Os iconv build.

Building glibc for s390 with -Os (32-bit only, with GCC 7) fails with:

In file included from ../sysdeps/s390/multiarch/8bit-generic.c:370:0,
                 from ebcdic-at-de.c:28:
../iconv/loop.c: In function '__to_generic_vx':
../iconv/loop.c:264:22: error: 'ch' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     if (((Character) >> 7) == (0xe0000 >> 7))          \
                      ^~
In file included from ebcdic-at-de.c:28:0:
../sysdeps/s390/multiarch/8bit-generic.c:340:15: note: 'ch' was declared here
      uint32_t ch;      \
               ^
../iconv/loop.c:325:7: note: in expansion of macro 'BODY'
       BODY
       ^~~~

It's fairly easy to see, looking at the (long) expansion of the BODY
macro, that this is a false positive and the relevant variable 'ch' is
always initialized before use, in one of two possible places.  As
such, disabling the warning for -Os with the DIAG_* macros is the
natural approach to fix this build failure.  However, because of the
location at which the warning is reported, the disabling needs to go
in iconv/loop.c, around the definition of UNICODE_TAG_HANDLER (not
inside the definition), as that macro definition is where the
uninitialized use is reported, whereas the code that needs to be
reasoned about to see that the warning is a false positive is in the
definition of BODY elsewhere.

Thus, the patch adds such disabling in iconv/loop.c, with a comment
pointing to the s390-specific code and a comment in the s390-specific
code pointing to the generic file to alert people to the possible need
to update one place when changing the other.  It would be possible if
desired to use #ifdef __s390__ around the disabling, though in general
we try to avoid that sort of thing in generic files.  (Or some
extremely specialized macros for "disable -Wmaybe-uninitialized in
this particular place" could be specified, defined to 0 in a lot of
different files that include iconv/loop.c and to 1 in that particular
s390 file.)

Tested that this fixed -Os compilation for s390-linux-gnu with
build-many-glibcs.py.

	* iconv/loop.c (UNICODE_TAG_HANDLER): Disable
	-Wmaybe-uninitialized for -Os.
	* sysdeps/s390/multiarch/8bit-generic.c (BODY): Add comment about
	this disabling.

diff --git a/ChangeLog b/ChangeLog
index 42e167e18ed69803423c260121b2499c40c242e5..dc0dc43a2c0b03b51efe0d6e488bd741a3d01143 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2018-03-05  Joseph Myers  <joseph@codesourcery.com>
+
+       * iconv/loop.c (UNICODE_TAG_HANDLER): Disable
+       -Wmaybe-uninitialized for -Os.
+       * sysdeps/s390/multiarch/8bit-generic.c (BODY): Add comment about
+       this disabling.
+
 2018-03-03  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
        * bits/dirent.h (__INO_T_MATCHES_INO64_T): Define regardless whether

diff --git a/iconv/loop.c b/iconv/loop.c
index 25609f13db55f2d47a52605c1be509b4977db37c..d571b593c7b8da93095f3face61cfd7930033a32 100644 (file)
--- a/iconv/loop.c
+++ b/iconv/loop.c
@@ -254,6 +254,16 @@
   }
 
 
+/* With GCC 7 when compiling with -Os for 32-bit s390 the compiler
+   warns that the variable 'ch', in the definition of BODY in
+   sysdeps/s390/multiarch/8bit-generic.c, may be used uninitialized in
+   the call to UNICODE_TAG_HANDLER in that macro.  This variable is
+   actually always initialized before use, in the prior loop if INDEX
+   is nonzero and in the following 'if' if INDEX is zero.  That code
+   has a comment referencing this diagnostic disabling; updates in one
+   place may require updates in the other.  */
+DIAG_PUSH_NEEDS_COMMENT;
+DIAG_IGNORE_Os_NEEDS_COMMENT (7, "-Wmaybe-uninitialized");
 /* Handling of Unicode 3.1 TAG characters.  Unicode recommends
    "If language codes are not relevant to the particular processing
     operation, then they should be ignored."  This macro is usually
@@ -267,6 +277,7 @@
        continue;                                                             \
       }                                                                              \
   }
+DIAG_POP_NEEDS_COMMENT;
 
 
 /* The function returns the status, as defined in gconv.h.  */

diff --git a/sysdeps/s390/multiarch/8bit-generic.c b/sysdeps/s390/multiarch/8bit-generic.c
index 8d44cd883e36913e99a54b72ea3067dde6e10070..d608beaa62cef00f559f7327536346c63c9c5628 100644 (file)
--- a/sysdeps/s390/multiarch/8bit-generic.c
+++ b/sysdeps/s390/multiarch/8bit-generic.c
@@ -358,6 +358,10 @@
                  }                                                     \
              }                                                         \
                                                                        \
+           /* iconv/loop.c disables -Wmaybe-uninitialized for a false  \
+              positive warning in this code with -Os and has a         \
+              comment referencing this code accordingly.  Updates in   \
+              one place may require updates in the other.  */          \
            UNICODE_TAG_HANDLER (ch, 4);                                \
                                                                        \
            /* This is an illegal character.  */                        \