eliminate protected-visibility data in libc.so with vis.h preinclude

some newer binutils versions print scary warnings about protected data
because most gcc versions fail to produce the right address
references/relocations for such data that might be subject to copy
relocations. originally vis.h explicitly assigned default visibility
to all public data symbols to avoid this issue, but commit
b8dda24fe1caa901a99580f7a52defb95aedb67c removed this treatment for
stdin/out/err to work around a gcc 3.x bug, and since they don't
actually need it (because taking their addresses is not valid C).

instead, a check for the gcc 3.x bug is added to the configure check
for vis.h preinclude support; this feature will simply be disabled
when using a buggy version of gcc.

diff --git a/configure b/configure
index de357bc2221022d135d03f9a936b5b3162ed7857..d944a47ff43dd527a3cb7ad21f50905c65fd7645 100755 (executable)
--- a/configure
+++ b/configure
@@ -476,10 +476,18 @@ if test "x$visibility" = xauto ; then
 # - the -include option
 # - the attributes/pragmas used in vis.h
 # - linking code that takes the address of protected symbols
+# - gcc 3.x bug that wrongly claims declarations mismatch
 printf "checking whether global visibility preinclude works... "
-echo 'int (*fp)(void);' > "$tmpc"
-echo 'int foo(void) { }' >> "$tmpc"
-echo 'int bar(void) { fp = foo; return foo(); }' >> "$tmpc"
+cat > "$tmpc" <<EOF
+__attribute__((__visibility__("default")))
+extern struct a *const x;
+typedef struct a b;
+extern b *const x;
+b *const x;
+int (*fp)(void);
+int foo(void) { }
+int bar(void) { fp = foo; return foo(); }
+EOF
 if $CC $CFLAGS_C99FSE $CPPFLAGS $CFLAGS \
   -DSHARED -fPIC -I./src/internal -include vis.h \
   -nostdlib -shared -Wl,-Bsymbolic-functions \

diff --git a/src/internal/vis.h b/src/internal/vis.h
index a01fda182a57329bdd75fdee9cc76167087c3910..bf7a5b206e672968c7db0931d835e53b1bff7c92 100644 (file)
--- a/src/internal/vis.h
+++ b/src/internal/vis.h
@@ -11,6 +11,9 @@
  * fail to support copy relocations for protected data, so exclude all
  * exported data symbols. */
 
+__attribute__((__visibility__("default")))
+extern struct _IO_FILE *const stdin, *const stdout, *const stderr;
+
 __attribute__((__visibility__("default")))
 extern int optind, opterr, optopt, optreset, __optreset, getdate_err, h_errno, daylight, __daylight, signgam, __signgam;