Re: GCC 6 symbol poisoning and c++ header usage is fragile

[Richard Biener <richard dot guenther at gmail dot com>]

On Thu, Apr 21, 2016 at 1:11 PM, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> building gcc6 using musl based gcc6 fails with symbol poisoning error
> (details at the end of the mail).
>
> the root cause is c++: c++ headers include random libc headers with
> _GNU_SOURCE ftm so all sorts of unexpected symbols are defined/declared.
>
> since it's unlikely the c++ standard gets fixed (to properly specify
> the namespace rules) it is not acceptable to include std headers after
> system.h, where the poisoning happens, because trivial libc header
> change will break the build.
>
> c++ header use in gcc seems inconsistent, e.g. there are cases where
> - <string> is included before system.h (go-system.h)
> - <string> is included after system.h (indirectly through <map>)
> - <string> is included in system.h because INCLUDE_STRING is defined.
> - <new> is included in system.h and in source files using it.. sometimes
>
> i think it should be consistently before system.h (i'm not sure what's
> going on with the INCLUDE_STRING macro), fortunately not many files are
> affected in gcc/:

system headers should be included from _within_ system.h.  To avoid including
them everywhere we use sth like

/* Include <string> before "safe-ctype.h" to avoid GCC poisoning
   the ctype macros through safe-ctype.h */

#ifdef __cplusplus
#ifdef INCLUDE_STRING
# include <string>
#endif
#endif

so sources do

#define INCLUDE_STRING
#include "config.h"
#include "system.h"

So the <string> cases can be simplified with INCLUDE_STRING and the
<new> case should be added similarly (unless we decide <new> is cheap
enough to be always included).

Richard.

> auto-profile.c
> diagnostic.c
> graphite-isl-ast-to-gimple.c
> ipa-icf.c
> ipa-icf-gimple.c
> pretty-print.c
> toplev.c
>
> i can prepare a patch moving the c++ includes up and i'm open to
> other suggestions. (including libc headers is also problematic because
> of _GNU_SOURCE, but still safer than what is happening in c++ land
> where #include <map> makes all locale.h, pthread.h, time.h, sched.h,
> etc symbols visible).
>
>
> x86_64-linux-musl-g++ -fno-PIE -c   -g -O2 -DIN_GCC     -fno-exceptions -fno-rtti -fasynchronous-unwind-tables
> -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribute -Woverloaded-virtual -pedantic
> -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings   -DHAVE_CONFIG_H -I. -I. -I/src/gcc/gcc
> -I/src/gcc/gcc/. -I/src/gcc/gcc/../include -I/src/gcc/gcc/../libcpp/include -I/build/host-tools/include
> -I/build/host-tools/include -I/build/host-tools/include  -I/src/gcc/gcc/../libdecnumber
> -I/src/gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I/src/gcc/gcc/../libbacktrace   -o auto-profile.o -MT
> auto-profile.o -MMD -MP -MF ./.deps/auto-profile.TPo /src/gcc/gcc/auto-profile.c
> In file included from /tool/x86_64-linux-musl/include/pthread.h:30:0,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/x86_64-linux-musl/bits/gthr-default.h:35,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/x86_64-linux-musl/bits/gthr.h:148,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/ext/atomicity.h:35,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/bits/basic_string.h:39,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/string:52,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/stdexcept:39,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/array:39,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/tuple:39,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/bits/stl_map.h:63,
>                  from /tool/x86_64-linux-musl/include/c++/6.0.1/map:61,
>                  from /src/gcc/gcc/auto-profile.c:36:
> /tool/x86_64-linux-musl/include/sched.h:74:7: error: attempt to use poisoned "calloc"
>  void *calloc(size_t, size_t);
>        ^
> /tool/x86_64-linux-musl/include/sched.h:114:36: error: attempt to use poisoned "calloc"
>  #define CPU_ALLOC(n) ((cpu_set_t *)calloc(1,CPU_ALLOC_SIZE(n)))
>                                     ^
>