On 5 September 2012 16:01, Ian Lance Taylor <iant@google.com> wrote:
>...
>
> I don't know if it's a strong reason, but the problem seems to be one
> that is characteristic of a specific invocation of a compiler, rather
> than characteristic of the compiler in general. The same compiler may
> be invoked in multiple ways. In only some of those ways is it
> appropriate to avoid canonicalizing paths.
Revised version below. Adds new gcc command line flags to override
any default set by configure. Please take another look when ready.
----------
Add flags to disable system header canonicalizations.
Libcpp may canonicalize system header paths with lrealpath() for diagnostics,
dependency output, and similar. If gcc is held in a symlink farm the
canonicalized paths may be meaningless to users, and will also conflict with
build frameworks that (for example) disallow absolute paths to header files.
This change adds -f[no-]canonical-system-headers to the gcc command line, and
a configure option --[en/dis]able-canonical-system-headers to set default
behaviour, allowing the user to select whether or not to implement r186991.
Default is enabled. See also PR c++/52974.
Tested for regressions with bootstrap builds of C and C++, both with and
without configure --disable-canonical-system-headers.
Okay for trunk?
libcpp/ChangeLog
2012年09月07日 Simon Baldwin <simonb@google.com>
 * include/cpplib.h (struct cpp_options): Add canonical_system_headers.
 * files.c (find_file_in_dir): Call maybe_shorter_path() only if
 canonical_system_headers is set.
 * init.c (cpp_create_reader): Initialize canonical_system_headers.
 * configure.ac: Add new --enable-canonical-system-headers.
 * configure: Regenerate.
 * config.in: Regenerate.
gcc/ChangeLog
2012年09月07日 Simon Baldwin <simonb@google.com>
 * doc/cppopts.texi: Document -f[no-]canonical-system-headers.
 * doc/install.texi: Document --enable-canonical-system-headers.
gcc/c-family/ChangeLog
2012年09月07日 Simon Baldwin <simonb@google.com>
 * c.opt: Add f[no-]canonical-system-headers.
 * c-opts.c (c_common_handle_option): Handle
 OPT_fcanonical_system_headers.
Index: gcc/doc/cppopts.texi
===================================================================
--- gcc/doc/cppopts.texi (revision 191054)
+++ gcc/doc/cppopts.texi (working copy)
@@ -564,6 +564,10 @@ Accept universal character names in iden
 experimental; in a future version of GCC, it will be enabled by
 default for C99 and C++.
+@item -fno-canonical-system-headers
+@opindex fno-canonical-system-headers
+When preprocessing, do not shorten system header paths with canonicalization.
+
 @item -fpreprocessed
 @opindex fpreprocessed
 Indicate to the preprocessor that the input file has already been
Index: gcc/doc/install.texi
===================================================================
--- gcc/doc/install.texi (revision 191054)
+++ gcc/doc/install.texi (working copy)
@@ -1710,6 +1710,14 @@ link time when @option{-fuse-linker-plug
 This linker should have plugin support such as gold starting with
 version 2.20 or GNU ld starting with version 2.21.
 See @option{-fuse-linker-plugin} for details.
+
+@item --enable-canonical-system-headers
+@itemx --disable-canonical-system-headers
+Enable system header path canonicalization for @file{libcpp}. This can
+produce shorter header file paths in diagnostics and dependency output
+files, but these changed header paths may conflict with some compilation
+environments. Enabled by default, and may be disabled using
+@option{--disable-canonical-system-headers}.
 @end table
 @subheading Cross-Compiler-Specific Options
Index: gcc/c-family/c.opt
===================================================================
--- gcc/c-family/c.opt (revision 191054)
+++ gcc/c-family/c.opt (working copy)
@@ -755,6 +755,10 @@ Recognize built-in functions
 fbuiltin-
 C ObjC C++ ObjC++ Joined
+fcanonical-system-headers
+C ObjC C++ ObjC++
+Where shorter, use canonicalized paths to systems headers.
+
 fcheck-new
 C++ ObjC++ Var(flag_check_new)
 Check the return value of new
Index: gcc/c-family/c-opts.c
===================================================================
--- gcc/c-family/c-opts.c (revision 191054)
+++ gcc/c-family/c-opts.c (working copy)
@@ -552,6 +552,10 @@ c_common_handle_option (size_t scode, co
 handle_OPT_d (arg);
 break;
+ case OPT_fcanonical_system_headers:
+ cpp_opts->canonical_system_headers = value;
+ break;
+
 case OPT_fcond_mismatch:
 if (!c_dialect_cxx ())
 {
Index: libcpp/configure
===================================================================
--- libcpp/configure (revision 191054)
+++ libcpp/configure (working copy)
@@ -700,6 +700,7 @@ enable_rpath
 with_libiconv_prefix
 enable_maintainer_mode
 enable_checking
+enable_canonical_system_headers
 '
 ac_precious_vars='build_alias
 host_alias
@@ -1333,6 +1334,8 @@ Optional Features:
 --disable-rpath do not hardcode runtime library paths
 --enable-maintainer-mode enable rules only needed by maintainers
 --enable-checking enable expensive run-time checks
+ --enable-canonical-system-headers
+ enable or disable system headers canonicalization
 Optional Packages:
 --with-PACKAGE[=ARG] use PACKAGE [ARG=yes]
@@ -7094,6 +7097,19 @@ $as_echo "#define ENABLE_CHECKING 1" >>c
 fi
+# Check whether --enable-canonical-system-headers was given.
+if test "${enable_canonical_system_headers+set}" = set; then :
+ enableval=$enable_canonical_system_headers;
+else
+ enable_canonical_system_headers=yes
+fi
+
+if test $enable_canonical_system_headers != no; then
+
+$as_echo "#define ENABLE_CANONICAL_SYSTEM_HEADERS 1" >>confdefs.h
+
+fi
+
 case $target in
 alpha*-*-* | \
Index: libcpp/files.c
===================================================================
--- libcpp/files.c (revision 191054)
+++ libcpp/files.c (working copy)
@@ -385,7 +385,7 @@ find_file_in_dir (cpp_reader *pfile, _cp
 void **pp;
 /* We try to canonicalize system headers. */
- if (file->dir->sysp)
+ if (CPP_OPTION (pfile, canonical_system_headers) && file->dir->sysp)
 {
 char * canonical_path = maybe_shorter_path (path);
 if (canonical_path)
Index: libcpp/include/cpplib.h
===================================================================
--- libcpp/include/cpplib.h (revision 191054)
+++ libcpp/include/cpplib.h (working copy)
@@ -489,6 +489,9 @@ struct cpp_options
 /* True disables tokenization outside of preprocessing directives. */
 bool directives_only;
+
+ /* True enables canonicalization of system header file paths. */
+ bool canonical_system_headers;
 };
 /* Callback for header lookup for HEADER, which is the name of a
Index: libcpp/init.c
===================================================================
--- libcpp/init.c (revision 191054)
+++ libcpp/init.c (working copy)
@@ -28,6 +28,10 @@ along with this program; see the file CO
 #include "localedir.h"
 #include "filenames.h"
+#ifndef ENABLE_CANONICAL_SYSTEM_HEADERS
+#define ENABLE_CANONICAL_SYSTEM_HEADERS 0
+#endif
+
 static void init_library (void);
 static void mark_named_operators (cpp_reader *, int);
 static void read_original_filename (cpp_reader *);
@@ -182,6 +186,8 @@ cpp_create_reader (enum c_lang lang, cpp
 CPP_OPTION (pfile, track_macro_expansion) = 2;
 CPP_OPTION (pfile, warn_normalize) = normalized_C;
 CPP_OPTION (pfile, warn_literal_suffix) = 1;
+ CPP_OPTION (pfile, canonical_system_headers)
+ = ENABLE_CANONICAL_SYSTEM_HEADERS;
 /* Default CPP arithmetic to something sensible for the host for the
 benefit of dumb users like fix-header. */
Index: libcpp/configure.ac
===================================================================
--- libcpp/configure.ac (revision 191054)
+++ libcpp/configure.ac (working copy)
@@ -132,6 +132,16 @@ if test $enable_checking != no ; then
 [Define if you want more run-time sanity checks.])
 fi
+AC_ARG_ENABLE(canonical-system-headers,
+[ --enable-canonical-system-headers
+ enable or disable system headers canonicalization],
+[],
+enable_canonical_system_headers=yes)
+if test $enable_canonical_system_headers != no; then
+ AC_DEFINE(ENABLE_CANONICAL_SYSTEM_HEADERS,
+ 1, [Define to enable system headers canonicalization.])
+fi
+
 m4_changequote(,)
 case $target in
 alpha*-*-* | \
Index: libcpp/config.in
===================================================================
--- libcpp/config.in (revision 191054)
+++ libcpp/config.in (working copy)
@@ -11,6 +11,9 @@
 /* Define to 1 if using `alloca.c'. */
 #undef C_ALLOCA
+/* Define to enable system headers canonicalization. */
+#undef ENABLE_CANONICAL_SYSTEM_HEADERS
+
 /* Define if you want more run-time sanity checks. */
 #undef ENABLE_CHECKING
--
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