Re: Bug in gcc.c for_each_path() (leads to invalid crt0.o selection)?

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

Hallo Joseph,

On 05/12/16 23:02, Joseph Myers wrote:
> On Mon, 5 Dec 2016, Sebastian Huber wrote:
>
> > If we assume that the command line order determines the search order, then its
> > not clear why for_each_path() first iterates for all paths with the multilib
> > postfix and then without. Shouldn't it iterate over all paths and check
> > with/without multilib postfix in each step?
> No.  The directory without the multilib postfix is generally the directory
> for another multilib, i.e. always wrong to search, and in case the library
> appears earlier in the non-multilib directories than the multilib ones,
> mixing the search paths (and there may already be some unwanted mixing
> when sysroots are involved) would result in the wrong library being
> chosen.
>
> Unfortunately, getting rid of the search of non-multilib directories
> completely is hard.  It was removed in r96915
> <https://gcc.gnu.org/ml/gcc-patches/2004-11/msg01895.html>.  Then this was
> reverted in <https://gcc.gnu.org/ml/gcc-patches/2005-12/msg00818.html>.
> Furthermore, it turns out there is a case where the existing multilib
> configuration machinery cannot express things correctly without searching
> non-multilib directories.  Specifically, consider the combination of
> MULTILIB_OSDIRNAMES with sysroot suffixes.  This is used by
> config/mips/{t-mti-linux,mti-linux.h}, for example.
>
> MULTILIB_OSDIRNAMES provides directory names used in two ways: relative to
> $target/lib/ in the GCC installation, and relative to lib/ and usr/lib/ in
> a sysroot.  For the latter, we want names such as plain ../lib64, but
> these cannot be used outside the sysroot because different multilibs would
> be mapped to the same directory.  The solution to this issue relies on
> searches without multilib suffixes: you define STARTFILE_PREFIX_SPEC
> (which used to be used more widely before MULTILIB_OSDIRNAMES was added in
> the first place) so sysroot libraries can be found by the combination of
> (sysroot, sysroot suffix, startfile prefix, *no* multilib suffix).
>
> So while this case of MULTILIB_OSDIRNAMES with multiple sysroots makes it
> hard to eliminate the search of non-multilib directories, they should be
> searched as late as possible to reduce the risk of problems from the wrong
> libraries being found.

thanks for the detailed explanation. I guess, then the root cause for my 
problem is that the Newlib provided crt0.o files in the build tree are 
not in the same relative location of the installation tree. In the build 
tree, they reside in a "newlib" subdirectory. I changed the Newlib build 
flags set by GCC to use -L instead of -B and this seems to work (comment 
is wrong now). Does it make sense to submit such a patch or has it maybe 
some nasty side-effects?

diff --git a/configure b/configure
index b6389e4..3c84acb 100755
--- a/configure
+++ b/configure
@@ -7497,7 +7497,7 @@ case " $target_configdirs " in
       # If we're building newlib, use its generic headers last, but search
       # for any libc-related directories first (so make it the last -B
       # switch).
-      FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' 
-B$$r/$(TARGET_SUBDIR)/newlib/ -isystem 
$$r/$(TARGET_SUBDIR)/newlib/targ-include -isystem $$s/newlib/libc/include'
+      FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' 
-L$$r/$(TARGET_SUBDIR)/newlib/ -isystem 
$$r/$(TARGET_SUBDIR)/newlib/targ-include -isystem $$s/newlib/libc/include'

       # If we're building libgloss, find the startup file, simulator 
library
       # and linker script.
diff --git a/configure.ac b/configure.ac
index 51ee705..ca6fb88 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3086,7 +3086,7 @@ case " $target_configdirs " in
       # If we're building newlib, use its generic headers last, but search
       # for any libc-related directories first (so make it the last -B
       # switch).
-      FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' 
-B$$r/$(TARGET_SUBDIR)/newlib/ -isystem 
$$r/$(TARGET_SUBDIR)/newlib/targ-include -isystem $$s/newlib/libc/include'
+      FLAGS_FOR_TARGET=$FLAGS_FOR_TARGET' 
-L$$r/$(TARGET_SUBDIR)/newlib/ -isystem 
$$r/$(TARGET_SUBDIR)/newlib/targ-include -isystem $$s/newlib/libc/include'

       # If we're building libgloss, find the startup file, simulator 
library
       # and linker script.
diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index c7b1eaf..9e8dea1 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -3809,7 +3809,7 @@ site.exp: ./config.status Makefile
        @if [ -d $(objdir)/../$(target_subdir)/newlib ] \
            && [ "${host}" != "${target}" ]; then \
          echo "set newlib_cflags 
\"-I$(objdir)/../$(target_subdir)/newlib/targ-include 
-I\$$srcdir/../newlib/libc/include\"" >> ./site.tmp; \
-         echo "set newlib_ldflags 
\"-B$(objdir)/../$(target_subdir)/newlib/\"" >> ./site.tmp; \
+         echo "set newlib_ldflags 
\"-L$(objdir)/../$(target_subdir)/newlib/\"" >> ./site.tmp; \
          echo "append CFLAGS \" \$$newlib_cflags\"" >> ./site.tmp; \
          echo "append CXXFLAGS \" \$$newlib_cflags\"" >> ./site.tmp; \
          echo "append LDFLAGS \" \$$newlib_ldflags\"" >> ./site.tmp; \

--
Sebastian Huber, embedded brains GmbH

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