GCC_EXEC_PREFIX behavior doesn't match the manual or reason and several ways. The manual says GCC_EXEC_PREFIX is a prefix for the program name, which means 'gcc' should look for 'cc1' as GCC_EXEC_PREFIX/cc1. But Strace indicates that 'gcc' looks at GCC_EXEC_PREFIX/MACHINE/VERSION/../../../.. MACHINE/bin/MACHINE/VERSION/cc1. This is a rather strange path. The manual says gcc looks using GCC_EXEC_PREFIX first, and then the usual places. That would be normal. For me, it looks in a bunch of places unrelated to GCC_EXEC_PREFIX, then the path described above, then gives up. The "bunch of places" mentioned above starts with something that is apparently based on the path by which 'gcc' was invoked, but has too many .. in it: MY_GCC_INSTALL_DIRECTORY/lib/../../lbiexec/gcc/MACHINE/VERSION/cc1. On the other hand, if I don't set GCC_EXEC_PREFIX, it properly looks at MY_GCC_INSTALL_DIRECTORY/bin/../libexec/gcc/MACHINE/VERSION/cc1. The manual says GCC_EXEC_PREFIX is used for finding subprograms and linker files, but it is apparently also used for the specs file -- GCC_EXEC_PREFIX/MACHINE/VERSION/specs . The manual says the default for GCC_EXEC_PREFIX is PREFIX/lib/gcc . But it also says when GCC_EXEC_PREFIX is not set, gcc searches based on the pathname with which it was invoked. The latter matches what the program does for me. (For clarity, I have written the above as if gcc add a slash after GCC_EXEC_PREFIX; as documented, it doesn't). Note that in these experiments, I built gcc with PREFIX = nonexistent directory to ensure no built-in path gets used. Finally, if someone works on the manual section, I highly recommend moving the environment variable section out of the "Gcc Command Options" section. It doesn't fit there; I had a hard time finding it.
Created attachment 8157 [details] strace of failure to find cc1 In this run, PREFIX is /home/bryanh/gcc . GCC_EXEC_PREFIX is /tmp2/gcc-3.4.3/lib/gcc// . /tmp2 is a symlink to /mp/hdb2 . Gcc, in the form created by 'make install', is installed in /tmp2/gcc-3.4.3 -- i.e. 'make install' created the tree at /home/bryanh/gcc and I moved it to /tmp2/gcc-3.4.3.
I think this related to PR 14435. But reading the docs (there is a section in there which is useful to read): In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with /usr/local/lib/gcc (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with -Bfoo/, GCC will search foo/bar where it would normally search /usr/local/lib/bar. These alternate directories are searched first; the standard directories come next.
Subject: Re: GCC_EXEC_PREFIX used wrong I don't see the relevance of that paragraph to either of the problem reports, since there is no search for header files involved. I don't know anything about the Gcc bug fixing process, but I see that PR 14435 is 11 months old. Has anything been changed because of it? Will it be? If code or doc needs to be written, I'd be happy to do it, but if someone else has to figure out what GCC_EXEC_PREFIX should do, that would be premature.
I this (still) a problem today (if so, let's confirm it), otherwise let's resolve it one way or the other.
A quick check of the latest manual shows the same description, and a quick strace of GCC 6.3 shows the same behavior, so my guess is no one has touched this area.