coredump: Document coredump code exclusively used by cell spufs

Oleg Nesterov recently asked[1] why is there an unshare_files in
do_coredump.  After digging through all of the callers of lookup_fd it
turns out that it is
arch/powerpc/platforms/cell/spufs/coredump.c:coredump_next_context
that needs the unshare_files in do_coredump.

Looking at the history[2] this code was also the only piece of coredump code
that required the unshare_files when the unshare_files was added.

Looking at that code it turns out that cell is also the only
architecture that implements elf_coredump_extra_notes_size and
elf_coredump_extra_notes_write.

I looked at the gdb repo[3] support for cell has been removed[4] in binutils
2.34.  Geoff Levand reports he is still getting questions on how to
run modern kernels on the PS3, from people using 3rd party firmware so
this code is not dead.  According to Wikipedia the last PS3 shipped in
Japan sometime in 2017.  So it will probably be a little while before
everyone's hardware dies.

Add some comments briefly documenting the coredump code that exists
only to support cell spufs to make it easier to understand the
coredump code.  Eventually the hardware will be dead, or their won't
be userspace tools, or the coredump code will be refactored and it
will be too difficult to update a dead architecture and these comments
make it easy to tell where to pull to remove cell spufs support.

[1] https://lkml.kernel.org/r/20201123175052.GA20279@redhat.com
[2] 179e037fc137 ("do_coredump(): make sure that descriptor table isn't shared")
[3] git://sourceware.org/git/binutils-gdb.git
[4] abf516c6931a ("Remove Cell Broadband Engine debugging support").
Link: https://lkml.kernel.org/r/87h7pdnlzv.fsf_-_@x220.int.ebiederm.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index b6b3d052ca86dee2084da5d806d7848e80cac1c1..c1996f0aeaede6e86e9eaf091d9617dd346685da 100644 (file)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -2198,6 +2198,7 @@ static int elf_core_dump(struct coredump_params *cprm)
        {
                size_t sz = get_note_info_size(&info);
 
+               /* For cell spufs */
                sz += elf_coredump_extra_notes_size();
 
                phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL);
@@ -2261,6 +2262,7 @@ static int elf_core_dump(struct coredump_params *cprm)
        if (!write_note_info(&info, cprm))
                goto end_coredump;
 
+       /* For cell spufs */
        if (elf_coredump_extra_notes_write(cprm))
                goto end_coredump;
 

diff --git a/fs/coredump.c b/fs/coredump.c
index abf8072352620a4f4bb8c2563cdd9d6fbede7eee..3ff17eea812e27c9673c1a93411d20cf4433776b 100644 (file)
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -790,6 +790,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
        }
 
        /* get us an unshared descriptor table; almost always a no-op */
+       /* The cell spufs coredump code reads the file descriptor tables */
        retval = unshare_files();
        if (retval)
                goto close_fail;