[lto] Fix symlookup in archives vs shared

[H.J. Lu]

On Tue, Apr 8, 2025 at 12:56 PM Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
>
> On 3/31/25 9:16 AM, Michael Matz wrote:
> > when a shared library defines 'foo@@FOO' (default version),
> > a static archive defines 'foo', the shared lib comes in front
> > of the archive and under effect of --as-needed, and the requesting
> > object file uses LTO, then the link editor was wrongly including
> > the definition from the static archive.  It must use the one
> > from the shared lib, like in the non-LTO or the --no-as-needed case.
> > See the added testcase that would wrongly print "FAIL" before
> > this patch.
> >
> > The problem stems from several connected problems:
> > (1) only the decorated symbol was entered into first_hash (the hash
> >      table designed to handle definition order in the pre-LTO-plugin
> >      phase of the symbol table walks)
> > (2) in the archive symbol walk only the undecorated name would be
> >      looked up in first_hash (and hence not found due to (1))
> > (3) in the archive symbol walk first_hash would only be consulted
> >      when the linker hash table had a defined symbol.  In pre-LTO
> >      phase shared lib symbols aren't entered into the linker symbol
> >      table.
> >
> > So: add also the undecorated name into first_hash when it stems from
> > a default version and consult first_hash in the archive walker also
> > for currently undefined symbols.  If it has an entry which doesn't
> > point to the archive, then it comes from an earlier library (shared or
> > static), and so _this_ archive won't provide the definition.
> This caused a number of the embedded targets to regress in their
> testsuites, typically due to an undefined symbol such as __muldf3 that
> should have been provided by libgcc.
>
> Just picking one, ft32-elf:
>
> > Tests that now fail, but worked before (110 tests):
> >
> > ft32-sim: gcc: c-c++-common/torture/vector-compare-1.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
> > ft32-sim: gcc: c-c++-common/torture/vector-compare-1.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
> > ft32-sim: gcc: gcc.c-torture/execute/20020406-1.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
> > ft32-sim: gcc: gcc.c-torture/execute/20021120-3.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
> > ft32-sim: gcc: gcc.c-torture/execute/20070201-1.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
> > ft32-sim: gcc: gcc.c-torture/execute/20121108-1.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
> > ft32-sim: gcc: gcc.c-torture/execute/920501-8.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  (test for excess errors)
>
> [ ... ]
>
> But this was pretty pervasive across the crosses.
>

Please try this:

https://sourceware.org/pipermail/binutils/2025-April/140473.html

-- 
H.J.