From: Sami Tolvanen <samitolvanen@google.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
Michal Marek <michal.lkml@markovi.net>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kbuild <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] kbuild: Merge module sections if and only if CONFIG_LTO_CLANG is enabled
Date: Tue, 23 Mar 2021 11:14:05 -0700 [thread overview]
Message-ID: <CABCJKucYHQ893LS1iCHXivPS05RMDN2BpDFou306jOEbWnt1Dg@mail.gmail.com> (raw)
In-Reply-To: <YFoZBY1SqilWAmx4@google.com>
On Tue, Mar 23, 2021 at 9:36 AM Sean Christopherson <seanjc@google.com> wrote:
>
> On Tue, Mar 23, 2021, Sami Tolvanen wrote:
> > On Mon, Mar 22, 2021 at 4:44 PM Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > Merge module sections only when using Clang LTO. With gcc-10, merging
> > > sections does not appear to update the symbol tables for the module,
> > > e.g. 'readelf -s' shows the value that a symbol would have had, if
> > > sections were not merged.
> >
> > I'm fine with limiting this to LTO only, but it would be helpful to
> > understand which sections are actually getting merged here.
>
> It doesn't appear to matter which sections get merged, the tables only show the
> correct data if there is no merging whatsoever, e.g. allowing merging for any
> one of the four types (.bss, .data, .rodata and .text) results in breakage.
> AFAICT, merging any sections causes the layout to change and throw off the
> symbol tables.
Thanks for the clarification. I can reproduce this issue with gcc +
bfd if any of the sections are merged, but gcc + lld produces valid
symbol tables.
Perhaps someone more familiar with bfd can comment on whether this is
a bug or a feature, and if there's a flag we can pass to bfd that
would fix the issue. In the meanwhile, this patch looks like a
reasonable workaround to me.
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Sami
next prev parent reply other threads:[~2021-03-23 18:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 23:44 [PATCH] kbuild: Merge module sections if and only if CONFIG_LTO_CLANG is enabled Sean Christopherson
2021-03-23 16:19 ` Sami Tolvanen
2021-03-23 16:36 ` Sean Christopherson
2021-03-23 18:14 ` Sami Tolvanen [this message]
2021-03-24 22:45 ` Sean Christopherson
2021-03-31 19:30 ` Kees Cook
2021-03-31 20:07 ` Sean Christopherson
2021-04-01 21:33 ` Kees Cook
2021-03-31 19:56 ` Kees Cook
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