lkml.org 
[lkml]   [2021]   [Jun]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] kallsyms: strip LTO suffixes from static functions
On Mon, Jun 28, 2021 at 10:54 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Tue, Jun 22, 2021 at 1:18 PM Fangrui Song <maskray@google.com> wrote:
> >
> > On 2021-06-22, 'Nick Desaulniers' via Clang Built Linux wrote:
> > >+/*
> > >+ * LLVM mangles static functions for full LTO so that two static functions with
> > >+ * the same identifier do not collide when all code is combined into one
> > >+ * module. The scheme used converts references to foo into
> > >+ * foo.llvm.974640843467629774, for example. This can break hooking of static
> > >+ * functions with kprobes.
> > >+ */
> >
> > The comment should say ThinLTO instead.
> >
> > The .llvm.123 suffix is for global scope promotion for local linkage
> > symbols. The scheme is ThinLTO specific. This ensures that a local
>
> Oh, boy. Indeed. I had identified the mangling coming from
> getGlobalNameForLocal(), but looking at the call chain now I see:
>
> FunctionImportGlobalProcessing::processGlobalForThinLTO()
> -> FunctionImportGlobalProcessing::getPromotedName()
> -> ModuleSummaryIndex::getGlobalNameForLocal()
>
> I'm not sure then how I figured it was specific to full LTO.
>
> Android recently switched from thin LTO to full LTO, which is what I
> assumed was the cause of the bug report. Rereading our internal bug
> report, it was tested against a prior version that did the symbol
> truncation for thinLTO. I then assumed this was full LTO specific for
> whatever reason, and modified the patch to only apply to full LTO. I
> see via the above call chain that this patch is not correct. Let me
> send my original patch as a v2. b/189560201 if you're interested.

I can even see the .llvm.<number> symbol names via `llvm-nm` on
vmlinux for thinLTO builds. No such symbols exist for full LTO.

--
Thanks,
~Nick Desaulniers

\
 
 \ /
  Last update: 2021-06-28 20:22    [W:0.109 / U:0.476 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site