linux-kernel - Re: [PATCH v3 17/64] objtool: Fix weak symbol detection

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Message-ID: <5x6xrmb6srf6arbx354jegakel2pe6b3eh3xokemjeuagbm7s6@ywwoh4gbyhyu>
Date: Fri, 27 Jun 2025 08:42:11 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>, 
	Joe Lawrence <joe.lawrence@...hat.com>, live-patching@...r.kernel.org, Song Liu <song@...nel.org>, 
	laokz <laokz@...mail.com>, Jiri Kosina <jikos@...nel.org>, 
	Marcos Paulo de Souza <mpdesouza@...e.com>, Weinan Liu <wnliu@...gle.com>, 
	Fazla Mehrab <a.mehrab@...edance.com>, Chen Zhongjin <chenzhongjin@...wei.com>, 
	Puranjay Mohan <puranjay@...nel.org>, Dylan Hatch <dylanbhatch@...gle.com>
Subject: Re: [PATCH v3 17/64] objtool: Fix weak symbol detection

On Fri, Jun 27, 2025 at 11:13:10AM +0200, Peter Zijlstra wrote:
> On Thu, Jun 26, 2025 at 04:55:04PM -0700, Josh Poimboeuf wrote:
> > find_symbol_hole_containing() fails to find a symbol hole (aka stripped
> > weak symbol) if its section has no symbols before the hole.  This breaks
> > weak symbol detection if -ffunction-sections is enabled.
> > 
> > Fix that by allowing the interval tree to contain section symbols, which
> > are always at offset zero for a given section.
> > 
> > Fixes a bunch of (-ffunction-sections) warnings like:
> > 
> >   vmlinux.o: warning: objtool: .text.__x64_sys_io_setup+0x10: unreachable instruction
> > 
> > Fixes: 4adb23686795 ("objtool: Ignore extra-symbol code")
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> > ---
> >  tools/include/linux/interval_tree_generic.h | 2 +-
> >  tools/objtool/elf.c                         | 8 ++++----
> >  2 files changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/tools/include/linux/interval_tree_generic.h b/tools/include/linux/interval_tree_generic.h
> > index aaa8a0767aa3..c0ec9dbdfbaf 100644
> > --- a/tools/include/linux/interval_tree_generic.h
> > +++ b/tools/include/linux/interval_tree_generic.h
> > @@ -77,7 +77,7 @@ ITSTATIC void ITPREFIX ## _remove(ITSTRUCT *node,			      \
> >   *   Cond2: start <= ITLAST(node)					      \
> >   */									      \
> >  									      \
> > -static ITSTRUCT *							      \
> > +ITSTATIC ITSTRUCT *							      \
> >  ITPREFIX ## _subtree_search(ITSTRUCT *node, ITTYPE start, ITTYPE last)	      \
> >  {									      \
> >  	while (true) {							      \
> 
> IIRC this file is a direct copy from the kernel; this should probably be
> changed in both?

Ok.  We should probably enforce that with the sync-check script.

-- 
Josh