linux-kernel - Re: [PATCH] serial: icom: Fix namespace collision and startup() section placement with -ffunction-sections

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Message-ID: <20251119084435.GJ4068168@noisy.programming.kicks-ass.net>
Date: Wed, 19 Nov 2025 09:44:35 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] serial: icom: Fix namespace collision and startup()
 section placement with -ffunction-sections

On Wed, Nov 19, 2025 at 09:43:15AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 19, 2025 at 07:58:05AM +0100, Jiri Slaby wrote:
> > On 19. 11. 25, 7:27, Josh Poimboeuf wrote:
> > > When compiling the kernel with -ffunction-sections (e.g., for LTO,
> > > livepatch, dead code elimination, AutoFDO, or Propeller), the startup()
> > > function gets compiled into the .text.startup section.  In some cases it
> > > can even be cloned into .text.startup.constprop.0 or
> > > .text.startup.isra.0.
> > > 
> > > However, the .text.startup and .text.startup.* section names are already
> > > reserved for use by the compiler for __attribute__((constructor)) code.
> > > 
> > > This naming conflict causes the vmlinux linker script to wrongly place
> > > startup() function code in .init.text, which gets freed during boot.
> > 
> > This sounds rather error-prone. What are the patterns supposed to match
> > actually? Can't *those* real victims™ be renamed to something less common
> > instead?
> 
> Yeah, this is a terrible mess. The problem is that when linking objects
> build with and without -ffunction-sections you can no longer uniquely
> identify what's what :-(
> 
> As long as its consistently one or the other it works, but if you mix
> them constructors and normal function like this get mixed up.
> 
> In another thread I've suggested this might be a toolchain bug, but even
> if they agree and fix it, we still stuck with the old compilers. And I'm
> not sure the toolchain people are agreeing there's anything wrong here
> -- the argument is that you shouldn't be mixing this or somesuch.
> 
> Anyway, objtool has a warning for this, so new occurrences should be
> flagged before they get introduced. But yes, we need to make the tree
> clean first.

Also, that objtool warning only really works architectures that have
objtool on, other archs can indeed silently create fail :-(