Message-ID: <20251112132557.6928f799@pumpkin>
Date: Wed, 12 Nov 2025 13:25:57 +0000
From: David Laight <david.laight.linux@...il.com>
To: Michael Kelley <mhklinux@...look.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
 "linux-kernel@...r.kernel.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"
 <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>, Peter
 Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4 49/63] objtool/klp: Add --checksum option to generate
 per-function checksums

On Wed, 12 Nov 2025 04:32:02 +0000
Michael Kelley <mhklinux@...look.com> wrote:

> From: Josh Poimboeuf <jpoimboe@...nel.org> Sent: Tuesday, November 11, 2025 8:04 PM
> > 
> > On Wed, Nov 12, 2025 at 02:26:18AM +0000, Michael Kelley wrote:  
> > > > I've been able to debug this.  Two problems:
> > > >
> > > > 1) On Ubuntu (both 20.04 and 24.04), /bin/sh and /usr/bin/sh are symlinks
> > > > to "dash" (not "bash"). So the "shell" command in "make" invokes dash. The
> > > > man page for dash shows that the built-in echo command accepts only -n as
> > > > an option. The -e behavior of processing "\n" and similar sequences is always
> > > > enabled. So on my Ubuntu systems, the "-e" is ignored by echo and becomes
> > > > part of the C source code sent to gcc, and of course it barfs. Dropping the -e
> > > > makes it work for me (and the \n is handled correctly), but that might not work
> > > > with other shells. Using "/bin/echo" with the -e solves the problem in a more
> > > > compatible way across different shells.  
> > 
> > Ah.  I think we can use "printf" here.

Much better than echo - and a bultin on most shells.

> >   
> > > > 2) With make v4.2.1 on my Ubuntu 20.04 system, the "#" character in the
> > > > "#include" added to the echo command is problematic. "make" seems to be
> > > > treating it as a comment character, though I'm not 100% sure of that
> > > > interpretation. Regardless, the "#" causes a syntax error in the "make" shell
> > > > command. Adding a backslash before the "#" solves that problem. On an Ubuntu
> > > > 24.04 system with make v4.3, the "#" does not cause any problems. (I tried to put
> > > > make 4.3 on my Ubuntu 20.04 system, but ran into library compatibility problems
> > > > so I wasn’t able to definitively confirm that it is the make version that changes the
> > > > handling of the "#"). Unfortunately, adding the backslash before the # does *not*
> > > > work with make v4.3. The backslash becomes part of the C source code sent to
> > > > gcc, which barfs. I don't immediately have a suggestion on how to resolve this
> > > > in a way that is compatible across make versions.  
> > >
> > > Using "\043" instead of the "#" is a compatible solution that works in make
> > > v4.2.1 and v4.3 and presumably all other versions as well.  
> > 
> > Hm... I've seen similar portability issues with "," for which we had to
> > change it to "$(comma)" which magically worked for some reason that I am
> > forgetting.
> > 
> > Does "$(pound)" work?  This seems to work here:

Please not 'pound' - that is the uk currency symbol (not what US greengrocers
scrawl for lb).

	David

> > 
> >         HAVE_XXHASH = $(shell printf "$(pound)include <xxhash.h>\nXXH3_state_t *state;int main() {}" | \
> >   
> 
> Yes, the above line works in my Ubuntu 20.04 and 24.04 environments.
> It properly detects the presence and absence of xxhash 0.8. Seems like a
> good solution to me.
> 
> Michael

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