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Date:   Tue, 04 Oct 2022 10:30:18 -0700
From:   "Andy Lutomirski" <luto@kernel.org>
To:     "Ali Raza" <aliraza@bu.edu>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Cc:     "Jonathan Corbet" <corbet@lwn.net>, masahiroy@kernel.org,
        michal.lkml@markovi.net,
        "Nick Desaulniers" <ndesaulniers@google.com>,
        "Thomas Gleixner" <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, "Borislav Petkov" <bp@alien8.de>,
        "Dave Hansen" <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Kees Cook" <keescook@chromium.org>,
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        "Al Viro" <viro@zeniv.linux.org.uk>,
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        linux-arch@vger.kernel.org,
        "the arch/x86 maintainers" <x86@kernel.org>, rjones@redhat.com,
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        lwoodman@redhat.com, mboydmcse@gmail.com, okrieg@bu.edu,
        rmancuso@bu.edu
Subject: Re: [RFC UKL 02/10] x86/boot: Load the PT_TLS segment for Unikernel configs
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Precedence: bulk

On Mon, Oct 3, 2022, at 3:21 PM, Ali Raza wrote:
> The kernel normally skips loading this segment as it is not inlcuded in
> standard builds. However, when linked with an application in the Unikernel
> configuration the segment will be present. Load PT_TLS when configured as a
> unikernel.
>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Josh Poimboeuf <jpoimboe@kernel.org>
>
> Signed-off-by: Ali Raza <aliraza@bu.edu>
> ---
>  arch/x86/boot/compressed/misc.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index cf690d8712f4..0d07b5661c9c 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -310,6 +310,9 @@ static void parse_elf(void *output)
>  		phdr = &phdrs[i];
> 
>  		switch (phdr->p_type) {
> +#ifdef CONFIG_UNIKERNEL_LINUX
> +		case PT_TLS:
> +#endif

Can you explain why exactly a Linux boot image would have a TLS segment?  What does it do?

>  		case PT_LOAD:
>  #ifdef CONFIG_X86_64
>  			if ((phdr->p_align % 0x200000) != 0)
> -- 
> 2.21.3