linux-kernel - Re: [PATCH 5.15 45/76] modpost: Add '.ltext' and '.ltext.*' to TEXT

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Message-ID: <20240313171229.GA3064248@dev-arch.thelio-3990X>
Date: Wed, 13 Mar 2024 10:12:29 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH 5.15 45/76] modpost: Add '.ltext' and '.ltext.*' to
 TEXT_SECTIONS

Hi Sasha,

On Wed, Mar 13, 2024 at 12:41:52PM -0400, Sasha Levin wrote:
> From: Nathan Chancellor <nathan@...nel.org>
> 
> [ Upstream commit 397586506c3da005b9333ce5947ad01e8018a3be ]
> 
> After the linked LLVM change, building ARCH=um defconfig results in a
> segmentation fault in modpost. Prior to commit a23e7584ecf3 ("modpost:
> unify 'sym' and 'to' in default_mismatch_handler()"), there was a
> warning:
> 
>   WARNING: modpost: vmlinux.o(__ex_table+0x88): Section mismatch in reference to the .ltext:(unknown)
>   WARNING: modpost: The relocation at __ex_table+0x88 references
>   section ".ltext" which is not in the list of
>   authorized sections.  If you're adding a new section
>   and/or if this reference is valid, add ".ltext" to the
>   list of authorized sections to jump to on fault.
>   This can be achieved by adding ".ltext" to
>   OTHER_TEXT_SECTIONS in scripts/mod/modpost.c.
> 
> The linked LLVM change moves global objects to the '.ltext' (and
> '.ltext.*' with '-ffunction-sections') sections with '-mcmodel=large',
> which ARCH=um uses. These sections should be handled just as '.text'
> and '.text.*' are, so add them to TEXT_SECTIONS.
> 
> Cc: stable@...r.kernel.org
> Closes: https://github.com/ClangBuiltLinux/linux/issues/1981
> Link: https://github.com/llvm/llvm-project/commit/4bf8a688956a759b7b6b8d94f42d25c13c7af130
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

This causes a warning when building with HOSTCC=clang:

  scripts/mod/modpost.c:1123:37: warning: excess elements in array initializer [-Wexcess-initializers]
   1123 |         .good_tosec = {ALL_TEXT_SECTIONS , NULL},
        |                                            ^~~~
  .../lib/clang/17/include/stddef.h:89:16: note: expanded from macro 'NULL'
     89 | #  define NULL ((void*)0)
        |                ^~~~~~~~~~
  1 warning generated.

Same comment as on the other UML clang-18 patch, I do not think this is
necessary right now in 5.15 and earlier. The other modpost patch can go
as well, as it is only a prerequisite change.

Cheers,
Nathan