linux-kernel - Re: [PATCH v5 01/12] modpost: split the section mismatch checks into section-check.c

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Message-ID: <CAKwvOdkMqyssbZ9imYM8Re+NL4U1K2tYj37_1XUtmjj8LSt5GQ@mail.gmail.com>
Date:   Wed, 11 May 2022 15:31:08 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-modules@...r.kernel.org, llvm@...ts.linux.dev,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH v5 01/12] modpost: split the section mismatch checks into section-check.c

On Wed, May 11, 2022 at 9:49 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> -/* sections that we do not want to do full section mismatch check on */
> -static const char *const section_white_list[] =
> -{
> -       ".comment*",
> -       ".debug*",
> -       ".cranges",             /* sh64 */
> -       ".zdebug*",             /* Compressed debug sections. */
> -       ".GCC.command.line",    /* record-gcc-switches */
> -       ".mdebug*",        /* alpha, score, mips etc. */
> -       ".pdr",            /* alpha, score, mips etc. */
> -       ".stab*",
> -       ".note*",
> -       ".got*",
> -       ".toc*",
> -       ".xt.prop",                              /* xtensa */
> -       ".xt.lit",         /* xtensa */
> -       ".arcextmap*",                  /* arc */
> -       ".gnu.linkonce.arcext*",        /* arc : modules */
> -       ".cmem*",                       /* EZchip */
> -       ".fmt_slot*",                   /* EZchip */
> -       ".gnu.lto*",
> -       ".discard.*",
> -       NULL
> -};


> -/**
> - * Whitelist to allow certain references to pass with no warning.
> - *
> - * Pattern 1:
> - *   If a module parameter is declared __initdata and permissions=0
> - *   then this is legal despite the warning generated.
> - *   We cannot see value of permissions here, so just ignore
> - *   this pattern.
> - *   The pattern is identified by:
> - *   tosec   = .init.data
> - *   fromsec = .data*
> - *   atsym   =__param*
> - *
> - * Pattern 1a:
> - *   module_param_call() ops can refer to __init set function if permissions=0
> - *   The pattern is identified by:
> - *   tosec   = .init.text
> - *   fromsec = .data*
> - *   atsym   = __param_ops_*
> - *
> - * Pattern 2:
> - *   Many drivers utilise a *driver container with references to
> - *   add, remove, probe functions etc.
> - *   the pattern is identified by:
> - *   tosec   = init or exit section
> - *   fromsec = data section
> - *   atsym = *driver, *_template, *_sht, *_ops, *_probe,
> - *           *probe_one, *_console, *_timer
> - *
> - * Pattern 3:
> - *   Whitelist all references from .head.text to any init section
> - *
> - * Pattern 4:
> - *   Some symbols belong to init section but still it is ok to reference
> - *   these from non-init sections as these symbols don't have any memory
> - *   allocated for them and symbol address and value are same. So even
> - *   if init section is freed, its ok to reference those symbols.
> - *   For ex. symbols marking the init section boundaries.
> - *   This pattern is identified by
> - *   refsymname = __init_begin, _sinittext, _einittext
> - *
> - * Pattern 5:
> - *   GCC may optimize static inlines when fed constant arg(s) resulting
> - *   in functions like cpumask_empty() -- generating an associated symbol
> - *   cpumask_empty.constprop.3 that appears in the audit.  If the const that
> - *   is passed in comes from __init, like say nmi_ipi_mask, we get a
> - *   meaningless section warning.  May need to add isra symbols too...
> - *   This pattern is identified by
> - *   tosec   = init section
> - *   fromsec = text section
> - *   refsymname = *.constprop.*
> - *
> - * Pattern 6:
> - *   Hide section mismatch warnings for ELF local symbols.  The goal
> - *   is to eliminate false positive modpost warnings caused by
> - *   compiler-generated ELF local symbol names such as ".LANCHOR1".
> - *   Autogenerated symbol names bypass modpost's "Pattern 2"
> - *   whitelisting, which relies on pattern-matching against symbol
> - *   names to work.  (One situation where gcc can autogenerate ELF
> - *   local symbols is when "-fsection-anchors" is used.)
> - **/

Losing the ability to git blame (from the top level) the above lines
does cause me grief and mental anguish though. It's not gone, just
buried a bit deeper.
-- 
Thanks,
~Nick Desaulniers