linux-kernel - [PATCH v9 06/16] kbuild: lto: add a default list of used symbols

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Message-Id: <20201211184633.3213045-7-samitolvanen@google.com>
Date:   Fri, 11 Dec 2020 10:46:23 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v9 06/16] kbuild: lto: add a default list of used symbols

With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a
binary when the .mod files are generated, which means they don't yet
contain references to certain symbols that will be present in the final
binaries. This includes intrinsic functions, such as memcpy, memmove,
and memset [1], and stack protector symbols [2]. This change adds a
default symbol list to use with CONFIG_TRIM_UNUSED_KSYMS when Clang's
LTO is used.

[1] https://llvm.org/docs/LangRef.html#standard-c-c-library-intrinsics
[2] https://llvm.org/docs/LangRef.html#llvm-stackprotector-intrinsic

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 init/Kconfig                | 1 +
 scripts/lto-used-symbollist | 5 +++++
 2 files changed, 6 insertions(+)
 create mode 100644 scripts/lto-used-symbollist

diff --git a/init/Kconfig b/init/Kconfig
index 0872a5a2e759..e88c919c1bf1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2297,6 +2297,7 @@ config TRIM_UNUSED_KSYMS
 config UNUSED_KSYMS_WHITELIST
 	string "Whitelist of symbols to keep in ksymtab"
 	depends on TRIM_UNUSED_KSYMS
+	default "scripts/lto-used-symbollist" if LTO_CLANG
 	help
 	  By default, all unused exported symbols will be un-exported from the
 	  build when TRIM_UNUSED_KSYMS is selected.
diff --git a/scripts/lto-used-symbollist b/scripts/lto-used-symbollist
new file mode 100644
index 000000000000..38e7bb9ebaae
--- /dev/null
+++ b/scripts/lto-used-symbollist
@@ -0,0 +1,5 @@
+memcpy
+memmove
+memset
+__stack_chk_fail
+__stack_chk_guard
-- 
2.29.2.576.ga3fc446d84-goog