[PATCH v2 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols

From: Thomas Garnier <thgarnie@google.com>
To: Herbert Xu <herbert@gondor.apana.org.au>,
	"David S . Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	Thomas Garnier <thgarnie@google.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	Kees Cook <keescook@chromium.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dominik Brodowski <linux@dominikbrodowski.net>,
	Borislav Petkov <bp@alien8.de>, Borislav Petkov <bp@suse.de>,
	"Raf
Cc: linux-arch@vger.kernel.org, kvm@vger.kernel.org,
	linux-pm@vger.kernel.org, x86@kernel.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	linux-sparse@vger.kernel.org, linux-crypto@vger.kernel.org,
	kernel-hardening@lists.openwall.com,
	xen-devel@lists.xenproject.org
Subject: [PATCH v2 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols
Date: Tue, 13 Mar 2018 13:59:34 -0700	[thread overview]
Message-ID: <20180313205945.245105-17-thgarnie@google.com> (raw)
In-Reply-To: <20180313205945.245105-1-thgarnie@google.com>

Provide an option to have a PROVIDE_HIDDEN (linker script) entry for
each weak symbol. This option solve an error in x86_64 where the linker
optimizes pie generate code to be non-pie because --emit-relocs was used
instead of -pie (to reduce dynamic relocations).

Signed-off-by: Thomas Garnier <thgarnie@google.com>
---
 init/Kconfig            |  7 +++++++
 scripts/link-vmlinux.sh | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index c924babc6d47..fe9f9ada4db0 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1927,6 +1927,13 @@ config ASN1
 	  inform it as to what tags are to be expected in a stream and what
 	  functions to call on what tags.
 
+config WEAK_PROVIDE_HIDDEN
+	bool
+	help
+	  Generate linker script PROVIDE_HIDDEN entries for all weak symbols. It
+	  allows to prevent non-pie code being replaced by the linker if the
+	  emit-relocs option is used instead of pie (useful for x86_64 pie).
+
 source "kernel/Kconfig.locks"
 
 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 08ca08e9105c..c015f5142ecf 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -146,6 +146,17 @@ kallsyms()
 	${CC} ${aflags} -c -o ${2} ${afile}
 }
 
+gen_weak_provide_hidden()
+{
+        if [ -n "${CONFIG_WEAK_PROVIDE_HIDDEN}" ]; then
+                local pattern="s/^\s\+ w \(\w\+\)$/PROVIDE_HIDDEN(\1 = .);/gp"
+                echo -e "SECTIONS {\n. = _end;" > .tmp_vmlinux_hiddenld
+                ${NM} ${1} | sed -n "${pattern}" >> .tmp_vmlinux_hiddenld
+                echo "}" >> .tmp_vmlinux_hiddenld
+                LDFLAGS_vmlinux="${LDFLAGS_vmlinux} -T .tmp_vmlinux_hiddenld"
+        fi
+}
+
 # Create map file with all symbols from ${1}
 # See mksymap for additional details
 mksysmap()
@@ -230,6 +241,9 @@ modpost_link vmlinux.o
 # modpost vmlinux.o to check for section mismatches
 ${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o
 
+# Generate weak linker script
+gen_weak_provide_hidden vmlinux.o
+
 kallsymso=""
 kallsyms_vmlinux=""
 if [ -n "${CONFIG_KALLSYMS}" ]; then
-- 
2.16.2.660.g709887971b-goog


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