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Subject[PATCH v6 16/27] compiler: Option to add PROVIDE_HIDDEN replacement for weak symbols
Date
Provide an option to have a PROVIDE_HIDDEN (linker script) entry for
each weak symbol. This option solves an error in x86_64 where the linker
optimizes PIE generated code to be non-PIE because --emit-relocs was used
instead of -pie (to reduce dynamic relocations).

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

diff --git a/init/Kconfig b/init/Kconfig
index 116e0de4817f..2261c9891631 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2104,6 +2104,13 @@ 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 bc7f1fc1f55b..abf44a804c79 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -119,6 +119,17 @@ 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()
@@ -200,6 +211,9 @@ 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
--
2.20.1.495.gaa96b0ce6b-goog
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