From 1d2ad084800edad81cdc955304272742b10721c7 Mon Sep 17 00:00:00 2001 From: Vasily Gorbik Date: Sun, 6 Mar 2022 20:56:07 +0100 Subject: s390/nospec: add an option to use thunk-extern Currently with -mindirect-branch=thunk and -mfunction-return=thunk compiler options expoline thunks are put into individual COMDAT group sections. s390 is the only architecture which has group sections and it has implications for kpatch and objtool tools support. Using -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern is an alternative, which comes with a need to generate all required expoline thunks manually. Unfortunately modules area is too far away from the kernel image, and expolines from the kernel image cannon be used. But since all new distributions (except Debian) build kernels for machine generations newer than z10, where "exrl" instruction is available, that leaves only 16 expolines thunks possible. Provide an option to build the kernel with -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern for z10 or newer. This also requires to postlink expoline thunks into all modules explicitly. Currently modules already contain most expolines anyhow. Unfortunately -mindirect-branch=thunk-extern and -mfunction-return=thunk-extern options support is broken in gcc <= 11.2. Additional compile test is required to verify proper gcc support. Acked-by: Ilya Leoshkevich Co-developed-by: Sumanth Korikkar Signed-off-by: Sumanth Korikkar Signed-off-by: Vasily Gorbik --- arch/s390/tools/gcc-thunk-extern.sh | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) create mode 100755 arch/s390/tools/gcc-thunk-extern.sh (limited to 'arch/s390/tools') diff --git a/arch/s390/tools/gcc-thunk-extern.sh b/arch/s390/tools/gcc-thunk-extern.sh new file mode 100755 index 000000000000..20bcbf6dd7ab --- /dev/null +++ b/arch/s390/tools/gcc-thunk-extern.sh @@ -0,0 +1,24 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# Borrowed from gcc: gcc/testsuite/gcc.target/s390/nobp-section-type-conflict.c +# Checks that we don't get error: section type conflict with ‘put_page’. + +cat << "END" | $@ -x c - -fno-PIE -march=z10 -mindirect-branch=thunk-extern -mfunction-return=thunk-extern -mindirect-branch-table -O2 -c -o /dev/null +int a; +int b (void); +void c (int); + +static void +put_page (void) +{ + if (b ()) + c (a); +} + +__attribute__ ((__section__ (".init.text"), __cold__)) void +d (void) +{ + put_page (); + put_page (); +} +END -- cgit v1.2.3