[PATCH 6.1 352/473] s390/vdso64: filter out munaligned-symbols flag for vdso

Greg Kroah-Hartman
2024-06-06T14:17:46Z

From: Sumanth Korikkar <sumanthk@linux.ibm.com>

[ Upstream commit 8192a1b3807510d0ed5be1f8988c08f8d41cced9 ]

Gcc recently implemented an optimization [1] for loading symbols without
explicit alignment, aligning with the IBM Z ELF ABI. This ABI mandates
symbols to reside on a 2-byte boundary, enabling the use of the larl
instruction. However, kernel linker scripts may still generate unaligned
symbols. To address this, a new -munaligned-symbols option has been
introduced [2] in recent gcc versions.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2023-June/622872.html
[2] https://gcc.gnu.org/pipermail/gcc-patches/2023-August/625986.html

However, when -munaligned-symbols is used in vdso code, it leads to the
following compilation error:
`.data.rel.ro.local' referenced in section `.text' of
arch/s390/kernel/vdso64/vdso64_generic.o: defined in discarded section
`.data.rel.ro.local' of arch/s390/kernel/vdso64/vdso64_generic.o

vdso linker script discards .data section to make it lightweight.
However, -munaligned-symbols in vdso object files references literal
pool and accesses _vdso_data. Hence, compile vdso code without
-munaligned-symbols. This means in the future, vdso code should deal
with alignment of newly introduced unaligned linker symbols.

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Link: https://lore.kernel.org/r/20240219132734.22881-2-sumanthk@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Stable-dep-of: 10f705253651 ("s390/vdso: Generate unwind information for C modules")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/kernel/vdso64/Makefile | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
index 08e87b083647c..e2e031e4d9243 100644
--- a/arch/s390/kernel/vdso64/Makefile
+++ b/arch/s390/kernel/vdso64/Makefile
@@ -26,6 +26,7 @@ KBUILD_AFLAGS_64 += -m64 -s

KBUILD_CFLAGS_64 := $(filter-out -m64,$(KBUILD_CFLAGS))
KBUILD_CFLAGS_64 := $(filter-out -mno-pic-data-is-text-relative,$(KBUILD_CFLAGS_64))
+KBUILD_CFLAGS_64 := $(filter-out -munaligned-symbols,$(KBUILD_CFLAGS_64))
KBUILD_CFLAGS_64 += -m64 -fPIC -fno-common -fno-builtin
ldflags-y := -shared -soname=linux-vdso64.so.1 \
--hash-style=both --build-id=sha1 -T
--
2.43.0