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| author | Vasily Gorbik <gor@linux.ibm.com> | 2022-03-06 22:56:07 +0300 |
|---|---|---|
| committer | Vasily Gorbik <gor@linux.ibm.com> | 2022-03-10 17:58:17 +0300 |
| commit | 1d2ad084800edad81cdc955304272742b10721c7 (patch) | |
| tree | dc6e27260422f6792ffb40a3e7b4d06c7fcf0720 /arch/s390/include/asm/nospec-insn.h | |
| parent | eed38cd2f46f6c4f97c730abd8f23a19db0afbc8 (diff) | |
| download | linux-1d2ad084800edad81cdc955304272742b10721c7.tar.xz | |
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 <iii@linux.ibm.com>
Co-developed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390/include/asm/nospec-insn.h')
| -rw-r--r-- | arch/s390/include/asm/nospec-insn.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/arch/s390/include/asm/nospec-insn.h b/arch/s390/include/asm/nospec-insn.h index 4397eae15e34..bbb5c4d84db9 100644 --- a/arch/s390/include/asm/nospec-insn.h +++ b/arch/s390/include/asm/nospec-insn.h @@ -18,7 +18,11 @@ _LC_BR_R1 = __LC_BR_R1 * the various thunks are merged into a single copy. */ .macro __THUNK_PROLOG_NAME name +#ifdef CONFIG_EXPOLINE_EXTERN + .pushsection .text,"ax",@progbits +#else .pushsection .text.\name,"axG",@progbits,\name,comdat +#endif .globl \name .hidden \name .type \name,@function @@ -115,7 +119,13 @@ _LC_BR_R1 = __LC_BR_R1 555: br \reg .endm +#ifdef CONFIG_EXPOLINE_EXTERN + .macro GEN_BR_THUNK reg,ruse=%r1 + .endm + .macro GEN_BR_THUNK_EXTERN reg,ruse=%r1 +#else .macro GEN_BR_THUNK reg,ruse=%r1 +#endif __DECODE_RR __THUNK_PROLOG_BR,\reg,\ruse __THUNK_EX_BR \reg,\ruse __THUNK_EPILOG |