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x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y

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[ Upstream commit de979c8357 ]

With CONFIG_PREEMPTION disabled, arch/x86/entry/thunk_$(BITS).o becomes
an empty object file.

With some old versions of binutils (i.e., 2.35.90.20210113-1ubuntu1) the
GNU assembler doesn't generate a symbol table for empty object files and
objtool fails with the following error when a valid symbol table cannot
be found:

  arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table

To prevent this from happening, build thunk_$(BITS).o only if
CONFIG_PREEMPTION is enabled.

BugLink: https://bugs.launchpad.net/bugs/1911359

Fixes: 320100a5ff ("x86/entry: Remove the TRACE_IRQS cruft")
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/Ys/Ke7EWjcX+ZlXO@arighi-desktop
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Andrea Righi 2022-07-14 09:49:15 +02:00 • committed by Justin Hammond
parent 83b0b26a19
commit b102bcda07
4 changed files with 4 additions and 8 deletions
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3
arch/x86/entry/Makefile
View file

@ -11,12 +11,13 @@ CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE)
CFLAGS_common.o += -fno-stack-protector
obj-y := entry.o entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
obj-y := entry.o entry_$(BITS).o syscall_$(BITS).o
obj-y += common.o
obj-y += vdso/
obj-y += vsyscall/
obj-$(CONFIG_PREEMPTION) += thunk_$(BITS).o
obj-$(CONFIG_IA32_EMULATION) += entry_64_compat.o syscall_32.o
obj-$(CONFIG_X86_X32_ABI) += syscall_x32.o

2
arch/x86/entry/thunk_32.S
View file

@ -29,10 +29,8 @@ SYM_CODE_START_NOALIGN(\name)
SYM_CODE_END(\name)
.endm
#ifdef CONFIG_PREEMPTION
THUNK preempt_schedule_thunk, preempt_schedule
THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
EXPORT_SYMBOL(preempt_schedule_thunk)
EXPORT_SYMBOL(preempt_schedule_notrace_thunk)
#endif

4
arch/x86/entry/thunk_64.S
View file

@ -31,14 +31,11 @@ SYM_FUNC_END(\name)
_ASM_NOKPROBE(\name)
.endm
#ifdef CONFIG_PREEMPTION
THUNK preempt_schedule_thunk, preempt_schedule
THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
EXPORT_SYMBOL(preempt_schedule_thunk)
EXPORT_SYMBOL(preempt_schedule_notrace_thunk)
#endif
#ifdef CONFIG_PREEMPTION
SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore)
popq %r11
popq %r10
@ -53,4 +50,3 @@ SYM_CODE_START_LOCAL_NOALIGN(__thunk_restore)
RET
_ASM_NOKPROBE(__thunk_restore)
SYM_CODE_END(__thunk_restore)
#endif

3
arch/x86/um/Makefile
View file

@ -28,7 +28,8 @@ else
obj-y += syscalls_64.o vdso/
subarch-y = ../lib/csum-partial_64.o ../lib/memcpy_64.o ../entry/thunk_64.o
subarch-y = ../lib/csum-partial_64.o ../lib/memcpy_64.o
subarch-$(CONFIG_PREEMPTION) += ../entry/thunk_64.o
endif