With CONFIG_PREEMPTION disabled, arch/x86/entry/thunk_64.o is just an
empty object file.
With the newer binutils (tested with 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: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft")
Signed-off-by: Andrea Righi <[email protected]>
---
arch/x86/entry/Makefile | 3 ++-
arch/x86/entry/thunk_32.S | 2 --
arch/x86/entry/thunk_64.S | 4 ----
3 files changed, 2 insertions(+), 7 deletions(-)
diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index 08bf95dbc911..83c98dae74a6 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -21,12 +21,13 @@ CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,)
CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,)
CFLAGS_syscall_x32.o += $(call cc-option,-Wno-override-init,)
-obj-y := entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
+obj-y := 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
diff --git a/arch/x86/entry/thunk_32.S b/arch/x86/entry/thunk_32.S
index f1f96d4d8cd6..5997ec0b4b17 100644
--- a/arch/x86/entry/thunk_32.S
+++ b/arch/x86/entry/thunk_32.S
@@ -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
diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S
index ccd32877a3c4..c7cf79be7231 100644
--- a/arch/x86/entry/thunk_64.S
+++ b/arch/x86/entry/thunk_64.S
@@ -36,14 +36,11 @@ 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(.L_restore)
popq %r11
popq %r10
@@ -58,4 +55,3 @@ SYM_CODE_START_LOCAL_NOALIGN(.L_restore)
ret
_ASM_NOKPROBE(.L_restore)
SYM_CODE_END(.L_restore)
-#endif
--
2.29.2
The following commit has been merged into the x86/entry branch of tip:
Commit-ID: e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
Gitweb: https://git.kernel.org/tip/e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
Author: Andrea Righi <[email protected]>
AuthorDate: Thu, 14 Jan 2021 12:48:35 +01:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Thu, 21 Jan 2021 08:11:52 +01:00
x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
With CONFIG_PREEMPTION disabled, arch/x86/entry/thunk_64.o is just an
empty object file.
With the newer binutils (tested with 2.35.90.20210113-1ubuntu1) the GNU
assembler doesn't generate a symbol table for empty object files and
objtool fails with the following error when a valid symbol table cannot
be found:
arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table
To prevent this from happening, build thunk_$(BITS).o only if
CONFIG_PREEMPTION is enabled.
BugLink: https://bugs.launchpad.net/bugs/1911359
Fixes: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft")
Signed-off-by: Andrea Righi <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Link: https://lore.kernel.org/r/YAAvk0UQelq0Ae7+@xps-13-7390
---
arch/x86/entry/Makefile | 3 ++-
arch/x86/entry/thunk_32.S | 2 --
arch/x86/entry/thunk_64.S | 4 ----
3 files changed, 2 insertions(+), 7 deletions(-)
diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index 08bf95d..83c98da 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -21,12 +21,13 @@ CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,)
CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,)
CFLAGS_syscall_x32.o += $(call cc-option,-Wno-override-init,)
-obj-y := entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
+obj-y := 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
diff --git a/arch/x86/entry/thunk_32.S b/arch/x86/entry/thunk_32.S
index f1f96d4..5997ec0 100644
--- a/arch/x86/entry/thunk_32.S
+++ b/arch/x86/entry/thunk_32.S
@@ -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
diff --git a/arch/x86/entry/thunk_64.S b/arch/x86/entry/thunk_64.S
index 496b11e..9d543c4 100644
--- a/arch/x86/entry/thunk_64.S
+++ b/arch/x86/entry/thunk_64.S
@@ -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
On Thu, Jan 21, 2021 at 09:52:01AM +0100, Andrea Righi wrote:
> On Thu, Jan 21, 2021 at 08:49:28AM +0100, Ingo Molnar wrote:
> >
> > * tip-bot2 for Andrea Righi <[email protected]> wrote:
> >
> > > The following commit has been merged into the x86/entry branch of tip:
> > >
> > > Commit-ID: e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
> > > Gitweb: https://git.kernel.org/tip/e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
> > > Author: Andrea Righi <[email protected]>
> > > AuthorDate: Thu, 14 Jan 2021 12:48:35 +01:00
> > > Committer: Ingo Molnar <[email protected]>
> > > CommitterDate: Thu, 21 Jan 2021 08:11:52 +01:00
> > >
> > > x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
> > >
> > > With CONFIG_PREEMPTION disabled, arch/x86/entry/thunk_64.o is just an
> > > empty object file.
> > >
> > > With the newer binutils (tested with 2.35.90.20210113-1ubuntu1) the GNU
> > > assembler doesn't generate a symbol table for empty object files and
> > > objtool fails with the following error when a valid symbol table cannot
> > > be found:
> > >
> > > arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table
> > >
> > > To prevent this from happening, build thunk_$(BITS).o only if
> > > CONFIG_PREEMPTION is enabled.
> > >
> > > BugLink: https://bugs.launchpad.net/bugs/1911359
> > >
> > > Fixes: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft")
> > > Signed-off-by: Andrea Righi <[email protected]>
> > > Signed-off-by: Ingo Molnar <[email protected]>
> > > Cc: Borislav Petkov <[email protected]>
> > > Link: https://lore.kernel.org/r/YAAvk0UQelq0Ae7+@xps-13-7390
> >
> > Hm, this fails to build on UML defconfig:
> >
> > /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_thunk':
> > /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:34: undefined reference to `preempt_schedule'
> > /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_notrace_thunk':
> > /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:35: undefined reference to `preempt_schedule_notrace'
> >
> > Thanks,
> >
> > Ingo
>
> I've been able to reproduce it, I'm looking at this right now. Thanks!
I see, basically UML selects ARCH_NO_PREEMPT, but in
arch/x86/um/Makefile it explicitly includes thunk_$(BITS).o regardless.
Considering that thunk_$(BITS) only contains preemption code now, we can
probably drop it from the Makefile, or, to be more consistent with the
x86 change, we could include it only if CONFIG_PREEMPTION is enabled
(even if it would never be, because UML has ARCH_NO_PREEMPT).
If it's unlikely that preemption will be enabled in UML one day I'd
probably go with the former, otherwise I'd go with the latter, because
it looks more consistent.
Opinions?
Thanks,
-Andrea
On Thu, Jan 21, 2021 at 08:49:28AM +0100, Ingo Molnar wrote:
>
> * tip-bot2 for Andrea Righi <[email protected]> wrote:
>
> > The following commit has been merged into the x86/entry branch of tip:
> >
> > Commit-ID: e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
> > Gitweb: https://git.kernel.org/tip/e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
> > Author: Andrea Righi <[email protected]>
> > AuthorDate: Thu, 14 Jan 2021 12:48:35 +01:00
> > Committer: Ingo Molnar <[email protected]>
> > CommitterDate: Thu, 21 Jan 2021 08:11:52 +01:00
> >
> > x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
> >
> > With CONFIG_PREEMPTION disabled, arch/x86/entry/thunk_64.o is just an
> > empty object file.
> >
> > With the newer binutils (tested with 2.35.90.20210113-1ubuntu1) the GNU
> > assembler doesn't generate a symbol table for empty object files and
> > objtool fails with the following error when a valid symbol table cannot
> > be found:
> >
> > arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table
> >
> > To prevent this from happening, build thunk_$(BITS).o only if
> > CONFIG_PREEMPTION is enabled.
> >
> > BugLink: https://bugs.launchpad.net/bugs/1911359
> >
> > Fixes: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft")
> > Signed-off-by: Andrea Righi <[email protected]>
> > Signed-off-by: Ingo Molnar <[email protected]>
> > Cc: Borislav Petkov <[email protected]>
> > Link: https://lore.kernel.org/r/YAAvk0UQelq0Ae7+@xps-13-7390
>
> Hm, this fails to build on UML defconfig:
>
> /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_thunk':
> /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:34: undefined reference to `preempt_schedule'
> /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_notrace_thunk':
> /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:35: undefined reference to `preempt_schedule_notrace'
>
> Thanks,
>
> Ingo
I've been able to reproduce it, I'm looking at this right now. Thanks!
-Andrea
* tip-bot2 for Andrea Righi <[email protected]> wrote:
> The following commit has been merged into the x86/entry branch of tip:
>
> Commit-ID: e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
> Gitweb: https://git.kernel.org/tip/e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89
> Author: Andrea Righi <[email protected]>
> AuthorDate: Thu, 14 Jan 2021 12:48:35 +01:00
> Committer: Ingo Molnar <[email protected]>
> CommitterDate: Thu, 21 Jan 2021 08:11:52 +01:00
>
> x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
>
> With CONFIG_PREEMPTION disabled, arch/x86/entry/thunk_64.o is just an
> empty object file.
>
> With the newer binutils (tested with 2.35.90.20210113-1ubuntu1) the GNU
> assembler doesn't generate a symbol table for empty object files and
> objtool fails with the following error when a valid symbol table cannot
> be found:
>
> arch/x86/entry/thunk_64.o: warning: objtool: missing symbol table
>
> To prevent this from happening, build thunk_$(BITS).o only if
> CONFIG_PREEMPTION is enabled.
>
> BugLink: https://bugs.launchpad.net/bugs/1911359
>
> Fixes: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft")
> Signed-off-by: Andrea Righi <[email protected]>
> Signed-off-by: Ingo Molnar <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Link: https://lore.kernel.org/r/YAAvk0UQelq0Ae7+@xps-13-7390
Hm, this fails to build on UML defconfig:
/home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_thunk':
/home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:34: undefined reference to `preempt_schedule'
/home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_notrace_thunk':
/home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:35: undefined reference to `preempt_schedule_notrace'
Thanks,
Ingo