Re: [tip: x86/entry] x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
* tip-bot2 for Andrea Righi wrote: > The following commit has been merged into the x86/entry branch of tip: > > Commit-ID: e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89 > Gitweb: > https://git.kernel.org/tip/e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89 > Author:Andrea Righi > AuthorDate:Thu, 14 Jan 2021 12:48:35 +01:00 > Committer: Ingo Molnar > CommitterDate: Thu, 21 Jan 2021 08:11:52 +01:00 > > x86/entry: Build thunk_$(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_$(BITS).o only if > CONFIG_PREEMPTION is enabled. > > BugLink: https://bugs.launchpad.net/bugs/1911359 > > Fixes: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft") > Signed-off-by: Andrea Righi > Signed-off-by: Ingo Molnar > Cc: Borislav Petkov > Link: https://lore.kernel.org/r/YAAvk0UQelq0Ae7+@xps-13-7390 Hm, this fails to build on UML defconfig: /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_thunk': /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:34: undefined reference to `preempt_schedule' /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_notrace_thunk': /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:35: undefined reference to `preempt_schedule_notrace' Thanks, Ingo
Re: [tip: x86/entry] x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
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 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 > > > AuthorDate:Thu, 14 Jan 2021 12:48:35 +01:00 > > > Committer: Ingo Molnar > > > 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 > > > Signed-off-by: Ingo Molnar > > > Cc: Borislav Petkov > > > 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
Re: [tip: x86/entry] x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
On Thu, Jan 21, 2021 at 08:49:28AM +0100, Ingo Molnar wrote: > > * tip-bot2 for Andrea Righi wrote: > > > The following commit has been merged into the x86/entry branch of tip: > > > > Commit-ID: e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89 > > Gitweb: > > https://git.kernel.org/tip/e6d92b6680371ae1aeeb6c5eb2387fdc5d9a2c89 > > Author:Andrea Righi > > AuthorDate:Thu, 14 Jan 2021 12:48:35 +01:00 > > Committer: Ingo Molnar > > CommitterDate: Thu, 21 Jan 2021 08:11:52 +01:00 > > > > x86/entry: Build thunk_$(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_$(BITS).o only if > > CONFIG_PREEMPTION is enabled. > > > > BugLink: https://bugs.launchpad.net/bugs/1911359 > > > > Fixes: 320100a5ffe5 ("x86/entry: Remove the TRACE_IRQS cruft") > > Signed-off-by: Andrea Righi > > Signed-off-by: Ingo Molnar > > Cc: Borislav Petkov > > Link: https://lore.kernel.org/r/YAAvk0UQelq0Ae7+@xps-13-7390 > > Hm, this fails to build on UML defconfig: > > > /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: > arch/x86/um/../entry/thunk_64.o: in function `preempt_schedule_thunk': > /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:34: undefined > reference to `preempt_schedule' > > /home/mingo/gcc/cross/lib/gcc/x86_64-linux/9.3.1/../../../../x86_64-linux/bin/ld: > arch/x86/um/../entry/thunk_64.o: in function > `preempt_schedule_notrace_thunk': > /home/mingo/tip.cross/arch/x86/um/../entry/thunk_64.S:35: undefined > reference to `preempt_schedule_notrace' > > Thanks, > > Ingo I've been able to reproduce it, I'm looking at this right now. Thanks! -Andrea
[tip: x86/entry] x86/entry: Build thunk_$(BITS) only if CONFIG_PREEMPTION=y
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 AuthorDate:Thu, 14 Jan 2021 12:48:35 +01:00 Committer: Ingo Molnar 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 Signed-off-by: Ingo Molnar Cc: Borislav Petkov 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