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Subject[tip: x86/core] x86: Annotate call_on_stack()
The following commit has been merged into the x86/core branch of tip:

Commit-ID: 2170221418e44b3c3d0171194915156db31aebc1
Gitweb: https://git.kernel.org/tip/2170221418e44b3c3d0171194915156db31aebc1
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 08 Mar 2022 16:30:50 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Mar 2022 23:53:37 +01:00

x86: Annotate call_on_stack()

vmlinux.o: warning: objtool: page_fault_oops()+0x13c: unreachable instruction

0000 000000000005b460 <page_fault_oops>:
...
0128 5b588: 49 89 23 mov %rsp,(%r11)
012b 5b58b: 4c 89 dc mov %r11,%rsp
012e 5b58e: 4c 89 f2 mov %r14,%rdx
0131 5b591: 48 89 ee mov %rbp,%rsi
0134 5b594: 4c 89 e7 mov %r12,%rdi
0137 5b597: e8 00 00 00 00 call 5b59c <page_fault_oops+0x13c> 5b598: R_X86_64_PLT32 handle_stack_overflow-0x4
013c 5b59c: 5c pop %rsp

vmlinux.o: warning: objtool: sysvec_reboot()+0x6d: unreachable instruction

0000 00000000000033f0 <sysvec_reboot>:
...
005d 344d: 4c 89 dc mov %r11,%rsp
0060 3450: e8 00 00 00 00 call 3455 <sysvec_reboot+0x65> 3451: R_X86_64_PLT32 irq_enter_rcu-0x4
0065 3455: 48 89 ef mov %rbp,%rdi
0068 3458: e8 00 00 00 00 call 345d <sysvec_reboot+0x6d> 3459: R_X86_64_PC32 .text+0x47d0c
006d 345d: e8 00 00 00 00 call 3462 <sysvec_reboot+0x72> 345e: R_X86_64_PLT32 irq_exit_rcu-0x4
0072 3462: 5c pop %rsp

Both cases are due to a call_on_stack() calling a __noreturn function.
Since that's an inline asm, GCC can't do anything about the
instructions after the CALL. Therefore put in an explicit
ASM_REACHABLE annotation to make sure objtool and gcc are consistently
confused about control flow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.468805622@infradead.org
---
arch/x86/include/asm/irq_stack.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/irq_stack.h b/arch/x86/include/asm/irq_stack.h
index ae9d40f..05af249 100644
--- a/arch/x86/include/asm/irq_stack.h
+++ b/arch/x86/include/asm/irq_stack.h
@@ -99,7 +99,8 @@
}

#define ASM_CALL_ARG0 \
- "call %P[__func] \n"
+ "call %P[__func] \n" \
+ ASM_REACHABLE

#define ASM_CALL_ARG1 \
"movq %[arg1], %%rdi \n" \
\
 
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