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The following warning is reported when frame pointers and kernel IBT are enabled: vmlinux.o: warning: objtool: ibt_selftest+0x11: sibling call from callable instruction with modified stack frame The problem is that objtool interprets the indirect branch in ibt_selftest() as a sibling call, and GCC inserts a (partial) frame pointer prologue before it: 0000 000000000003f550 <ibt_selftest>: 0000 3f550: f3 0f 1e fa endbr64 0004 3f554: e8 00 00 00 00 call 3f559 <ibt_selftest+0x9> 3f555: R_X86_64_PLT32 __fentry__-0x4 0009 3f559: 55 push %rbp 000a 3f55a: 48 8d 05 02 00 00 00 lea 0x2(%rip),%rax # 3f563 <ibt_selftest_ip> 0011 3f561: ff e0 jmp *%rax Note the inline asm is missing ASM_CALL_CONSTRAINT, so the 'push %rbp' happens before the indirect branch and the 'mov %rsp, %rbp' happens afterwards. Simplify the generated code and make it easier to understand for both tools and humans by moving the selftest to proper asm. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/99a7e16b97bda97bf0a04aa141d6241cd8a839a2.1680912949.git.jpoimboe@kernel.org
17 lines
402 B
ArmAsm
17 lines
402 B
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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#include <linux/linkage.h>
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#include <linux/objtool.h>
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#include <asm/nospec-branch.h>
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SYM_CODE_START(ibt_selftest_noendbr)
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ANNOTATE_NOENDBR
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UNWIND_HINT_FUNC
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/* #CP handler sets %ax to 0 */
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RET
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SYM_CODE_END(ibt_selftest_noendbr)
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SYM_FUNC_START(ibt_selftest)
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lea ibt_selftest_noendbr(%rip), %rax
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ANNOTATE_RETPOLINE_SAFE
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jmp *%rax
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SYM_FUNC_END(ibt_selftest)
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