Ingo Molnar 6ec33db1aa objtool: Fix segfault on unknown alternatives
So 'objtool --link -d vmlinux.o' gets surprised by this endbr64+endbr64 pattern
in ___bpf_prog_run():

	___bpf_prog_run:
	1e7680:  ___bpf_prog_run+0x0                                                     push   %r12
	1e7682:  ___bpf_prog_run+0x2                                                     mov    %rdi,%r12
	1e7685:  ___bpf_prog_run+0x5                                                     push   %rbp
	1e7686:  ___bpf_prog_run+0x6                                                     xor    %ebp,%ebp
	1e7688:  ___bpf_prog_run+0x8                                                     push   %rbx
	1e7689:  ___bpf_prog_run+0x9                                                     mov    %rsi,%rbx
	1e768c:  ___bpf_prog_run+0xc                                                     movzbl (%rbx),%esi
	1e768f:  ___bpf_prog_run+0xf                                                     movzbl %sil,%edx
	1e7693:  ___bpf_prog_run+0x13                                                    mov    %esi,%eax
	1e7695:  ___bpf_prog_run+0x15                                                    mov    0x0(,%rdx,8),%rdx
	1e769d:  ___bpf_prog_run+0x1d                                                    jmp    0x1e76a2 <__x86_indirect_thunk_rdx>
	1e76a2:  ___bpf_prog_run+0x22                                                    endbr64
	1e76a6:  ___bpf_prog_run+0x26                                                    endbr64
	1e76aa:  ___bpf_prog_run+0x2a                                                    mov    0x4(%rbx),%edx

And crashes due to blindly dereferencing alt->insn->alt_group.

Bail out on NULL ->alt_group, which produces this warning and continues
with the disassembly, instead of a segfault:

  .git/O/vmlinux.o: warning: objtool: <alternative.1e769d>: failed to disassemble alternative

Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2025-12-01 10:42:27 +01:00
2022-09-28 09:02:20 +02:00
2025-02-19 14:53:27 -07:00
2025-11-09 15:10:19 -08:00
2024-03-18 03:36:32 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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