Date: Thu, 19 Feb 2026 15:20:40 +0000 From: bugzilla-noreply@freebsd.org To: virtualization@FreeBSD.org Subject: [Bug 285853] hv_hid: kernel built with -O0 panics in hv_hid_probe() Message-ID: <bug-285853-27103-aREwFfJvVt@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-285853-27103@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=285853 Zhenlei Huang <zlei@FreeBSD.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |zlei@FreeBSD.org --- Comment #2 from Zhenlei Huang <zlei@FreeBSD.org> --- (In reply to Lexi Winter from comment #0) > (kgdb) disass hv_hid_probe > Dump of assembler code for function hv_hid_probe: > 0xffffffff83d11000 <+0>: add %al,(%rax) > 0xffffffff83d11002 <+2>: add %al,(%rax) > 0xffffffff83d11004 <+4>: add %al,(%rax) > 0xffffffff83d11006 <+6>: add %al,(%rax) > 0xffffffff83d11008 <+8>: add %al,(%rax) > 0xffffffff83d1100a <+10>: add %al,(%rax) Those disassembly looks weird to me. In x86_64 ABI, the rax register is used to stash a return value. Typically a start of a function, say `hv_hid_probe()` in this case, would like to save registers but not firstly operate on rax. The rax, > rax: ffffffff83d11000 rbx: 000019e97c87cf20 rbp: fffffe0092594790 is the address of the function hv_hid_probe(), but `add %al,(%rax)` wants to write 1 byte to (%rax) which is absolutely wrong to me. On loading a module, the linker will set write protecting for .text section, hence you got > fault code = supervisor write data, protection violation which is a runtime exception. My local kernel config is almost identical with yours, ``` zlei@:~/freebsd-src-releng-15.0 % cat sys/amd64/conf/GENERIC-NOOPT # # GENERIC-NOOPT -- disable compiler optimize # include GENERIC ident GENERIC-NOOPT makeoptions COPTFLAGS="-O0 -fno-strict-aliasing" options KSTACK_PAGES=20 ``` And the disassembly looks good to me, ``` zlei@:~ % objdump --disassemble-symbols=hv_hid_probe /usr/obj/usr/home/zlei/freebsd-src-releng-15.0/amd64.amd64/sys/GENERIC-NOOPT/modules/usr/home/zlei/freebsd-src-releng-15.0/sys/modules/hyperv/hid/hv_hid.ko /usr/obj/usr/home/zlei/freebsd-src-releng-15.0/amd64.amd64/sys/GENERIC-NOOPT/modules/usr/home/zlei/freebsd-src-releng-15.0/sys/modules/hyperv/hid/hv_hid.ko: file format elf64-x86-64 Disassembly of section .text: 0000000000000000 <hv_hid_probe>: 0: 55 pushq %rbp 1: 48 89 e5 movq %rsp, %rbp 4: 41 57 pushq %r15 6: 41 56 pushq %r14 8: 53 pushq %rbx 9: 50 pushq %rax a: 48 89 fb movq %rdi, %rbx d: e8 00 00 00 00 callq 0x12 <hv_hid_probe+0x12> 12: 48 89 c7 movq %rax, %rdi 15: 31 f6 xorl %esi, %esi 17: e8 00 00 00 00 callq 0x1c <hv_hid_probe+0x1c> 1c: 41 be 06 00 00 00 movl $0x6, %r14d 22: 85 c0 testl %eax, %eax 24: 75 62 jne 0x88 <hv_hid_probe+0x88> 26: 48 89 df movq %rbx, %rdi 29: e8 00 00 00 00 callq 0x2e <hv_hid_probe+0x2e> 2e: 49 89 c7 movq %rax, %r15 31: 48 8b 08 movq (%rax), %rcx 34: 0f b6 15 00 00 00 00 movzbl (%rip), %edx # 0x3b <hv_hid_probe+0x3b> 3b: 48 8b 04 d1 movq (%rcx,%rdx,8), %rax 3f: 48 81 38 00 00 00 00 cmpq $0x0, (%rax) 46: 74 17 je 0x5f <hv_hid_probe+0x5f> 48: 48 8d 34 d1 leaq (%rcx,%rdx,8), %rsi 4c: 48 8b b9 00 08 00 00 movq 0x800(%rcx), %rdi 53: 48 c7 c2 00 00 00 00 movq $0x0, %rdx 5a: e8 00 00 00 00 callq 0x5f <hv_hid_probe+0x5f> 5f: 4c 89 ff movq %r15, %rdi 62: 48 89 de movq %rbx, %rsi 65: 48 c7 c2 00 00 00 00 movq $0x0, %rdx 6c: ff 50 08 callq *0x8(%rax) 6f: 85 c0 testl %eax, %eax 71: 75 15 jne 0x88 <hv_hid_probe+0x88> 73: 48 89 df movq %rbx, %rdi 76: 48 c7 c6 00 00 00 00 movq $0x0, %rsi 7d: e8 00 00 00 00 callq 0x82 <hv_hid_probe+0x82> 82: 41 be ec ff ff ff movl $0xffffffec, %r14d # imm = 0xFFFFFFEC 88: 44 89 f0 movl %r14d, %eax 8b: 48 83 c4 08 addq $0x8, %rsp 8f: 5b popq %rbx 90: 41 5e popq %r14 92: 41 5f popq %r15 94: 5d popq %rbp 95: c3 retq 96: 66 2e 0f 1f 84 00 00 00 00 00 nopw %cs:(%rax,%rax) ``` Can you please also check the disassembly of the module hv_hid.ko ? -- You are receiving this mail because: You are the assignee for the bug.home | help
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