On Mon, Feb 25, 2019 at 02:21:03PM +0100, Peter Zijlstra wrote: > On Mon, Feb 25, 2019 at 12:47:00AM -0800, h...@zytor.com wrote: > > It doesn't have to understand the contents of the memop, but it seems > > that the presence of a modrm with mode ≠ 3 should be plenty. It needs > > to know that much in order to know the length of instructions anyway. > > For extra credit, ignore LEA or hinting instructions. > > A little something like so then?
$ ./objtool check --no-fp --backtrace ../../defconfig-build/arch/x86/lib/usercopy_64.o ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: .altinstr_replacement+0x3: UACCESS disable without MEMOPs: __clear_user() ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: __clear_user()+0x3a: (alt) ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: __clear_user()+0x2e: (branch) ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: __clear_user()+0x18: (branch) ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: .altinstr_replacement+0xffffffffffffffff: (branch) ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: __clear_user()+0x5: (alt) ../../defconfig-build/arch/x86/lib/usercopy_64.o: warning: objtool: __clear_user()+0x0: <=== (func) 0000000000000000 <__clear_user>: 0: e8 00 00 00 00 callq 5 <__clear_user+0x5> 1: R_X86_64_PLT32 __fentry__-0x4 5: 90 nop 6: 90 nop 7: 90 nop 8: 48 89 f0 mov %rsi,%rax b: 48 c1 ee 03 shr $0x3,%rsi f: 83 e0 07 and $0x7,%eax 12: 48 89 f1 mov %rsi,%rcx 15: 48 85 c9 test %rcx,%rcx 18: 74 0f je 29 <__clear_user+0x29> 1a: 48 c7 07 00 00 00 00 movq $0x0,(%rdi) 21: 48 83 c7 08 add $0x8,%rdi 25: ff c9 dec %ecx 27: 75 f1 jne 1a <__clear_user+0x1a> 29: 48 89 c1 mov %rax,%rcx 2c: 85 c9 test %ecx,%ecx 2e: 74 0a je 3a <__clear_user+0x3a> 30: c6 07 00 movb $0x0,(%rdi) 33: 48 ff c7 inc %rdi 36: ff c9 dec %ecx 38: 75 f6 jne 30 <__clear_user+0x30> 3a: 90 nop 3b: 90 nop 3c: 90 nop 3d: 48 89 c8 mov %rcx,%rax 40: c3 retq Seems correct. Not sure you want to go fix that though. Let me know if you want more output.
