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    SubjectRe: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings
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    On Tuesday, October 11, 2016 10:51:46 AM CEST Josh Poimboeuf wrote:
    >
    > 3) 0xFC244C03-config:
    > drivers/scsi/fnic/fnic_main.o: warning: objtool: fnic_log_q_error() falls through to next function fnic_handle_link_event()
    > drivers/scsi/snic/snic_res.o: warning: objtool: .text: unexpected end of section
    >
    > These look like another bad gcc bug which is truncating functions:

    Same bug for both of them?

    >
    > 0000000000000940 <snic_log_q_error>:
    > 940: 55 push %rbp
    > 941: 48 89 e5 mov %rsp,%rbp
    > 944: 53 push %rbx
    > 945: 48 89 fb mov %rdi,%rbx
    > 948: e8 00 00 00 00 callq 94d <snic_log_q_error+0xd>
    > 949: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    > 94d: 8b 83 58 02 00 00 mov 0x258(%rbx),%eax
    > 953: 85 c0 test %eax,%eax
    > 955: 75 08 jne 95f <snic_log_q_error+0x1f>
    > 957: e8 00 00 00 00 callq 95c <snic_log_q_error+0x1c>
    > 958: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    > 95c: 5b pop %rbx
    > 95d: 5d pop %rbp
    > 95e: c3 retq
    > 95f: e8 00 00 00 00 callq 964 <snic_log_q_error+0x24>
    > 960: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    > 964: 48 8b 83 10 1c 00 00 mov 0x1c10(%rbx),%rax
    > 96b: 48 8d 78 50 lea 0x50(%rax),%rdi
    > 96f: e8 00 00 00 00 callq 974 <snic_log_q_error+0x34>
    > 970: R_X86_64_PC32 ioread32-0x4
    > 974: 83 bb 58 02 00 00 01 cmpl $0x1,0x258(%rbx)
    > 97b: 76 da jbe 957 <snic_log_q_error+0x17>
    > 97d: e8 00 00 00 00 callq 982 <snic_log_q_error+0x42>
    > 97e: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    >
    > [end of file]
    >
    > Notice how it just falls off the end of the function. We had a similar
    > bug before:
    >
    > https://lkml.kernel.org/r/20160413033649.7r3msnmo3trtq47z@treble

    I remember that nightmare :(

    > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
    >
    > I'm not sure yet if this is the same gcc bug or a different one. Maybe
    > it's related to the new GCC_PLUGIN_SANCOV?

    I've reduced one of the test cases to this now:

    /* gcc-6 -O2 -fno-strict-aliasing -fno-reorder-blocks -fno-omit-frame-pointer -Wno-pointer-sign -fsanitize-coverage=trace-pc -Wall -Werror -c snic_res.c -o snic_res.o */
    typedef int spinlock_t;
    extern unsigned int ioread32(void *);
    struct vnic_wq_ctrl {
    unsigned int error_status;
    };
    struct vnic_wq {
    struct vnic_wq_ctrl *ctrl;
    } mempool_t;
    struct snic {
    unsigned int wq_count;
    __attribute__ ((__aligned__)) struct vnic_wq wq[1];
    spinlock_t wq_lock[1];
    };
    unsigned int snic_log_q_error_err_status;
    void snic_log_q_error(struct snic *snic)
    {
    unsigned int i;
    for (i = 0; i < snic->wq_count; i++)
    snic_log_q_error_err_status =
    ioread32(&snic->wq[i].ctrl->error_status);
    }

    which gets compiled into

    0000000000000000 <snic_log_q_error>:
    0: 55 push %rbp
    1: 48 89 e5 mov %rsp,%rbp
    4: 53 push %rbx
    5: 48 89 fb mov %rdi,%rbx
    8: 48 83 ec 08 sub $0x8,%rsp
    c: e8 00 00 00 00 callq 11 <snic_log_q_error+0x11>
    d: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    11: 8b 03 mov (%rbx),%eax
    13: 85 c0 test %eax,%eax
    15: 75 11 jne 28 <snic_log_q_error+0x28>
    17: 48 83 c4 08 add $0x8,%rsp
    1b: 5b pop %rbx
    1c: 5d pop %rbp
    1d: e9 00 00 00 00 jmpq 22 <snic_log_q_error+0x22>
    1e: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    22: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1)
    28: e8 00 00 00 00 callq 2d <snic_log_q_error+0x2d>
    29: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4
    2d: 48 8b 7b 10 mov 0x10(%rbx),%rdi
    31: e8 00 00 00 00 callq 36 <snic_log_q_error+0x36>
    32: R_X86_64_PC32 ioread32-0x4
    36: 89 05 00 00 00 00 mov %eax,0x0(%rip) # 3c <snic_log_q_error+0x3c>
    38: R_X86_64_PC32 snic_log_q_error_err_status-0x4
    3c: 83 3b 01 cmpl $0x1,(%rbx)
    3f: 76 d6 jbe 17 <snic_log_q_error+0x17>
    41: e8 00 00 00 00 callq 46 <snic_log_q_error+0x46>
    42: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4

    Arnd

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