Re: [PATCH] [RFC] x86: avoid -mtune=atom for objtool warnings

[Arnd Bergmann]

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