Re: [dpdk-dev] [PATCH] i40e: fix shared code compile warning

["Chen, Jing D" <jing.d.chen@intel.com>]

Hi Thomas,

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Tuesday, June 24, 2014 6:06 PM
> To: Chen, Jing D
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] i40e: fix shared code compile warning
> 
> 2014-06-24 09:47, Chen, Jing D:
> > From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > > 2014-06-24 13:22, Chen Jing D:
> > > > +CFLAGS_i40e_lan_hmc.o += -Wno-error
> > >
> > > I know we shouldn't modify base drivers. But this one seems to be an
> > > important error. In such case, we already modified base driver. Recently:
> > > http://dpdk.org/ml/archives/dev/2014-June/003498.html
> >
> > I think it's different. The logic is right after adding the patch.
> > Below is my finding.
> 
> > In this case, it met the error when compile on 32-bits OS. The message is :
> >
> >
> /jenkins/workspace/DPDK_AUTO_IDT_VM_RHEL65_32_BUILD/DPDK/lib/libr
> te_pm
> > d_i40e
> > /i40e/i40e_lan_hmc.c: In function ‘i40e_write_qword’:
> >
> /jenkins/workspace/DPDK_AUTO_IDT_VM_RHEL65_32_BUILD/DPDK/lib/libr
> te_pm
> > d_i40
> > e/i40e/i40e_lan_hmc.c:917: error: integer constant is too large for ‘long’
> > type
> >
> /jenkins/workspace/DPDK_AUTO_IDT_VM_RHEL65_32_BUILD/DPDK/lib/libr
> te_pm
> > d_i40
> > e/i40e/i40e_lan_hmc.c: In function ‘i40e_read_qword’:
> >
> /jenkins/workspace/DPDK_AUTO_IDT_VM_RHEL65_32_BUILD/DPDK/lib/libr
> te_pm
> > d_i40
> > e/i40e/i40e_lan_hmc.c:1097: error: integer constant is too large for ‘long’
> > type
> > I found the code that cause errors. 'mask' is 'uint64_t' type and is
> > assigned to value 0Xffff_ffff_ffff_ffff. Compiler assumes the constant
> > is 'int' type by default. If changed it to oxffff_ffff_ffff_ffffULL,
> > the warning will be gone.
> 
> > 	if (ce_info->width < 64)
> > 		mask = ((u64)1 << ce_info->width) - 1;
> > 	else
> > 		mask = 0xFFFFFFFFFFFFFFFF;
> >
> > besides that, I dis-assembler the code with the patch and get below
> segment.
> > It seems right.
> 
> >         if (ce_info->width < 64)
> >     1946:       8b 45 0c                mov    0xc(%ebp),%eax
> >     1949:       0f b7 40 04             movzwl 0x4(%eax),%eax
> >     194d:       66 83 f8 3f             cmp    $0x3f,%ax
> >     1951:       77 30                   ja     1983 <i40e_write_qword+0x62>
> > mask = ((u64)1 << ce_info->width) - 1;
> >     1953:       8b 45 0c                mov    0xc(%ebp),%eax
> >     1956:       0f b7 40 04             movzwl 0x4(%eax),%eax
> >     195a:       0f b7 c8                movzwl %ax,%ecx
> >     195d:       b8 01 00 00 00          mov    $0x1,%eax
> >     1962:       ba 00 00 00 00          mov    $0x0,%edx
> >     1967:       0f a5 c2                shld   %cl,%eax,%edx
> >     196a:       d3 e0                   shl    %cl,%eax
> >     196c:       f6 c1 20                test   $0x20,%cl
> >     196f:       74 04                   je     1975 <i40e_write_qword+0x54>
> > 1971:       89 c2                   mov    %eax,%edx
> >     1973:       31 c0                   xor    %eax,%eax
> >     1975:       83 c0 ff                add    $0xffffffff,%eax
> >     1978:       83 d2 ff                adc    $0xffffffff,%edx
> >     197b:       89 45 e0                mov    %eax,-0x20(%ebp)
> >     197e:       89 55 e4                mov    %edx,-0x1c(%ebp)
> >     1981:       eb 0e                   jmp    1991 <i40e_write_qword+0x70>
> > else
> >                 mask = 0xFFFFFFFFFFFFFFFF;
> >     1983:       c7 45 e0 ff ff ff ff    movl   $0xffffffff,-0x20(%ebp)
> >     198a:       c7 45 e4 ff ff ff ff    movl   $0xffffffff,-0x1c(%ebp)
> 
> Maybe I don't understand. You are saying you can fix the compiler warning
> by adding ULL to the constant. This is a simple patch and is a lot nicer than
> 	CFLAGS_i40e_lan_hmc.o += -Wno-error
> Even if the asm code seems right, it would be more secure to remove this
> warning.
> 
> PS: please try to configure your mailer to add citation marks.
> 
> --
> Thomas
[Chen, Jing D] 

Generally speaking, I can fix the compile error by 2 ways.
1. change shared code with "ULL" suffix, which means that we had to maintain it. In any time shared code updates, 
    we needs to find out what change we've made in history and compare with new shared code.  
    I don’t know who should be responsible for that and how we record the changes. If you have good idea,
    please share with me. 
2. my committed patch to ignore the warning on that file and continue the compile .  By doing so, the logic is right and 
   didn't change code's behavior.  We also needn't maintain it.  Even in bad case we find bugs hidden behind the 
    '--CFLAGS_i40e_lan_hmc.0' warning in future, we can fix it after bug occurred. That's simple.