Re: [PATCH] UefiCpuPkg/PiSmmCpu: Fix GCC7/GCC8 build failure

["Laszlo Ersek" <lersek@redhat.com>]

On 07/11/19 12:02, Laszlo Ersek wrote:
> Hello Ray,
> 
> On 07/11/19 03:16, Ray Ni wrote:
>> Signed-off-by: Ray Ni <ray.ni@intel.com>
>> Cc: Michael D Kinney <michael.d.kinney@intel.com>
>> Cc: Eric Dong <eric.dong@intel.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> ---
>>  UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
>> index c31160735a..a3b62f7787 100644
>> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
>> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c
>> @@ -571,7 +571,7 @@ ReclaimPages (
>>    //
>>    // First, find the leaf entry has the smallest access record value
>>    //
>> -  for (Pml5Index = 0; Pml5Index < Enable5LevelPaging ? (EFI_PAGE_SIZE / sizeof (*Pml4)) : 1; Pml5Index++) {
>> +  for (Pml5Index = 0; Pml5Index < (Enable5LevelPaging ? (EFI_PAGE_SIZE / sizeof (*Pml4)) : 1); Pml5Index++) {
>>      if ((Pml5[Pml5Index] & IA32_PG_P) == 0 || (Pml5[Pml5Index] & IA32_PG_PMNT) != 0) {
>>        //
>>        // If the PML5 entry is not present or is masked, skip it
>>
> 
> This is not a GCC7/GCC8 build failure, but a genuine bug in the code
> that GCC7/GCC8 helpfully reported.
> 
> The conditional operator ?: has weaker precedence than the relational
> operator <, and so the patch incurs a behavioral change -- thus, it is a
> bugfix.
> 
> If we were only adding the parentheses to reinforce the operator
> bingings that are already in place, i.e., preserving the behavior,
> *then* we could call this a "build failure".
> 
> 
> (1) Please update the subject accordingly, for example:
> 
> UefiCpuPkg/PiSmmCpuDxeSmm: ReclaimPages: fix incorrect operator binding
> 
> (71 characters)
> 
> 
> (2) I'd suggest also adding, to the commit message body:
> 
> Fixes: 7365eb2c8cf1d7112330d09918c0c67e8d0b827a
> 
> With those:
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>

IMPORTANT: please do not push this patch before you revert and reapply
7365eb2c8cf1; otherwise we'll get into a huge mess. Please see here:

https://edk2.groups.io/g/devel/message/43599

(Namely, if you apply this patch on top of 7365eb2c8cf1, then you won't
be able to revert 7365eb2c8cf1, which is a pre-requisite for reverting
7c5010c7f88b.)

Thanks
Laszlo