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

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

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>

Thanks
Laszlo