No functional changes in this patch.
Updates the comments of _CPU_MP_DATA to delcared that duplications in
CpuMpData are present to avoid to be direct accessed and comprehended
in assembly code. CpuMpData: Intended for use in C code while
ExchangeInfo are used in assembly code in this module.
This patch deletes the unnecessary comments in CpuMpData, since
CpuMpData is no longer responsible for passing information from PEI to
DXE.
Signed-off-by: Yuanhao Xie <yuanhao.xie@intel.com>
Cc: Laszlo Ersek lersek@redhat.com
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
---
UefiCpuPkg/Library/MpInitLib/MpEqu.inc | 2 ++
UefiCpuPkg/Library/MpInitLib/MpLib.h | 13 +++++++------
2 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
index 72af196513..317e627b58 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
+++ b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
@@ -67,6 +67,8 @@ endstruc
;
; Equivalent NASM structure of MP_CPU_EXCHANGE_INFO
+; Assembly routines should refrain from directly interacting with
+; the internal details of CPU_MP_DATA.
;
struc MP_CPU_EXCHANGE_INFO
.StackStart: CTYPE_UINTN 1
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.h b/UefiCpuPkg/Library/MpInitLib/MpLib.h
index af296f6ac0..a96a6389c1 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.h
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.h
@@ -203,6 +203,8 @@ typedef struct _CPU_MP_DATA CPU_MP_DATA;
// MP CPU exchange information for AP reset code
// This structure is required to be packed because fixed field offsets
// into this structure are used in assembly code in this module
+// Assembly routines should refrain from directly interacting with
+// the internal details of CPU_MP_DATA.
//
typedef struct {
UINTN StackStart;
@@ -239,17 +241,16 @@ typedef struct {
#pragma pack()
//
-// CPU MP Data save in memory
+// CPU MP Data save in memory, and intended for use in C code.
+// There are some duplicated fields, such as XD status, between
+// CpuMpData and ExchangeInfo. These duplications in CpuMpData
+// are present to avoid to be direct accessed and comprehended
+// in assembly code.
//
struct _CPU_MP_DATA {
UINT64 CpuInfoInHob;
UINT32 CpuCount;
UINT32 BspNumber;
- //
- // The above fields data will be passed from PEI to DXE
- // Please make sure the fields offset same in the different
- // architecture.
- //
SPIN_LOCK MpLock;
UINTN Buffer;
UINTN CpuApStackSize;
--
2.39.1.windows.1
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-=-=-=-=-=-=-=-=-=-=-=-On 11/21/23 03:35, Yuanhao Xie wrote:
> No functional changes in this patch.
>
> Updates the comments of _CPU_MP_DATA to delcared that duplications in
> CpuMpData are present to avoid to be direct accessed and comprehended
> in assembly code. CpuMpData: Intended for use in C code while
> ExchangeInfo are used in assembly code in this module.
(1) The space characters at the front of these last two lines seem
superfluous.
>
> This patch deletes the unnecessary comments in CpuMpData, since
> CpuMpData is no longer responsible for passing information from PEI to
> DXE.
>
> Signed-off-by: Yuanhao Xie <yuanhao.xie@intel.com>
> Cc: Laszlo Ersek lersek@redhat.com
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> ---
> UefiCpuPkg/Library/MpInitLib/MpEqu.inc | 2 ++
> UefiCpuPkg/Library/MpInitLib/MpLib.h | 13 +++++++------
> 2 files changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
> index 72af196513..317e627b58 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
> +++ b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
> @@ -67,6 +67,8 @@ endstruc
>
> ;
> ; Equivalent NASM structure of MP_CPU_EXCHANGE_INFO
> +; Assembly routines should refrain from directly interacting with
> +; the internal details of CPU_MP_DATA.
> ;
> struc MP_CPU_EXCHANGE_INFO
> .StackStart: CTYPE_UINTN 1
OK!
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.h b/UefiCpuPkg/Library/MpInitLib/MpLib.h
> index af296f6ac0..a96a6389c1 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.h
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.h
> @@ -203,6 +203,8 @@ typedef struct _CPU_MP_DATA CPU_MP_DATA;
> // MP CPU exchange information for AP reset code
> // This structure is required to be packed because fixed field offsets
> // into this structure are used in assembly code in this module
> +// Assembly routines should refrain from directly interacting with
> +// the internal details of CPU_MP_DATA.
> //
> typedef struct {
> UINTN StackStart;
OK!
> @@ -239,17 +241,16 @@ typedef struct {
> #pragma pack()
>
> //
> -// CPU MP Data save in memory
> +// CPU MP Data save in memory, and intended for use in C code.
> +// There are some duplicated fields, such as XD status, between
> +// CpuMpData and ExchangeInfo. These duplications in CpuMpData
> +// are present to avoid to be direct accessed and comprehended
> +// in assembly code.
> //
(2) So, my following comment applies to both the commit message and the
comment here.
I think we should not attempt to explain the *direction* of the
duplications. I think there have been examples for either direction --
at some point, some information was initially only used by the assembly
code, and then needed duplication for the C code's sake; at another
time, duplication in the the opposite direction was necessary (because
stuff used by the C code was needed by the assembly code too).
In particular, the statement "duplicate a field from ExchangeInfo to
CpuMpData so that assembly code need not understand it" seems wrong. For
easing the job of the assembly code, fields would be duplicated in the
*opposite* direction (from CpuMpData to ExchangeInfo).
Note that in patch#1 in this series, we indeed duplicate a field from
ExchangeInfo to CpuMpData -- but there the reason is different: we want
to make the C code's job easier! The "run loop" wait mode does not
involve *rebooting* APs, so there is no assembly code for AP startup,
and no ExchangeInfo either. Therefore, we're making the C code's job
easier, so that it can function with just CpuMpData.
Thus, I would rather avoid any language on the *direction* of
duplication. I'd just say:
MP_CPU_EXCHANGE_INFO is to be consumed by assembly code only, and
CPU_MP_DATA is to be consumed by C code only. If both kinds of code
need to consume a piece of information, then that information must be
duplicated between both structures.
... I'm sorry that I'm splitting hairs for so long on this issue, but I
find this principle behind the duplications *really* non-obvious. So I
would like us to get the documentation right.
(Ray's original explanation was here:
<https://edk2.groups.io/g/devel/message/111336>.)
> struct _CPU_MP_DATA {
> UINT64 CpuInfoInHob;
> UINT32 CpuCount;
> UINT32 BspNumber;
> - //
> - // The above fields data will be passed from PEI to DXE
> - // Please make sure the fields offset same in the different
> - // architecture.
> - //
> SPIN_LOCK MpLock;
> UINTN Buffer;
> UINTN CpuApStackSize;
This is OK.
Thanks!
Laszlo
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