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* [PATCH v2 0/1] Refine casting expression result to bigger size
@ 2017-01-24  7:25 Hao Wu
  2017-01-24  7:25 ` [PATCH v2 1/1] MdePkg: " Hao Wu
  0 siblings, 1 reply; 7+ messages in thread
From: Hao Wu @ 2017-01-24  7:25 UTC (permalink / raw)
  To: edk2-devel
  Cc: Hao Wu, Michael Kinney, Liming Gao, Eric Dong, Laszlo Ersek,
	Ard Biesheuvel

Please note that this patch is maily for feedback collection and the patch
only covers MdePkg. We are working on patches for other packages.


V2:
Follow the below rules to refine codes:
1). When the expression will not overflow within the rank of "int", remove
the explicit type casts:
c = a + b;

2). When the expression is possible to overflow the range of unsigned int/
int:
c = (UINT64)a + b;

V1:
There are cases that the operands of an expression are all with rank less
than UINT64/INT64 and the result of the expression is casted to
UINT64/INT64 to fit the target size.

An example will be:
UINT32 a,b;
// a and b can be any unsigned int type with rank less than UINT64, like
// UINT8, UINT16, etc.
UINT64 c;
c = (UINT64) (a + b);

Some static code checkers may warn that the expression result might
overflow within the rank of int (integer promotions) and the result is
then cast to a bigger size.

For the consideration of generated binaries size, the commit will keep the
size of the operands as the size of int, and explitly add a type cast
before converting the result to UINT64/INT64.

1). When there is no operand with type UINTN
(UINTN)  (a + b) -> (UINTN)(UINT32)  (a + b) or
(UINT64) (a + b) -> (UINT64)(UINT32) (a + b)

2). Otherwise
(UINT64) (a + b) -> (UINT64)(UINTN)  (a + b)

Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Hao Wu (1):
  MdePkg: Refine casting expression result to bigger size

 MdePkg/Library/BaseLib/String.c                              |  4 ++--
 MdePkg/Library/BasePeCoffLib/BasePeCoff.c                    | 12 +++++-------
 MdePkg/Library/BaseS3PciLib/S3PciLib.c                       |  4 ++--
 MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c  |  4 ++--
 MdePkg/Library/UefiMemoryAllocationLib/MemoryAllocationLib.c |  4 ++--
 5 files changed, 13 insertions(+), 15 deletions(-)

-- 
1.9.5.msysgit.0



^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2017-01-25  6:19 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2017-01-24  7:25 [PATCH v2 0/1] Refine casting expression result to bigger size Hao Wu
2017-01-24  7:25 ` [PATCH v2 1/1] MdePkg: " Hao Wu
2017-01-24  9:53   ` Laszlo Ersek
2017-01-25  0:25     ` Wu, Hao A
2017-01-25  5:57       ` Gao, Liming
2017-01-25  6:16         ` Wu, Hao A
2017-01-25  6:19           ` Gao, Liming

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