Re: [PATCH 1/5] MdePkg/BasePrintLib: avoid absolute addresses for error strings

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

On 6/10/20 10:17 AM, Ard Biesheuvel wrote:
> The mStatusString[] is constructed as an array of pointer-to-char, which
> means that on X64 or AARCH64, it is emitted as a single linear list of
> 64-bit quantities, each containing the absolute address of one of the
> string literals in memory.
> 
> This means that each string takes up 8 bytes of additional space, along
> with 2 bytes of relocation data. It also means that the array cannot be
> used until PE/COFF relocation has completed, and so the following
> invocation
> 
>      Status = PeCoffLoaderRelocateImage (&ImageContext);
>      ASSERT_EFI_ERROR (Status);
> 
> that we will be introducing into StandaloneMmCore entrypoint for AARCH64
> to relocate the executable on the fly is guaranteed to return bogus output
> or crash, which is less than helpful.
> 
> So fix both issues, by emitting mStatusString as an array of char arrays
> instead. The memory footprint increases from 955 to 975 bytes, but given
> that in the latter case, the overhead consists of 410 NUL characters
> rather than 390 bytes worth of absolute addresses and relocation records,
> the impact on a compressed image is actually positive. For example, when
> building ArmVirtQemu.dsc in RELEASE mode for AARCH64 with the GCC5 profile,
> I get:
> 
>    Before
> 
>    FV Space Information
>    FVMAIN [99%Full] 4784768 total, 4784720 used, 48 free
>    FVMAIN_COMPACT [38%Full] 2093056 total, 811560 used, 1281496 free
> 
>    After
> 
>    FV Space Information
>    FVMAIN [99%Full] 4780672 total, 4780624 used, 48 free
>    FVMAIN_COMPACT [38%Full] 2093056 total, 813488 used, 1279568 free
> 
> So the compressed image is 4 KB smaller, whereas the entire image is
> < 2 KB larger, which is in the order of 0.2 %
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

Actually, I found a slightly better way of doing this, by applying the 
following delta on top, i.e., split the errors and warnings, and use an 
array of 21 byte character arrays for the former.

My build went from

FV Space Information

FVMAIN [99%Full] 4784768 total, 4784720 used, 48 free
FVMAIN_COMPACT [37%Full] 2093056 total, 792984 used, 1300072 free

to

FV Space Information
FVMAIN [99%Full] 4780672 total, 4780624 used, 48 free
FVMAIN_COMPACT [37%Full] 2093056 total, 791072 used, 1301984 free


in this case, i.e., both compressed and non-compressed images are 
slightly smaller.



--- a/MdePkg/Library/BasePrintLib/PrintLibInternal.c
+++ b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
@@ -27,13 +27,16 @@

  GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 mHexStr[] = 
{'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};

-GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 mStatusString[][25] = {
+GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 mWarningString[][25] = {
    "Success",                      //  RETURN_SUCCESS                = 0
    "Warning Unknown Glyph",        //  RETURN_WARN_UNKNOWN_GLYPH     = 1
    "Warning Delete Failure",       //  RETURN_WARN_DELETE_FAILURE    = 2
    "Warning Write Failure",        //  RETURN_WARN_WRITE_FAILURE     = 3
    "Warning Buffer Too Small",     //  RETURN_WARN_BUFFER_TOO_SMALL  = 4
    "Warning Stale Data",           //  RETURN_WARN_STALE_DATA        = 5
+};
+
+GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 mErrorString[][21] = {
    "Load Error",                   //  RETURN_LOAD_ERROR             = 
1  | MAX_BIT
    "Invalid Parameter",            //  RETURN_INVALID_PARAMETER      = 
2  | MAX_BIT
    "Unsupported",                  //  RETURN_UNSUPPORTED            = 
3  | MAX_BIT
@@ -996,12 +999,12 @@ BasePrintLibSPrintMarker (
            //
            Index = Status & ~MAX_BIT;
            if (Index > 0 && Index <= ERROR_STATUS_NUMBER) {
-            ArgumentString = mStatusString [Index + WARNING_STATUS_NUMBER];
+            ArgumentString = mErrorString [Index - 1];
            }
          } else {
            Index = Status;
            if (Index <= WARNING_STATUS_NUMBER) {
-            ArgumentString = mStatusString [Index];
+            ArgumentString = mWarningString [Index];
            }
          }
          if (ArgumentString == ValueBuffer) {


> ---
>   MdePkg/Library/BasePrintLib/PrintLibInternal.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/MdePkg/Library/BasePrintLib/PrintLibInternal.c b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
> index b6ec5ac4fbb9..c8b932c7e07a 100644
> --- a/MdePkg/Library/BasePrintLib/PrintLibInternal.c
> +++ b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
> @@ -27,7 +27,7 @@
>   
>   GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 mHexStr[] = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
>   
> -GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 * CONST mStatusString[] = {
> +GLOBAL_REMOVE_IF_UNREFERENCED CONST CHAR8 mStatusString[][25] = {
>     "Success",                      //  RETURN_SUCCESS                = 0
>     "Warning Unknown Glyph",        //  RETURN_WARN_UNKNOWN_GLYPH     = 1
>     "Warning Delete Failure",       //  RETURN_WARN_DELETE_FAILURE    = 2
>