Re: [PATCH 1/1] UefiCpuPkg/PiSmmCpuDxeSmm: fix format string

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

On 3/24/23 15:56, Laszlo Ersek wrote:
> Hi Gerd,
> 
> On 3/24/23 14:41, Gerd Hoffmann wrote:
>> BufferPages is UINTN, so we need "%Lu" when printing it.
>>
>> Fixes: 4f441d024bee ("UefiCpuPkg/PiSmmCpuDxeSmm: fix error handling")
>> Reported-by: Laszlo Ersek <lersek@redhat.com>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>> ---
>>  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
>> index cf69161caa4b..08663b1b1ab4 100644
>> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
>> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.c
>> @@ -880,7 +880,7 @@ PiCpuSmmEntry (
>>      BufferPages = EFI_SIZE_TO_PAGES (SIZE_32KB + TileSize * (mMaxNumberOfCpus - 1));
>>      Buffer      = AllocateAlignedCodePages (BufferPages, SIZE_4KB);
>>      if (Buffer == NULL) {
>> -      DEBUG ((DEBUG_ERROR, "Failed to allocate %d pages.\n", BufferPages));
>> +      DEBUG ((DEBUG_ERROR, "Failed to allocate %Lu pages.\n", BufferPages));
>>        CpuDeadLoop ();
>>        return EFI_OUT_OF_RESOURCES;
>>      }
> 
> you missed part of my off-list comment; it was:
> 
>> "BufferPages" has type UINTN, it should not be printed with "%d" (%d
>> is for INT32). The proper way to print a UINTN value with DEBUG is to
>> cast the value to UINT64, and print that with %Lu (or %Lx).
> 
> Refer to "cast the value to UINT64".
> 
> UINTN is either UINT32 or UINT64. There is no format specifier that's
> dedicated specifically to UINTN. You can't use fixed %u with UINTN
> because that will be wrong on 64-bit platforms (%u takes UINT32 but
> UINTN will be UINT64), and you can't use fixed %Lu with UINTN because
> that will be wrong on 32-bit platforms (%Lu takes UINT64 but UINTN will
> be UINT32). The proper way is to (1) cast the UINTN to UINT64 first
> (which will be a no-op on 64-bit platforms, and it will widen UINT32 to
> UINT64 on 32-bit platforms, without changing the value), and then (2)
> print *that* (the now certainly UINT64 value) with %Lu.
> 
>   DEBUG ((
>     DEBUG_ERROR,
>     "Failed to allocate %Lu pages.\n",
>     (UINT64)BufferPages
>     ));
> 
> (
> 
> Here's an idea:
> 
>> diff --git a/MdePkg/Include/Library/PrintLib.h b/MdePkg/Include/Library/PrintLib.h
>> index 8d523cac528d..bdacec9777f0 100644
>> --- a/MdePkg/Include/Library/PrintLib.h
>> +++ b/MdePkg/Include/Library/PrintLib.h
>> @@ -197,6 +197,17 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
>>  #define PREFIX_ZERO   0x20
>>  #define RADIX_HEX     0x80
>>
>> +#if defined (MDE_CPU_AARCH64) || defined (MDE_CPU_LOONGARCH64) || \
>> +    defined (MDE_CPU_RISCV64) || defined (MDE_CPU_X64)
>> +#define PRIuN "%Lu"
>> +#define PRIxN "%Lx"
>> +#elif defined (MDE_CPU_ARM) || defined (MDE_CPU_IA32)
>> +#define PRIuN "%Lu"
>> +#define PRIxN "%Lx"

aargh, how annoying. I'm in a rush, sorry. I over-edited this code and
forgot to remove the "L" from the latter two.

Laszlo

>> +#else
>> +#error Unknown CPU architecture.
>> +#endif
>> +
>>  /**
>>    Produces a Null-terminated Unicode string in an output buffer based on
>>    a Null-terminated Unicode format string and a VA_LIST argument list.
> 
> and then you could do
> 
>   DEBUG ((
>     DEBUG_ERROR,
>     "Failed to allocate " PRIuN " pages.\n",
>     BufferPages
>     ));
> 
> (Note the lack of a cast.)
> 
> Note: I do not cover MDE_CPU_EBC above, in "PrintLib.h". I don't know
> how EBC (EFI Byte Code) deals with 32-bit vs. 64-bit. The UEFI 2.10 spec
> says in "22.1.1 Processor Architecture Independence": "64-bit C source
> code" and "The interpreter handles 32 vs. 64 bit issues". Unfortunately,
> that doesn't seem to help: it does not help us decide the size of UINTN
> at compile time.
> 
> More precisely: if you check "MdePkg/Include/Ebc/ProcessorBind.h", it
> contains:
> 
>> ///
>> /// Signed value of native width.  (4 bytes on supported 32-bit processor instructions,
>> /// 8 bytes on supported 64-bit processor instructions)
>> /// "long" type scales to the processor native size with EBC compiler
>> ///
>> typedef long INTN;
>> ///
>> /// The unsigned value of native width.  (4 bytes on supported 32-bit processor instructions;
>> /// 8 bytes on supported 64-bit processor instructions)
>> /// "long" type scales to the processor native size with the EBC compiler.
>> ///
>> typedef unsigned long UINTN;
> 
> In other words, the size of UINTN *is* chosen at compile time, but the
> choice cannot be determined from MDE_CPU_EBC. And no other macro that
> "MdePkg/Include/Ebc/ProcessorBind.h" defines seems to be suitable for
> investigation with #if preprocessing directives.
> 
> Anyway: the explicit (UINT64) cast with the open-coded %Lu conversion
> specifier will work fine on EBC as well, so I suggest sticking with
> that.
> 
> )
> 
> Laszlo