Use the cpuid instruction to generate the CPU brand string. And

base/cpu.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/cpu.h"
 
 #include <string.h>
 
 #include "build/build_config.h"
 
@@ skipping 66 matching lines @@
   );
 }
 
 #endif
 #endif  // _MSC_VER
 #endif  // ARCH_CPU_X86_FAMILY
 
 void CPU::Initialize() {
 #if defined(ARCH_CPU_X86_FAMILY)
   int cpu_info[4] = {-1};
-  char cpu_string[0x20];
-
+  char cpu_string[32];

[Mark Mentovai, 2012/10/03 18:34:02]

Now let’s make this stuff conform to Chromium style a little better. Don’t
declare variables until they’re used.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Local_...

+  char cpu_brand[48];

[Mark Mentovai, 2012/10/03 18:34:02]

You can share a buffer for cpu_string and cpu_brand as long as it’s sized
appropriately, since the two buffers aren’t both needed at the same time.

If you share the buffer, you obviously won’t be able to use sizeof(BUF) where I
recommend you do that below, but the alternatives should be very obvious.

+  const int para_end = 0x80000004;

[Mark Mentovai, 2012/10/03 18:34:02]

Don’t abbreviate.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Genera...

   // __cpuid with an InfoType argument of 0 returns the number of
   // valid Ids in CPUInfo[0] and the CPU identification string in
   // the other three array elements. The CPU identification string is
   // not in linear order. The code below arranges the information
   // in a human readable form.
   //
   // More info can be found here:
   // http://msdn.microsoft.com/en-us/library/hskdteyh.aspx

[Mark Mentovai, 2012/10/03 18:34:02]

This URL is no longer valid. You should remove it, unless you can find a current
URL, in which case you can revise it.

   __cpuid(cpu_info, 0);
   int num_ids = cpu_info[0];
   memset(cpu_string, 0, sizeof(cpu_string));
   *(reinterpret_cast<int*>(cpu_string)) = cpu_info[1];

[Mark Mentovai, 2012/10/03 18:34:02]

Fix these existing broken assignments to use memcpy as well, although
unfortunately the string is stored non-contiguously in cpu_info, so you will
need EITHER three memcpys (meh) OR you’ll need to std::swap ecx with edx
(cpu_info[3] with cpu_info[2]) and do a single memcpy. You can get rid of the
memset.

Put spaces around the + operators when you make this change.

   *(reinterpret_cast<int*>(cpu_string+4)) = cpu_info[3];
   *(reinterpret_cast<int*>(cpu_string+8)) = cpu_info[2];

[Mark Mentovai, 2012/10/03 18:34:02]

cpu_string is char[32] but it only needs to be char[12]. However, when you do
that, you lose the NUL terminator. To address that, you should change line 114
from |cpu_vendor_ = cpu_string;| to |cpu_vendor_.assign(cpu_string,
sizeof(cpu_string));|.

 
   // Interpret CPU feature information.
   if (num_ids > 0) {
     __cpuid(cpu_info, 1);
     stepping_ = cpu_info[0] & 0xf;
     model_ = ((cpu_info[0] >> 4) & 0xf) + ((cpu_info[0] >> 12) & 0xf0);
     family_ = (cpu_info[0] >> 8) & 0xf;
     type_ = (cpu_info[0] >> 12) & 0x3;
     ext_model_ = (cpu_info[0] >> 16) & 0xf;
     ext_family_ = (cpu_info[0] >> 20) & 0xff;
     cpu_vendor_ = cpu_string;

[Mark Mentovai, 2012/10/03 18:34:02]

This doesn’t seem to require num_ids to be > 0. You can move this out of the
|num_ids > 0| conditional. You should set cpu_vendor_ as soon as you’ve gotten
cpu_string worked out.

     has_mmx_ = (cpu_info[3] & 0x00800000) != 0;
     has_sse_ = (cpu_info[3] & 0x02000000) != 0;
     has_sse2_ = (cpu_info[3] & 0x04000000) != 0;
     has_sse3_ = (cpu_info[2] & 0x00000001) != 0;
     has_ssse3_ = (cpu_info[2] & 0x00000200) != 0;
     has_sse41_ = (cpu_info[2] & 0x00080000) != 0;
     has_sse42_ = (cpu_info[2] & 0x00100000) != 0;
+
+    // get the brand string of the cpu.

[Mark Mentovai, 2012/10/03 18:34:02]

Comments should be written as sentences, and sentences start with capital
letters.
http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Punctu...

[Mark Mentovai, 2012/10/03 18:34:02]

I don’t think there’s any reason for this to be in the |num_ids > 0|
conditional. The “basic” and “extended” groups of cpuid are totally distinct.

+    __cpuid(cpu_info, 0x80000000);
+
+    if (cpu_info[0] >= para_end) {
+      memset(cpu_brand, 0, sizeof(cpu_brand));

[Mark Mentovai, 2012/10/03 18:34:02]

You don’t need this memset, because you’re going to memcpy over cpu_brand
anyway.

+      char* cpu_brand_ptr = cpu_brand;
+
+      for (int parameter = 0x80000002; parameter <= para_end; parameter++) {
+        __cpuid(cpu_info, parameter);
+        memcpy(cpu_brand_ptr, cpu_info, sizeof(cpu_info));
+        cpu_brand_ptr += sizeof(cpu_info);
+      }
+      cpu_brand_ = cpu_brand;

[Mark Mentovai, 2012/10/03 18:34:02]

cpu_brand is not necessarily NUL-terminated as you’ve written things here
(although cpuid is SUPPOSED to return a NUL-terminated string, I wouldn’t rely
on that). See the comment above about NUL-termination for cpu_string, and
address this in the same way that you deal with that.

[jar (doing other things), 2012/10/04 17:42:03]

I couldn't find documentation that suggests the string comes null terminated. 
The sample documentation provides sample code that does the null termination,
and worse yet, the example given shows the CPU_vendor_ string to be:

GenuineIntel

which is 12 characters long... plus an unsupplied null termination byte.  Hence
that string is not supplied null terminated earlier, and probably this string is
not terminated here either.

[Mark Mentovai, 2012/10/04 18:00:45]

jar wrote:
The string in ebx-edx-ecx from cpuid 0 is not NUL-terminated, either in practice
or in documentation. As you say, it’s 12 characters long and the three 32-bit
registers only have room for 12 characters, so there’s no way for it to be
NUL-terminated.

The “brand string” returned by cpuid 0x80000002-0x80000004 is documented as
being NUL-terminated. Ref. Intel64 and IA-32 Architecture Software Developer’s
Manual, vol. 2A (Intel 253666,
http://download.intel.com/products/processor/manual/253666.pdf), August 2012,
vol. 2A page 3-168, CPUID/Methods for Returning Branding Information/How Brand
Stings Work. Ref. also AMD CPUID Specification (AMD 25481,
http://support.amd.com/us/Embedded_TechDocs/25481.pdf), September 2010, page 22,
2 CPUID Function Specification/CPUID Fn8000_000[4:2]_E[D,C,B,A]X Processor Name
String Identifier.

I still wouldn’t rely on that because we’re putting our buffer overflow (or not)
into the control of some external data or our ability to properly call cpuid and
memcpy in this loop. I’d always be precise with the lengths, which is what the
latest patch set does.

+    }
   }
 #endif
 }
 
 }  // namespace base