• J. Liu and Y. Wu. Performance characterization of the 64-bit x86 architecture from compiler optimizations’ perspective.  In Proceedings of the International Conference on Compiler Construction, CC’06, 2006

http://www.springerlink.com/index/521324472703w117.pdf

• Test machines:
• Fedora 14/x86-64
• kernel-2.6.35.11-84.3.fc14
• glibc-2.13-1
• X32 glibc

• 181.mcf from SPEC CPU 2000 (memory bound):
• Intel Core i7
  
• ~32% faster than x86-64.
• ~1% slower than ia32.
• Sizes in bytes:

• Intel Atom
  
• ~28% faster than x86-64.
• ~0.5% slower than ia32.
• Sizes in bytes:

• X32 API is designed for environments where the current ia32 API is sufficient.  It can be viewed as ia32 with register extended to 64bit plus 8 more registers as well as IP relative address.  Everything else is still 32bit.
• X32 kernel interface uses the same kernel structure layouts as ia32, implemented with "syscall" instruction.
• Use the same 64bit system calls with 64bit arguments:
• Both 32bit and 64bit values can be passed in 64bit argument.
  
•  In kernel facing data structures, the long long field in struct/union is aligned at 4 byte, not 8 byte.
  
• The future x32 kernel system call interface:
• Should we change time_t from 32bit to 64bit?

• Install Fedora 15/x86-64 with the latest updates.
• Get x32 enabled rpms from
  

1. Update to x32 enabled yum first: # yum update yum
2. Update to x32 enabled rpm and kernel: # yum update
   
3. Install glibc x32 binary rpms: # yum install glibc-devel.x32glibc-static.x32
4. Untar x32 libgcc under /.
   

• Install the latest binutils:
• Download the latest binutils snapshot from:
  
  ftp://sourceware.org/pub/binutils/snapshots/binutils-2.21.51.tar.bz2
  

• Configure, build and install binutils as usual:
• ../configure --target=x86_64-pc-linux-gnu ....
• Make sure that the new x32 as, ld .... are in the front of your PATH such that they will be used by x32 GCC.

• Install x32 GDB:
• Check out hjl/x32 branch at:
  
  http://git.kernel.org/?p=devel/gdb/hjl/x86.git;a=summary
  
  
• Configure, build and install GDB as usual:
• ../configure --target=x86_64-pc-linux-gnu ....
  
• X32 GDB can debug ia32, x86-64 and x32 binaries.
  

• Install x32 GCC
  
• Check out GCC trunk.
• Configure GCC with --enable-languages=c,c++,fortran,objc --with-multilib-list=m32,m64,mx32
• Build and install x32 GCC:
• Copy x32 libgcc_s.so.1 to /libx32 by hand.
  
• X32 GCC supports:
• -m32: To generate ia32 binaries.
• -m64: To generate x86-64 binaries.
• -mx32: To generate x32 binaries.

• Build x32 glibc:
• Check out glibc hjl/x32 branch at:
  
  http://git.kernel.org/?p=devel/glibc/hjl/x86.git;a=summary
  

• Configure glibc with:

1. nptl/tst-cancel-wrappers.out
2. rt/tst-cpuclock2.out
3. rt/tst-cputimer1.out
   

• The target tuple is the same as an x86_64 system.  e.g. x86_64-linux
• The toolchain will support both x86_64 and x32 binaries.  The default is still x86_64, but x32 support can be selected by various flags at runtime:
• Selecting x32 depends on the tool:
• gas: --x32
• ld: -m elf32_x86_64
• gcc: -mx32
• gdb: bfd automatically detects things
• gcc will automatically pass the correct flags down to the assembler/linker when it is given -mx32 itself.
• Differences between x32 and x86_64:
• long and pointer sizes:
• X32: 32bits.
• X86_64: 64bits
• Library API is the same as ia32.
• To compile a package for x32:
• Always add -mx32 to compiler and configure it as x86-64:
• To configure C and C++ programs, use
• CC="gcc -mx32 " CXX="g++ -mx32" ./configure
  
• Add x32 support on existing x86_64 support:
• C/C++ codes:
• Use int64_t or long long instead of long for 64bit integer.
• Assembler codes:
• Use 32bit instructions on long and pointer.
• You can do

• GCC
• The current x32 implementation isn't optimized:
• Atom LEA optimization is disabled.
• Memory addressing should be optimized.
  
• Enable other languages for x32.