docs/internals/multiple-architectures.txt

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Guide to multiple architecture support
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Valgrind supports systems where binaries for more than one architecture
can be run and will allow all sorts of binaries to be run under valgrind.

To support this the valgrind build system can now build multiple versions
of the coregrind library and the VEX library and then build and link multiple
versions of each tool.

The configure script selects which architectures to build support for
by defining a conditional for each platform that indicates whether or
not support for that platform should be built. There are currently three
such conditionals:

  VG_X86_LINUX
  VG_AMD64_LINUX
  VG_PPC32_LINUX

On an amd64 system both VG_X86_LINUX and VG_AMD64_LINUX will be true
so that two versions of all the tools will be built. The coregrind
libraries will be named:

  libcoregrind_x86_linux.a
  libcoregrind_amd64_linux.a

and the VEX libraries:

  libvex_x86_linux.a
  libvex_amd64_linux.a

Each tool will then be built twice, along with any preload library
for the tool and the core preload libraries. At install time one
subdirectory will be created in the valgrind library directory for
each supported platforms and the tools and shared objects will be
installed in the appropriate place. On amd64 the result will be:

  <prefix>/lib/valgrind
  <prefix>/lib/valgrind/default.supp
  <prefix>/lib/valgrind/glibc-2.4.supp
  <prefix>/lib/valgrind/hp2ps
  <prefix>/lib/valgrind/amd64-linux
  <prefix>/lib/valgrind/amd64-linux/vgpreload_core.so
  <prefix>/lib/valgrind/amd64-linux/vgpreload_massif.so
  <prefix>/lib/valgrind/amd64-linux/cachegrind
  <prefix>/lib/valgrind/amd64-linux/memcheck
  <prefix>/lib/valgrind/amd64-linux/helgrind
  <prefix>/lib/valgrind/amd64-linux/massif
  <prefix>/lib/valgrind/amd64-linux/vgpreload_memcheck.so
  <prefix>/lib/valgrind/amd64-linux/lackey
  <prefix>/lib/valgrind/amd64-linux/none
  <prefix>/lib/valgrind/amd64-linux/vgpreload_helgrind.so
  <prefix>/lib/valgrind/xfree-3.supp
  <prefix>/lib/valgrind/x86-linux
  <prefix>/lib/valgrind/x86-linux/vgpreload_core.so
  <prefix>/lib/valgrind/x86-linux/vgpreload_massif.so
  <prefix>/lib/valgrind/x86-linux/cachegrind
  <prefix>/lib/valgrind/x86-linux/memcheck
  <prefix>/lib/valgrind/x86-linux/helgrind
  <prefix>/lib/valgrind/x86-linux/massif
  <prefix>/lib/valgrind/x86-linux/vgpreload_memcheck.so
  <prefix>/lib/valgrind/x86-linux/lackey
  <prefix>/lib/valgrind/x86-linux/none
  <prefix>/lib/valgrind/x86-linux/vgpreload_helgrind.so
  <prefix>/lib/valgrind/glibc-2.3.supp
  <prefix>/lib/valgrind/xfree-4.supp
  <prefix>/lib/valgrind/glibc-2.2.supp

The launcher program (ie the valgrind binary itself) is always
built as a native program (so a 64 bit program on amd64) but will
peek at the program which it is being asked to run and decide which
of the possible tools to run taking both the requested tool and the
format of the program being run into account.

Because the execv system call is now routed back through the launcher
it is also possible to exec an x86 program from an amd64 program and
vice versa.