Probe Overview

From ATLAS 3.7.12 on, ATLAS's config routine was rewritten for greater modularity, with each config probe having its own driver and so on. For this discussion, we will refer to the machine doing the cross-compiliation as the frontend (abbreviated as FE), and the machine which ATLAS is being tuned for the backend (abbreviated as BE). Note that if you are not doing cross-compilation (the majority of the time) the front-end and back-end are the same machine.

Every type of probe has a frontend driver (occasionally, config may directly call the backend driver, if there is only one) which will itself call multiple backend drivers. For instance, the probe to compute the architecure runs on the frontend, and calls different backend drivers depending on the assembly dialect and operating system of the backend. The files for the frontend drivers are located in ATLAS/CONFIG/src, and the backend files are in ATLAS/CONFIG/src/backend, with all include files in ATLAS/CONFIG/include. All frontend probes use the file atlconf_misc.c (prototyped in atlconf_misc.h), which handles things like file I/O, issuing shell commands, etc. The current probes used by config are:

1. OS Probe

   Purpose:

   Discover the Operating System being used

   Inputs:

   None

   Outputs:

   Enumerated type of OS

   FE files:

   probe_OS.c

   BE files:

   None (uname on BE)

2. Assembly dialect probe

   Purpose:

   Discover what ATLAS assembly dialect works

   Inputs:

   OS enum (gives subdialect of assembler)

   Outputs:

   Enum of assembly dialect

   FE files:

   probe_asm.c,

   BE files:

   probe_this_asm.c - [probe_gas_parisc.S, probe_gas_ppc.S, probe_gas_sparc.S, probe_gas_x8632.S, probe_gas_x8664.S]

3. Vector ISA extension probe - assembly

   Purpose:

   Discover which of supported vector ISA extensions work

   Inputs:

   enums for OS and assembly dialect

   Outputs:

   iflag = ( (1<<ISA0) | (1<<ISA1) | ... | (1<<ISAn) )

   FE files:

   probe_vec.c

   BE files:

   probe_svec.c - [probe_AltiVec.S, probe_SSE.S], probe_dvec.c - [probe_SSE2.S], probe_dSSE3.c -[probe_SSE3.S]

4. Vector ISA extension probe - C: Write this later, using C-inline statements for platforms where we don't speak the assembly, but can still use peter's vector include file
5. Architecture probe

   Purpose:

   Discover target architecure/machine

   Inputs:

   OS and assembly enums [force 64/32 bit usage]

   Outputs:

   enum of arch

   FE files:

   archinfo.c

   BE files:

   archinfo_x86.c, archinfo_linux.c, archinfo_freebsd.c, archinfo_aix.c, archinfo_irix.c, archinfo_sunos.c

   Notes:

   See Section 10.2 for more details.

6. 64-bit probe

   Purpose:

   Discover if arch supports 64-bit pointers

   Inputs:

   OS, arch [user choice]

   Outputs:

   32 / 64

   files:

   Config directly calls archinfo

   Notes:

   : New policy: config assumes whatever compiler gives you w/o -m32 -m64, and user must throw special flag to append these to the line.

7. Compiler probe

   Purpose:

   Find good compilers

   Inputs:

   OS, arch [,suggested compilers]

   Outputs:

   The following:

   1. F2CNAME, F2CINT, F2CSTRING enums
   2. Compilers and flags

   FE files

   : probe_comp.c probe_f2c.c probe_ccomp.c

   BE files

   : f2cname[F,C].[f,c], f2cint[F,C].[f,c], f2cstr[F,C].[f,c], ccomp interaction not yet done

   Note:

   This is complex, see Section 10.4 for details.

8. Arch defaults probe

   Purpose:

   Discover arch defaults

   Inputs:

   OS, arch, compilers

   Outputs:

   Whether to use arch defs (INSTFLAGS in Make.inc

   files:

   ARCHS/Makefile

   invoke:

   Arch default setup is instigated by atlas_install.c.

   notes:

   May want to have it autobenchmark kernel, test against table of expected perf, to see if arch def are OK wt this compiler version.