Package: gcc-3.3 Version: 1:3.3.2-0pre4 Severity: normal Tags: patch DEC Unix provides both IEEE conformant and IEEE nonconformant libraries, and links against the appropriate libraries based on the setting of eflag 48 (set implicitly by specifying -mieee or explicitly by specifying -mieee-conformant).
Linux neither supports linking based on eflag 48, nor does it provide IEEE nonconformant libraries (the GNU math libraries are conformant, and the maintainers/developers seem to have no intent of ever releasing a special nonconformant version for the Alpha). As a result, under Linux (and any other GNU based system), programs must be IEEE conformant (compiled with -mieee) in order to work with the system libraries in all circumstances. This fact is frequently overlooked (or not known) by most package maintainers, and has result in numerous packages that SIGFPE for no apparent reason. Well many of these packages can be 'fixed' (and several have been) by adding a lines to the effect of ifeq ($(DEB_TARGET_ARCH),alpha) CFLAGS += -mieee CXXFLAGS += -mieee endif to the appropriate package's debian/rules file, this is not really a satisfactory solution. It creates a situation where users of the Debian Alpha distribution are continuously having to file yet another Alpha SIGFPE bug against some new package. In reality, the real problem is that GCC's defaults, not generating IEEE conformant code, do not match Linux's defaults, IEEE conformant libraries. The easiest way to rectify this situation is to change GCC's default behavior. Attached is a dpatch file that does this, updates the documentation, and adds a switch (-mno-ieee) to make it possible to still generate IEEE nonconformant code for those who desire to do so. In addition to adding it to the debian/patches directory, the Alpha specific section of debian/rules.patch has to be modified to include it ifeq ($(DEB_TARGET_ARCH),alpha) debian_patches += alpha-ieee endif The very very few apps whos performance this impacts negatively (possibly the FFTW libraries, not LAPACK of BLAS though, they require IEEE conformance) can have full performance restored by updating the Alpha specific portion of their debian/rules file to include the -mno-ieee flag. This represents significantly less work (by several orders of magnitude) then the current practice of continually having to add the -mieee flag all the other packages. :) NOTES ON PERFORMANCE IMPACT: Obviously this will not 'break' existing applications. Less obvious is that it does not impose a serious performance penalty on pre-EV6 architectures for the vast majority of applications. Testing on an Alpha EV56 CPU reveals that intensive tightly looped math operations [FFT transforms] run at most 20% slower, while intensive numerical simulations [Molecular Dynamics, MC Option pricing] run between 1% to 5% slower. The effect on other applications (i.e. 99.99% of packages) is not measurable. SOME BROKEN COMMON APPLICATIONS CURRENTLY NOT COMPILED WITH -mieee: python: type 1e-320 at the prompt kspread: type =erfc(27) in a cell mpg321: play a mp3 file back through the ARTS backend konqueror: goto http://news.independent.co.uk A quick scan of the /usr/lib on a local Beowulf cluster reveals just how wide spread the requirement for -mieee is. Of the 589 installed libraries in /usr/lib that use the FPU, only 98 have have not been compiled with -mieee. Of all the numerics relates libraries installed (LAPACK, BLAS, etc), the only one compiled without -mieee is the GNU multi-precision library -- System Information: Debian Release: testing/unstable Architecture: alpha Kernel: Linux whitehead 2.4.21 #26 Wed Jun 25 12:35:13 EDT 2003 alpha Locale: LANG=C, LC_CTYPE=C Versions of packages gcc-3.3 depends on: ii binutils 2.14.90.0.6-2 The GNU assembler, linker and bina ii cpp-3.3 1:3.3.2-0pre4 The GNU C preprocessor ii gcc-3.3-base 1:3.3.2-0pre4 The GNU Compiler Collection (base ii libc6.1 2.3.2-8 GNU C Library: Shared libraries an ii libgcc1 1:3.3.2-0pre4 GCC support library -- no debconf information
/usr/src/alpha-ieee.dpatch
Description: application/shellscript
