Hi all,
I'm having a weird problem at a client's. They need a toolchain for both
Windows (cygwin) and Linux. What's more, then need the two toolchains to
match exactly - given identical source code, the toolchains must produce
the exact same machine code (tested by doing objdump -d and diffing the
outputs). The toolchains are for bare metal power-pc (powerpc-eabi target).
At first I just compiled gcc and newlib on both systems, but the results
from compilation varied greatly. I traced it down to cygwin and Debian
Lenny providing different versions of the supporting libraries (mpfr
etc), which caused to optimizer to perform different different
optimizations, producing correct, but different, results when compiling
the same code on Windows or on Linux.
For my second run, I compiled all supporting libraries as well. I made
sure to run "make check" on every step. I got two toolchains, and
compiled newlib and the actual project with both. This time, the results
were noticeably better. The newlib libraries, as well as some of the
libraries for the project, did compile the same with the Linux and the
Cygwin toolchains. Some libraries, however, did not. Again, this does
not appear to be a case of the compiler producing wrong code, just
different.
In case you are wondering, I made sure that the code the compiler sees
is identical between the build environments, by stopping after the
pre-processor stage and comparing the files. Except for the source file
paths, the files post-pre-processing and pre-compilation are identical.
One thing that was different between the setups was the native compiler
version used to compile the cross compiler itself. With Cygwin, I used
gcc 4.3.4 to compile the libraries and gcc, on Linux I used gcc 4.4.3.
In both cases, the cross compiler itself is gcc 4.4.3 with fairly latest
versions of everything. While I am definitely going to next try
compiling on Linux with 4.3.4, I fail to see how the version of the
compiler has such an effect on the output of the program.
Since this question is some what recursive, I'll try to recap in the
form of a table:
Cygwin 1.7
Linux Debian Lenny/Sid
Use native gcc-4.3.4 to build toolchain
Use native gcc-4.4.3 (from Sid) to build toolchain
Build native mpc-0.8.1, mpfr-2.4.2, gmp-4.3.2, cloog-ppl-0.15.7,
ppl-0.10.2 using gcc-4.3.4 as static objects
Build the same libraries as on the left using gcc-4.4.3, with same
configure options, except as shared objects
Build cross binutils-2.20.51 and gcc-4.4.3 using gcc-4.3.4
Build the same versions of binutils and gcc using gcc-4.4.3. Same
command line options
Build newlib-1.18.0 using the cross-gcc 4.4.3 compiled in the previous step
Build the same version using the gcc compiled in the previous step.
Same configure options
Build the client's project using the above toolchain
Build the client's project using the above toolchain
The newlib libraries built are compared, and are identical down to the
last assembly instruction. The client libraries are compared. Some are
identical, some are not.
Any thoughts and/or suggestions are welcome.
Shachar
--
Shachar Shemesh
Lingnu Open Source Consulting Ltd.
http://www.lingnu.com
_______________________________________________
Linux-il mailing list
Linux-il@cs.huji.ac.il
http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
