Hi,
Recently I upgraded my egcs compiler and noticed it can't compile
cvs postgres ( 6.4 probably too) on my linux x86 machine.
make[2]: Entering directory /home/postgres/cvs/pgsql/src/backend/postmaster'
gcc -I../../include -I../../backend -O2 -mpentium -Wall -Wmissing-prototypes -I.. -c postmaster.c -o postmaster.o
postmaster.c: In function `initMasks':
postmaster.c:802: Invalid `asm' statement:
postmaster.c:802: fixed or forbidden register 2 (cx) was spilled for class CREG.
make[2]: *** [postmaster.o] Error 1
make[2]: Leaving directory /home/postgres/cvs/pgsql/src/backend/postmaster'
make[1]: *** [postmaster.dir] Error 2
make[1]: Leaving directory /home/postgres/cvs/pgsql/src/backend'
make: *** [all] Error 2
gcc -v
Reading specs from /usr/local/egcs/lib/gcc-lib/i586-pc-linux-gnulibc1/egcs-2.92.21/specs
gcc version egcs-2.92.21 19981109 (gcc2 ss-980609 experimental)
Previous version of egcs does compile postgres ok.
I read egcs FAQ and found http://egcs.cygnus.com/faq.html/#asmclobber
........
Previous releases of gcc (for example, gcc-2.7.2.X) did not detect as invalid a clobber specifier that
clobbered an operand. Instead, it could spuriously and silently generate incorrect code for certain
non-obvious cases of source code. Even more unfortunately, the manual (Using and Porting GCC,
section Extended Asm, see the bug report entry) did not explicitly say that it was invalid to specify
clobber registers that were destined to overlap operands; it could arguably be interpreted that it was
correct to clobber an input operand to mark it as not holding a usable value after the asm.
For the general case, there is no way to tell whether a specified clobber is intended to overlap with a
specific (input) operand or is a program error, where the choice of actual register for operands failed to
avoid the clobbered register. Such unavoidable overlap is detected by versions egcs-2.92.18
19981104 and above, and flagged as an error rather than accepted. An error message is given, such
as:
foo.c: In function `foo':
foo.c:7: Invalid `asm' statement:
foo.c:7: fixed or forbidden register 0 (ax) was spilled for class AREG.
Unfortunately, a lot of existing software, for example the Linux kernel version 2.0.35 for the Intel x86,
has constructs where input operands are marked as clobbered.
.............
egcs becomes popular and people are going to use it and I think it
would be great if someone could fix the problem.
Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83