On 12/02/16 08:23, Jan Beulich wrote: >>>> On 11.02.16 at 20:25, <andrew.coop...@citrix.com> wrote: >> CentOS 7 gets into trouble when compiling Xen citing: >> >> flushtlb.c: Assembler messages: >> flushtlb.c:149: Error: value of 256 too large for field of 1 bytes at 1 >> >> The line number is wrong, and the error message not helpful. It turns out >> that the intermediate generated assembly was >> >> # 139 "arch/x86/flushtlb.c" 1 >> 661: >> rex clflush (%r15) >> 662: >> .pushsection .altinstructions,"a" >> >> and it was having trouble combining the explicit REX prefix with the REX.B >> required for the use of %r15. > What gas version is this? I just checked with 2.20, which has no > problem combining an explicit with a generated REX prefix.
bash-4.2$ as --version GNU assembler version 2.23.52.0.1-30.el7_1.2 20130226 > Or > wait, no, your description of the issue is wrong: It actually is the > folding of the two REX prefixes which causes the problem, This is what I said. What do you think I meant with "trouble combining the" ? > since > that results in the replacement instruction being one byte longer > than the to be replaced one. But that is still the case with an explicit %ds override. The assembler still has to insert an extra byte somehow. > >> Follow what Linux does and use a redundant %ds prefix instead, for a final >> generated instruction of `3e 41 0f ae 3f` >> >> While modifying this line, fix the indentation which was out by one space. >> >> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> > I think before committing I'll extend your patch by introducing > and using Linux'es NOP_DS_PREFIX. Ok. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
