>>> 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. Or wait, no, your description of the issue is wrong: It actually is the folding of the two REX prefixes which causes the problem, since that results in the replacement instruction being one byte longer than the to be replaced one. > 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. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
