• Michael Holzheu's avatar
    [S390] Fix stfle() lowcore protection problem · 37e37c20
    Michael Holzheu authored
    
    
    The stfle() function writes into lowcore memory when stfl_fac_list
    is initialized with "S390_lowcore.stfl_fac_list = 0". For older
    compilers this triggers a lowcore exception. With newer compilers
    and "-OXX" compile option the bug does not show up because
    the "S390_lowcore.stfl_fac_list" initialization is removed by the
    compiler. The reason for thatis the incorrect "=m"
    (S390_lowcore.stfl_fac_list) constraint in the stfl inline assembly.
    
    The following shows the disassembly of the stfle() optimized code
    that is inlined in the lgr_info_get() function:
    
    000000000011325c <lgr_info_get>:
      11325c:       eb 9f f0 60 00 24       stmg    %r9,%r15,96(%r15)
      113262:       c0 d0 00 29 0e 47       larl    %r13,634ef0 <servi..>
      113268:       a7 f1 3f c0             tml     %r15,16320
      11326c:       b9 04 00 ef             lgr     %r14,%r15
      113270:       a7 84 00 01             je      113272 <lgr_info_g..>
      113274:       a7 fb ff c0             aghi    %r15,-64
      113278:       b9 04 00 c2             lgr     %r12,%r2
      11327c:       a7 29 00 01             lghi    %r2,1
      113280:       e3 e0 f0 98 00 24       stg     %r14,152(%r15)
      113286:       d7 97 c0 00 c0 00       xc      0(152,%r12),0(%r12)
      11328c:       c0 e5 00 28 db 4c       brasl   %r14,62e924 <add_e..>
      113292:       b2 b1 00 00             stfl    0
    
    To fix the problem we now clear the S390_lowcore.stfl_fac_list at
    startup in "head.S" for all machine types before lowcore protection
    is enabled.
    
    In addition to that the "=m" constraint is replaced by "+m".
    Signed-off-by: default avatarMichael Holzheu <holzheu@linux.vnet.ibm.com>
    Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
    37e37c20
head.S 14.8 KB