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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: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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