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S390: Fix displaced stepping of "basr r,0"

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The BASR instruction behaves differently depending on whether the second
operand is a number from 1 to 15, or zero.  In the former case BASR jumps
to the address contained in the general register of that number, but in
the latter case no jump is performed.  GDB's displaced-stepping logic does
not distinguish these cases, although it should.

This is fixed.  In the case where no jump is performed the PC is adjusted
to point back after the original instruction.  Otherwise the PC is left
alone.

gdb/ChangeLog:

	* s390-tdep.c (s390_displaced_step_fixup): Adjust PC for a
	non-branching basr.
This commit is contained in:
Andreas Arnez 2018-07-13 12:46:14 +02:00
parent a780ef4f27
commit 5c1eda30f5
2 changed files with 8 additions and 0 deletions
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5
gdb/ChangeLog
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@ -1,3 +1,8 @@
2018-07-13 Andreas Arnez <arnez@linux.vnet.ibm.com>
* s390-tdep.c (s390_displaced_step_fixup): Adjust PC for a
non-branching basr.
2018-07-12 Philippe Waroquiers <philippe.waroquiers@skynet.be>
* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add

3
gdb/s390-tdep.c
View File

@ -492,6 +492,9 @@ s390_displaced_step_fixup (struct gdbarch *gdbarch,
/* Recompute saved return address in R1. */
regcache_cooked_write_unsigned (regs, S390_R0_REGNUM + r1,
amode | (from + insnlen));
/* Update PC iff the instruction doesn't actually branch. */
if (insn[0] == op_basr && r2 == 0)
regcache_write_pc (regs, from + insnlen);
}
/* Handle absolute branch instructions. */