[binutils-gdb] s390: Fix displaced-stepping certain relative branch insns
Andreas Arnez
arnez@sourceware.org
Mon Mar 20 16:31:00 GMT 2017
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=dcb84eda0c5f25835251a311c4d6704e70cfa498
commit dcb84eda0c5f25835251a311c4d6704e70cfa498
Author: Andreas Arnez <arnez@linux.vnet.ibm.com>
Date: Mon Mar 20 17:30:01 2017 +0100
s390: Fix displaced-stepping certain relative branch insns
On s390x targets GDB can not handle displaced stepping correctly for some
relative branch instructions, such as cij (compare immediate and branch
relative). When setting a breakpoint on such an instruction and
single-stepping over it, the branch is never taken. This is because the
check in s390_displaced_step_fixup for relative branch instructions is
incomplete.
Instead of completing the list of relative branch instructions to check
against, this patch just treats relative branches and non-branching
instructions in the same way and adjusts the PC with the negated
displacement in both cases.
gdb/ChangeLog:
* s390-linux-tdep.c (is_rsi, is_rie): Remove functions.
(s390_displaced_step_fixup): Cover relative branches with the
default fixup handling. This fixes lack of support for some
relative branch instructions.
Diff:
---
gdb/ChangeLog | 7 +++++++
gdb/s390-linux-tdep.c | 55 ++++-----------------------------------------------
2 files changed, 11 insertions(+), 51 deletions(-)
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9061347..2cff118 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2017-03-20 Andreas Arnez <arnez@linux.vnet.ibm.com>
+
+ * s390-linux-tdep.c (is_rsi, is_rie): Remove functions.
+ (s390_displaced_step_fixup): Cover relative branches with the
+ default fixup handling. This fixes lack of support for some
+ relative branch instructions.
+
2017-03-17 Simon Marchi <simon.marchi@polymtl.ca>
* i386-gnu-nat.c (gnu_fetch_registers, gnu_store_registers): Use
diff --git a/gdb/s390-linux-tdep.c b/gdb/s390-linux-tdep.c
index abc9438..2af2c7a 100644
--- a/gdb/s390-linux-tdep.c
+++ b/gdb/s390-linux-tdep.c
@@ -1212,41 +1212,6 @@ is_rsy (bfd_byte *insn, int op1, int op2,
static int
-is_rsi (bfd_byte *insn, int op,
- unsigned int *r1, unsigned int *r3, int *i2)
-{
- if (insn[0] == op)
- {
- *r1 = (insn[1] >> 4) & 0xf;
- *r3 = insn[1] & 0xf;
- /* i2 is a 16-bit signed quantity. */
- *i2 = (((insn[2] << 8) | insn[3]) ^ 0x8000) - 0x8000;
- return 1;
- }
- else
- return 0;
-}
-
-
-static int
-is_rie (bfd_byte *insn, int op1, int op2,
- unsigned int *r1, unsigned int *r3, int *i2)
-{
- if (insn[0] == op1
- && insn[5] == op2)
- {
- *r1 = (insn[1] >> 4) & 0xf;
- *r3 = insn[1] & 0xf;
- /* i2 is a 16-bit signed quantity. */
- *i2 = (((insn[2] << 8) | insn[3]) ^ 0x8000) - 0x8000;
- return 1;
- }
- else
- return 0;
-}
-
-
-static int
is_rx (bfd_byte *insn, int op,
unsigned int *r1, int *d2, unsigned int *x2, unsigned int *b2)
{
@@ -1976,20 +1941,6 @@ s390_displaced_step_fixup (struct gdbarch *gdbarch,
amode | (from + insnlen));
}
- /* Handle PC-relative branch instructions. */
- else if (is_ri (insn, op1_brc, op2_brc, &r1, &i2)
- || is_ril (insn, op1_brcl, op2_brcl, &r1, &i2)
- || is_ri (insn, op1_brct, op2_brct, &r1, &i2)
- || is_ri (insn, op1_brctg, op2_brctg, &r1, &i2)
- || is_rsi (insn, op_brxh, &r1, &r3, &i2)
- || is_rie (insn, op1_brxhg, op2_brxhg, &r1, &r3, &i2)
- || is_rsi (insn, op_brxle, &r1, &r3, &i2)
- || is_rie (insn, op1_brxlg, op2_brxlg, &r1, &r3, &i2))
- {
- /* Update PC. */
- regcache_write_pc (regs, pc - to + from);
- }
-
/* Handle LOAD ADDRESS RELATIVE LONG. */
else if (is_ril (insn, op1_larl, op2_larl, &r1, &i2))
{
@@ -2004,9 +1955,11 @@ s390_displaced_step_fixup (struct gdbarch *gdbarch,
else if (insn[0] == 0x0 && insn[1] == 0x1)
regcache_write_pc (regs, from);
- /* For any other insn, PC points right after the original instruction. */
+ /* For any other insn, adjust PC by negated displacement. PC then
+ points right after the original instruction, except for PC-relative
+ branches, where it points to the adjusted branch target. */
else
- regcache_write_pc (regs, from + insnlen);
+ regcache_write_pc (regs, pc - to + from);
if (debug_displaced)
fprintf_unfiltered (gdb_stdlog,
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