S390: Recognize special jumps in prologue parser
Commit Message
Functions compiled with the gcc option `-mhotpatch' may start with a
branch-never BRCL instruction as a 6-byte NOP. And functions compiled
with `-mstack-size' contain a BRC instruction in their prologue that is
actually a conditional trap. Both of these special jumps cause the
prologue parser to stop and yield bad unwinding results.
This change makes the prologue analyzer recognize such special jumps and
ignore them.
gdb/ChangeLog:
* s390-linux-tdep.c (s390_analyze_prologue): Ignore BRC and BRCL
instructions that do nothing or are conditional traps.
---
gdb/s390-linux-tdep.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
Comments
Pushed.
On Mon, Mar 07 2016, Andreas Arnez wrote:
> Functions compiled with the gcc option `-mhotpatch' may start with a
> branch-never BRCL instruction as a 6-byte NOP. And functions compiled
> with `-mstack-size' contain a BRC instruction in their prologue that is
> actually a conditional trap. Both of these special jumps cause the
> prologue parser to stop and yield bad unwinding results.
>
> This change makes the prologue analyzer recognize such special jumps and
> ignore them.
>
> gdb/ChangeLog:
>
> * s390-linux-tdep.c (s390_analyze_prologue): Ignore BRC and BRCL
> instructions that do nothing or are conditional traps.
@@ -1567,13 +1567,25 @@ s390_analyze_prologue (struct gdbarch *gdbarch,
break;
}
+ /* BRC/BRCL -- branch relative on condition. Ignore "branch
+ never", branch to following instruction, and "conditional
+ trap" (BRC +2). Otherwise terminate search. */
+ else if (is_ri (insn, op1_brc, op2_brc, &r1, &i2))
+ {
+ if (r1 != 0 && i2 != 1 && i2 != 2)
+ break;
+ }
+ else if (is_ril (insn, op1_brcl, op2_brcl, &r1, &i2))
+ {
+ if (r1 != 0 && i2 != 3)
+ break;
+ }
+
/* Terminate search when hitting any other branch instruction. */
else if (is_rr (insn, op_basr, &r1, &r2)
|| is_rx (insn, op_bas, &r1, &d2, &x2, &b2)
|| is_rr (insn, op_bcr, &r1, &r2)
|| is_rx (insn, op_bc, &r1, &d2, &x2, &b2)
- || is_ri (insn, op1_brc, op2_brc, &r1, &i2)
- || is_ril (insn, op1_brcl, op2_brcl, &r1, &i2)
|| is_ril (insn, op1_brasl, op2_brasl, &r2, &i2))
break;