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s390: Fix BC instruction breakpoint handling

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This fixes a long-lived bug in the s390 port.

When trying to step over a breakpoint set on a BC (branch on condition)
instruction with displaced stepping on IBM Z, gdb would incorrectly
adjust the pc regardless of whether or not the branch was taken. Since
the branch target is an absolute address, this would cause the inferior
to jump around wildly whenever the branch was taken, either crashing it
or causing it to behave unpredictably.

It turns out that the logic to handle BC instructions correctly was in
the code, but that the enum value representing its opcode has always
been incorrect.

This patch corrects the enum value to the actual opcode, fixing the
stepping problem. The enum value is also used in the prologue analysis
code, so this also fixes a minor bug where more of the prologue would
be read than was necessary.

gdb/ChangeLog:

        PR breakpoints/27009
        * s390-tdep.h (op_bc): Correct BC opcode value.
This commit is contained in:
Giancarlo Frix 2020-12-06 14:27:52 +04:00 committed by Joel Brobecker
parent 63c457b911
commit 296cfb8889
2 changed files with 6 additions and 1 deletions
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5
gdb/ChangeLog
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@ -1,3 +1,8 @@
2020-12-06 Giancarlo Frix <gfrix@rocketsoftware.com> (tiny change)
PR breakpoints/27009
* s390-tdep.h (op_bc): Correct BC opcode value.
2020-12-06 Joel Brobecker <brobecker@adacore.com>
* gmp-utils.h (gdb_mpz::safe_export): New private method.

2
gdb/s390-tdep.h
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@ -117,7 +117,7 @@ enum
op_basr = 0x0d,
op_bas = 0x4d,
op_bcr = 0x07,
op_bc = 0x0d,
op_bc = 0x47,
op_bctr = 0x06,
op_bctgr = 0xb946,
op_bct = 0x46,