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Subject: [Bug breakpoints/27009] [s390] GDB branches randomly for BC
 instruction while displaced stepping
Date: Sun, 06 Dec 2020 10:31:15 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27009

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gn=
u.org> ---
The gdb-10-branch branch has been updated by Joel Brobecker
<brobecke@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=3Dbinutils-gdb.git;h=3D47c4623c7587=
a0008597a4a10a7f32bbac1f7ad4

commit 47c4623c7587a0008597a4a10a7f32bbac1f7ad4
Author: Giancarlo Frix <gfrix@rocketsoftware.com>
Date:   Sun Dec 6 14:30:53 2020 +0400

    s390: Fix BC instruction breakpoint handling

    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.

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