[binutils-gdb] gdbserver: i387_cache_to_xsave: fix copy dest of zmm registers

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=41770089162edd23ea7ae33b7952585316accde5

commit 41770089162edd23ea7ae33b7952585316accde5
Author: Simon Marchi <simon.marchi@efficios.com>
Date:   Fri Sep 1 14:12:07 2023 -0400

    gdbserver: i387_cache_to_xsave: fix copy dest of zmm registers
    
    On a machine with AVX512 support (AMD EPYC 9634), I see these failures:
    
        $ make check TESTS="gdb.arch/i386-avx512.exp" RUNTESTFLAGS="--target_board=native-gdbserver"
        ...
        FAIL: gdb.arch/i386-avx512.exp: check contents of zmm_data[16] after writing ZMM regs
        FAIL: gdb.arch/i386-avx512.exp: check contents of zmm_data[17] after writing ZMM regs
        FAIL: gdb.arch/i386-avx512.exp: check contents of zmm_data[18] after writing ZMM regs
        ...
    
    The problem can be reduced to:
    
        (gdb) print $zmm16.v8_int64
        $1 = {0, 0, 0, 0, 0, 0, 0, 0}
        (gdb) print $zmm16.v8_int64 = {11,22,33,44,55,66,77,88}
        $2 = {11, 22, 33, 44, 55, 66, 77, 88}
        (gdb) print $zmm16.v8_int64
        $3 = {11, 22, 33, 44, 55, 66, 77, 88}
        (gdb) step
        5               ++x;
        (gdb) print $zmm16.v8_int64
        $4 = {11, 22, 77, 88, 0, 0, 0, 0}
    
    Writing to the local regcache in GDB works fine, but the writeback to
    gdbserver (which happens when resuming / stepping) doesn't work (the
    code being stepped doesn't touch AVX registers, so we don't expect the
    value of zmm16 to change when stepping).
    
    The problem is on the gdbserver side, the zmmh and ymmh portions of the
    zmm register are not memcpied at the right place in the xsave buffer.  Fix
    that.  Note now how the two modified memcpy calls match the memcmp calls
    just above them.
    
    With this patch, gdb.arch/i386-avx512.exp passes completely for me.
    
    Change-Id: I22c417e0f5e88d4bc635a0f08f8817a031c76433
    Reviewed-by: John Baldwin <jhb@FreeBSD.org>
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30818

Diff:
---
 gdbserver/i387-fp.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdbserver/i387-fp.cc b/gdbserver/i387-fp.cc
index 4229d60327e..27f8e2dbb73 100644
--- a/gdbserver/i387-fp.cc
+++ b/gdbserver/i387-fp.cc
@@ -469,7 +469,7 @@ i387_cache_to_xsave (struct regcache *regcache, void *buf)
 	  if (memcmp (raw, p + 32, 32) != 0)
 	    {
 	      xstate_bv |= X86_XSTATE_ZMM;
-	      memcpy (p, raw, 32);
+	      memcpy (p + 32, raw, 32);
 	    }
 
 	  /* YMMH sub-register.  */
@@ -477,7 +477,7 @@ i387_cache_to_xsave (struct regcache *regcache, void *buf)
 	  if (memcmp (raw, p + 16, 16) != 0)
 	    {
 	      xstate_bv |= X86_XSTATE_ZMM;
-	      memcpy (p, raw, 16);
+	      memcpy (p + 16, raw, 16);
 	    }
 
 	  /* XMM sub-register.  */