[PATCH] gdbserver: i387_cache_to_xsave: fix copy dest of zmm registers

[Simon Marchi]

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
---
 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 4229d60327e6..27f8e2dbb73f 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.  */

base-commit: 7fdd4fcee1c6698daa8eb5f52017e768b0771503
-- 
2.42.0