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[gdb] Add gdbarch_dwarf2_reg_piece_offset hook

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In rw_pieced_value, when reading/writing part of a register, DW_OP_piece and
DW_OP_bit_piece are handled the same, but the standard tells us:
- DW_OP_piece: if the piece is located in a register, but does not occupy the
  entire register, the placement of the piece within that register is defined
  by the ABI.
- DW_OP_bit_piece: if the location is a register, the offset is from the least
  significant bit end of the register.

Add a new hook gdbarch_dwarf2_reg_piece_offset that allows us to define the
ABI-specific behaviour for DW_OP_piece.

The default implementation of the hook is the behaviour of DW_OP_bit_piece, so
there should not be any functional changes.

Tested on s390x-linux.

Approved-By: Tom Tromey <tom@tromey.com>
This commit is contained in:
Tom de Vries
2025-01-15 17:02:00 +01:00
parent c4606bdbd5
commit b034bb3877
6 changed files with 91 additions and 6 deletions
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31
gdb/dwarf2/expr.c
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@@ -211,14 +211,33 @@ rw_pieced_value (value *v, value *from, bool check_optimized)
ULONGEST reg_bits = 8 * register_size (arch, gdb_regnum);
int optim, unavail;
if (gdbarch_byte_order (arch) == BFD_ENDIAN_BIG
&& p->offset + p->size < reg_bits)
if (p->offset + p->size < reg_bits)
{
/* Big-endian, and we want less than full size. */
bits_to_skip += reg_bits - (p->offset + p->size);
/* We want less than full size. */
if (p->op == DW_OP_piece)
{
gdb_assert (p->offset == 0);
/* If the piece is located in a register, but does not
occupy the entire register, the placement of the piece
within that register is defined by the ABI. */
bits_to_skip
+= 8 * gdbarch_dwarf2_reg_piece_offset (arch, gdb_regnum,
p->size / 8);
}
else if (p->op == DW_OP_bit_piece)
{
/* If the location is a register, the offset is from the
least significant bit end of the register. */
if (gdbarch_byte_order (arch) == BFD_ENDIAN_BIG)
bits_to_skip += reg_bits - (p->offset + p->size);
else
bits_to_skip += p->offset;
}
else
error (_("Don't know how to get part of implicit pointer"));
}
else
bits_to_skip += p->offset;
this_size = bits_to_bytes (bits_to_skip, this_size_bits);
buffer.resize (this_size);