https://gcc.gnu.org/g:0bb10f149bfcbe874d348814c623b36e9232cb3f
commit 0bb10f149bfcbe874d348814c623b36e9232cb3f
Author: Alexandre Oliva <ol...@adacore.com>
Date: Wed May 29 02:52:10 2024 -0300
[rs6000] adjust return_pc debug attrs
Some of the rs6000 call patterns, on some ABIs, issue multiple opcodes
out of a single call insn, but the call (bl) or jump (b) is not always
the last opcode in the sequence.
This does not seem to be a problem for exception handling tables, but
the return_pc attribute in the call graph output in dwarf2+ debug
information, that takes the address of a label output right after the
call, does not match the value of the link register even for non-tail
calls. E.g., with ABI_AIX or ABI_ELFv2, such code as:
foo ();
outputs:
bl foo
nop
LVL#:
[...]
.8byte .LVL# # DW_AT_call_return_pc
but debug info consumers may rely on the return_pc address, and draw
incorrect conclusions from its off-by-4 value.
This patch uses the infrastructure for targets to add an offset to the
label issued after the call_insn to set the call_return_pc attribute,
on rs6000, to account for opcodes issued after actual call opcode as
part of call insns output patterns.
for gcc/ChangeLog
* config/rs6000/rs6000.cc (TARGET_CALL_OFFSET_RETURN_LABEL):
Override.
(rs6000_call_offset_return_label): New.
Diff:
---
gcc/config/rs6000/rs6000.cc | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index e4dc629ddcc..77e6b94a539 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -1779,6 +1779,8 @@ static const scoped_attribute_specs *const
rs6000_attribute_table[] =
#undef TARGET_OVERLAP_OP_BY_PIECES_P
#define TARGET_OVERLAP_OP_BY_PIECES_P hook_bool_void_true
+#undef TARGET_CALL_OFFSET_RETURN_LABEL
+#define TARGET_CALL_OFFSET_RETURN_LABEL rs6000_call_offset_return_label
/* Processor table. */
@@ -14822,6 +14824,22 @@ rs6000_assemble_integer (rtx x, unsigned int size, int
aligned_p)
return default_assemble_integer (x, size, aligned_p);
}
+/* Return the offset to be added to the label output after CALL_INSN
+ to compute the address to be placed in DW_AT_call_return_pc. */
+
+static int
+rs6000_call_offset_return_label (rtx_insn *call_insn)
+{
+ /* All rs6000 CALL_INSN output patterns start with a b or bl, always
+ a 4-byte instruction, but some output patterns issue other
+ opcodes afterwards. The return label is issued after the entire
+ call insn, including any such post-call opcodes. Instead of
+ figuring out which cases need adjustments, we compute the offset
+ back to the address of the call opcode proper, then add the
+ constant 4 bytes, to get the address after that opcode. */
+ return 4 - get_attr_length (call_insn);
+}
+
/* Return a template string for assembly to emit when making an
external call. FUNOP is the call mem argument operand number. */
