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.
Regstrapped on x86_64-linux-gnu and ppc64-linux-gnu. Ok to install?
for gcc/ChangeLog
* config/rs6000/rs6000.cc (TARGET_CALL_OFFSET_RETURN_LABEL):
Override.
(rs6000_call_offset_return_label): New.
---
gcc/config/rs6000/rs6000.cc | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 8e0b0d022db2f..e55117159b270 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -1760,6 +1760,9 @@ static const struct attribute_spec
rs6000_attribute_table[] =
#undef TARGET_UPDATE_IPA_FN_TARGET_INFO
#define TARGET_UPDATE_IPA_FN_TARGET_INFO rs6000_update_ipa_fn_target_info
+
+#undef TARGET_CALL_OFFSET_RETURN_LABEL
+#define TARGET_CALL_OFFSET_RETURN_LABEL rs6000_call_offset_return_label
/* Processor table. */
@@ -14593,6 +14596,22 @@ 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. */
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
