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+From: Xavier Leroy <xavier.leroy@college-de-france.fr>
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+Date: Thu, 29 Aug 2024 12:08:16 +0200
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+Subject: Don't use r12 to pass size to caml_call_realloc_stack
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+
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+The temporary r12 can be destroyed by a PLT shim.
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+Instead, use r27 (a non-temporary register, not used at OCaml function entry).
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+
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+Origin: https://github.com/ocaml/ocaml/pull/13410
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+---
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+ asmcomp/power/emit.mlp | 3 ++-
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+ runtime/power.S | 6 +++---
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+ 2 files changed, 5 insertions(+), 4 deletions(-)
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+
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+diff --git a/asmcomp/power/emit.mlp b/asmcomp/power/emit.mlp
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+index 47f5419..70a6a0f 100644
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+--- a/asmcomp/power/emit.mlp
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++++ b/asmcomp/power/emit.mlp
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+@@ -996,8 +996,9 @@ let fundecl fundecl =
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+ || max_frame_size >= stack_threshold_size then begin
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+ let overflow = new_label () and ret = new_label () in
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+ (* The return address is saved in a register not used for param passing *)
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++ (* The size is passed in a register normally not used for param passing *)
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+ `{emit_label overflow}: mflr 28\n`;
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+- ` li 12, {emit_int (Config.stack_threshold + max_frame_size / 8)}\n`;
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++ ` li 27, {emit_int (Config.stack_threshold + max_frame_size / 8)}\n`;
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+ emit_call "caml_call_realloc_stack";
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+ emit_call_nop ();
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+ ` mtlr 28\n`;
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+diff --git a/runtime/power.S b/runtime/power.S
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+index bfb37fa..9e5b243 100644
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+--- a/runtime/power.S
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++++ b/runtime/power.S
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+@@ -358,16 +358,16 @@
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+ caml_system__code_begin:
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+
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+ /* Reallocate the stack when it is too small. */
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+-/* Desired size is passed in register TMP2. */
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++/* Desired size is passed in register r27. */
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+
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+ FUNCTION caml_call_realloc_stack
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+ /* Save return address in caller's frame. */
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+ mflr 0
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+ std 0, LR_SAVE(SP)
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+ /* Save all registers, as well as ALLOC_PTR and TRAP_PTR */
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+- SAVE_ALL_REGS /* TMP2 is preserved */
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++ SAVE_ALL_REGS /* r27 is preserved */
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+ /* Recover desired size, to be passed in r3 */
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+- mr 3, TMP2
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++ mr 3, 27
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+ /* Switch stacks and call caml_try_realloc_stack */
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+ SWITCH_OCAML_TO_C
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52
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+ Far_call(caml_try_realloc_stack) |