Updates:
v1 -> v2: Add a test case.
v2 -> v3: Fix code format.
v3 -> v4: Fix code format. Avoid unwanted optimization in the test.
On Fri, Dec 08, 2023 at 05:54:46PM +0800, Yang Yujie wrote:
> On LoongArch, the regitsters $r4 - $r7 (EH_RETURN_DATA_REGNO) will be saved
> and restored in the function prologue and epilogue if the given function calls
> __builtin_eh_return. This causes the return value to be overwritten on normal
> return paths and breaks a rare case of libgcc's _Unwind_RaiseException.
>
> gcc/ChangeLog:
>
> * config/loongarch/loongarch.cc: Do not restore the saved eh_return
> data registers ($r4-$r7) for a normal return of a function that calls
> __builtin_eh_return elsewhere.
> * config/loongarch/loongarch-protos.h: Same.
> * config/loongarch/loongarch.md: Same.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/loongarch/eh_return-normal-return.c: New test.
> ---
> gcc/config/loongarch/loongarch-protos.h | 2 +-
> gcc/config/loongarch/loongarch.cc | 41 ++++++++++++-------
> gcc/config/loongarch/loongarch.md | 18 +++++++-
> .../loongarch/eh_return-normal-return.c | 32 +++++++++++++++
> 4 files changed, 76 insertions(+), 17 deletions(-)
> create mode 100644
> gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
>
> diff --git a/gcc/config/loongarch/loongarch-protos.h
> b/gcc/config/loongarch/loongarch-protos.h
> index cb8fc36b086..af20b5d7132 100644
> --- a/gcc/config/loongarch/loongarch-protos.h
> +++ b/gcc/config/loongarch/loongarch-protos.h
> @@ -60,7 +60,7 @@ enum loongarch_symbol_type {
> extern rtx loongarch_emit_move (rtx, rtx);
> extern HOST_WIDE_INT loongarch_initial_elimination_offset (int, int);
> extern void loongarch_expand_prologue (void);
> -extern void loongarch_expand_epilogue (bool);
> +extern void loongarch_expand_epilogue (int);
> extern bool loongarch_can_use_return_insn (void);
>
> extern bool loongarch_symbolic_constant_p (rtx, enum loongarch_symbol_type
> *);
> diff --git a/gcc/config/loongarch/loongarch.cc
> b/gcc/config/loongarch/loongarch.cc
> index 3545e66a10e..9c0e0dd1b73 100644
> --- a/gcc/config/loongarch/loongarch.cc
> +++ b/gcc/config/loongarch/loongarch.cc
> @@ -1015,20 +1015,30 @@ loongarch_save_restore_reg (machine_mode mode, int
> regno, HOST_WIDE_INT offset,
>
> static void
> loongarch_for_each_saved_reg (HOST_WIDE_INT sp_offset,
> - loongarch_save_restore_fn fn)
> + loongarch_save_restore_fn fn,
> + bool skip_eh_data_regs_p)
> {
> HOST_WIDE_INT offset;
>
> /* Save the link register and s-registers. */
> offset = cfun->machine->frame.gp_sp_offset - sp_offset;
> for (int regno = GP_REG_FIRST; regno <= GP_REG_LAST; regno++)
> - if (BITSET_P (cfun->machine->frame.mask, regno - GP_REG_FIRST))
> - {
> - if (!cfun->machine->reg_is_wrapped_separately[regno])
> - loongarch_save_restore_reg (word_mode, regno, offset, fn);
> + {
> + /* Special care needs to be taken for $r4-$r7 (EH_RETURN_DATA_REGNO)
> + when returning normally from a function that calls __builtin_eh_return.
> + In this case, these registers are saved but should not be restored,
> + or the return value may be clobbered. */
>
> - offset -= UNITS_PER_WORD;
> - }
> + if (BITSET_P (cfun->machine->frame.mask, regno - GP_REG_FIRST))
> + {
> + if (!(cfun->machine->reg_is_wrapped_separately[regno]
> + || (skip_eh_data_regs_p
> + && GP_ARG_FIRST <= regno && regno < GP_ARG_FIRST + 4)))
> + loongarch_save_restore_reg (word_mode, regno, offset, fn);
> +
> + offset -= UNITS_PER_WORD;
> + }
> + }
>
> /* This loop must iterate over the same space as its companion in
> loongarch_compute_frame_info. */
> @@ -1297,7 +1307,7 @@ loongarch_expand_prologue (void)
> GEN_INT (-step1));
> RTX_FRAME_RELATED_P (emit_insn (insn)) = 1;
> size -= step1;
> - loongarch_for_each_saved_reg (size, loongarch_save_reg);
> + loongarch_for_each_saved_reg (size, loongarch_save_reg, false);
> }
>
> /* Set up the frame pointer, if we're using one. */
> @@ -1382,11 +1392,11 @@ loongarch_can_use_return_insn (void)
> return reload_completed && cfun->machine->frame.total_size == 0;
> }
>
> -/* Expand an "epilogue" or "sibcall_epilogue" pattern; SIBCALL_P
> - says which. */
> +/* Expand function epilogue for the following insn patterns:
> + "epilogue" (style == 0) / "sibcall_epilogue" (1) / "eh_return" (2). */
>
> void
> -loongarch_expand_epilogue (bool sibcall_p)
> +loongarch_expand_epilogue (int style)
> {
> /* Split the frame into two. STEP1 is the amount of stack we should
> deallocate before restoring the registers. STEP2 is the amount we
> @@ -1403,7 +1413,8 @@ loongarch_expand_epilogue (bool sibcall_p)
> bool need_barrier_p
> = (get_frame_size () + cfun->machine->frame.arg_pointer_offset) != 0;
>
> - if (!sibcall_p && loongarch_can_use_return_insn ())
> + /* Handle simple returns. */
> + if (style == 0 && loongarch_can_use_return_insn ())
> {
> emit_jump_insn (gen_return ());
> return;
> @@ -1479,7 +1490,8 @@ loongarch_expand_epilogue (bool sibcall_p)
>
> /* Restore the registers. */
> loongarch_for_each_saved_reg (frame->total_size - step2,
> - loongarch_restore_reg);
> + loongarch_restore_reg,
> + crtl->calls_eh_return && style != 2);
>
> if (need_barrier_p)
> loongarch_emit_stack_tie ();
> @@ -1504,7 +1516,8 @@ loongarch_expand_epilogue (bool sibcall_p)
> emit_insn (gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx,
> EH_RETURN_STACKADJ_RTX));
>
> - if (!sibcall_p)
> + /* Emit return unless doing sibcall. */
> + if (style != 1)
> emit_jump_insn (gen_simple_return_internal (ra));
> }
>
> diff --git a/gcc/config/loongarch/loongarch.md
> b/gcc/config/loongarch/loongarch.md
> index 7a101dd64b7..61b27293489 100644
> --- a/gcc/config/loongarch/loongarch.md
> +++ b/gcc/config/loongarch/loongarch.md
> @@ -3197,7 +3197,7 @@ (define_expand "epilogue"
> [(const_int 2)]
> ""
> {
> - loongarch_expand_epilogue (false);
> + loongarch_expand_epilogue (0);
> DONE;
> })
>
> @@ -3205,7 +3205,7 @@ (define_expand "sibcall_epilogue"
> [(const_int 2)]
> ""
> {
> - loongarch_expand_epilogue (true);
> + loongarch_expand_epilogue (1);
> DONE;
> })
>
> @@ -3262,6 +3262,20 @@ (define_expand "eh_return"
> emit_insn (gen_eh_set_ra_di (operands[0]));
> else
> emit_insn (gen_eh_set_ra_si (operands[0]));
> +
> + emit_jump_insn (gen_eh_return_internal ());
> + emit_barrier ();
> + DONE;
> +})
> +
> +(define_insn_and_split "eh_return_internal"
> + [(eh_return)]
> + ""
> + "#"
> + "epilogue_completed"
> + [(const_int 0)]
> +{
> + loongarch_expand_epilogue (2);
> DONE;
> })
>
> diff --git a/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
> b/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
> new file mode 100644
> index 00000000000..da7e98a35bd
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
> @@ -0,0 +1,32 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +
> +#include <stdlib.h>
> +
> +int foo () __attribute__((noinline));
> +int main ();
> +
> +int
> +foo () {
> +
> + int t;
> +
> + /* prevent optimization using asm */
> + asm ("" : "=r" (t) : "0" (-1));
> + asm ("" : "=r" (t) : "0" (t ? 1 : 0));
> +
> + if (t == 0)
> + /* never reached */
> + __builtin_eh_return (0, __builtin_return_address (0));
> + else
> + return 202312;
> +}
> +
> +int
> +main ()
> +{
> + if (foo() == 202312)
> + return 0;
> + else
> + abort ();
> +}
> --
> 2.43.0
