Sorry, this is the wrong patch. I will post it again.
On Fri, Dec 08, 2023 at 05:57:12PM +0800, Yang Yujie wrote:
> 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
