ping
> [Differences from V1:
> - Prototype for call_from_call_insn moved before comment block.
> - Reuse the `call' flag for SYMBOL_REF_LIBCALL.
> - Fallback to check REG_CALL_DECL in non-direct calls.
> - New test to check correct behavior for non-direct calls.]
>
> There are many places in GCC where alternative local sequences are
> tried in order to determine what is the cheapest or best alternative
> to use in the current target. When any of these sequences involve a
> libcall, the current implementation of emit_library_call_value_1
> introduce a side-effect consisting on emitting an external declaration
> for the funcall (such as __divdi3) which is thus emitted even if the
> sequence that does the libcall is not retained.
>
> This is problematic in targets such as BPF, because the kernel loader
> chokes on the spurious symbol __divdi3 and makes the resulting BPF
> object unloadable. Note that BPF objects are not linked before being
> loaded.
>
> This patch changes emit_library_call_value_1 to mark the target
> SYMBOL_REF as a libcall. Then, the emission of the external
> declaration is done in the first loop of final.cc:shorten_branches.
> This happens only if the corresponding sequence has been kept.
>
> Regtested in x86_64-linux-gnu.
> Tested with host x86_64-linux-gnu with target bpf-unknown-none.
>
> gcc/ChangeLog
>
> * rtl.h (SYMBOL_REF_LIBCALL): Define.
> * calls.cc (emit_library_call_value_1): Do not emit external
> libcall declaration here.
> * final.cc (shorten_branches): Do it here.
>
> gcc/testsuite/ChangeLog
>
> * gcc.target/bpf/divmod-libcall-1.c: New test.
> * gcc.target/bpf/divmod-libcall-2.c: Likewise.
> * gcc.c-torture/compile/libcall-2.c: Likewise.
> ---
> gcc/calls.cc | 9 +++---
> gcc/final.cc | 30 +++++++++++++++++++
> gcc/rtl.h | 5 ++++
> .../gcc.c-torture/compile/libcall-2.c | 8 +++++
> .../gcc.target/bpf/divmod-libcall-1.c | 19 ++++++++++++
> .../gcc.target/bpf/divmod-libcall-2.c | 16 ++++++++++
> 6 files changed, 83 insertions(+), 4 deletions(-)
> create mode 100644 gcc/testsuite/gcc.c-torture/compile/libcall-2.c
> create mode 100644 gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
> create mode 100644 gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
>
> diff --git a/gcc/calls.cc b/gcc/calls.cc
> index 1f3a6d5c450..219ea599b16 100644
> --- a/gcc/calls.cc
> +++ b/gcc/calls.cc
> @@ -4388,9 +4388,10 @@ emit_library_call_value_1 (int retval, rtx orgfun, rtx
> value,
> || argvec[i].partial != 0)
> update_stack_alignment_for_call (&argvec[i].locate);
>
> - /* If this machine requires an external definition for library
> - functions, write one out. */
> - assemble_external_libcall (fun);
> + /* Mark the emitted target as a libcall. This will be used by final
> + in order to emit an external symbol declaration if the libcall is
> + ever used. */
> + SYMBOL_REF_LIBCALL (fun) = 1;
>
> original_args_size = args_size;
> args_size.constant = (aligned_upper_bound (args_size.constant
> @@ -4735,7 +4736,7 @@ emit_library_call_value_1 (int retval, rtx orgfun, rtx
> value,
> valreg,
> old_inhibit_defer_pop + 1, call_fusage, flags, args_so_far);
>
> - if (flag_ipa_ra)
> + if (flag_ipa_ra || SYMBOL_REF_LIBCALL (orgfun))
> {
> rtx datum = orgfun;
> gcc_assert (GET_CODE (datum) == SYMBOL_REF);
> diff --git a/gcc/final.cc b/gcc/final.cc
> index dd3e22547ac..2041e43fdd1 100644
> --- a/gcc/final.cc
> +++ b/gcc/final.cc
> @@ -804,6 +804,8 @@ make_pass_compute_alignments (gcc::context *ctxt)
> }
>
>
> +static rtx call_from_call_insn (rtx_call_insn *insn);
> +
> /* Make a pass over all insns and compute their actual lengths by shortening
> any branches of variable length if possible. */
>
> @@ -850,6 +852,34 @@ shorten_branches (rtx_insn *first)
> for (insn = get_insns (), i = 1; insn; insn = NEXT_INSN (insn))
> {
> INSN_SHUID (insn) = i++;
> +
> + /* If this is a `call' instruction implementing a libcall, and
> + this machine requires an external definition for library
> + functions, write one out. */
> + if (CALL_P (insn))
> + {
> + rtx x;
> +
> + if ((x = call_from_call_insn (dyn_cast <rtx_call_insn *> (insn)))
> + && (x = XEXP (x, 0))
> + && MEM_P (x)
> + && (x = XEXP (x, 0))
> + && SYMBOL_REF_P (x)
> + && SYMBOL_REF_LIBCALL (x))
> + {
> + /* Direct call. */
> + assemble_external_libcall (x);
> + }
> + else if ((x = find_reg_note (insn, REG_CALL_DECL, NULL_RTX))
> + && (x = XEXP (x, 0)))
> + {
> + /* Indirect call with REG_CALL_DECL note. */
> + gcc_assert (SYMBOL_REF_P (x));
> + if (SYMBOL_REF_LIBCALL (x))
> + assemble_external_libcall (x);
> + }
> + }
> +
> if (INSN_P (insn))
> continue;
>
> diff --git a/gcc/rtl.h b/gcc/rtl.h
> index e1c51156f90..28be708a55f 100644
> --- a/gcc/rtl.h
> +++ b/gcc/rtl.h
> @@ -334,6 +334,7 @@ struct GTY((desc("0"), tag("0"),
> 1 in a CALL_INSN logically equivalent to
> ECF_LOOPING_CONST_OR_PURE and DECL_LOOPING_CONST_OR_PURE_P.
> 1 in a VALUE is SP_DERIVED_VALUE_P in cselib.cc.
> + 1 in a SYMBOL_REF if it is the target of a libcall.
> Dumped as "/c" in RTL dumps. */
> unsigned int call : 1;
> /* 1 in a REG, MEM, or CONCAT if the value is set at most once, anywhere.
> @@ -2734,6 +2735,10 @@ do {
> \
> #define SYMBOL_REF_USED(RTX) \
> (RTL_FLAG_CHECK1 ("SYMBOL_REF_USED", (RTX), SYMBOL_REF)->used)
>
> +/* 1 if RTX is a symbol_ref that represents a libcall target. */
> +#define SYMBOL_REF_LIBCALL(RTX) \
> + (RTL_FLAG_CHECK1 ("SYMBOL_REF_LIBCALL", (RTX), SYMBOL_REF)->call)
> +
> /* 1 if RTX is a symbol_ref for a weak symbol. */
> #define SYMBOL_REF_WEAK(RTX) \
> (RTL_FLAG_CHECK1 ("SYMBOL_REF_WEAK", (RTX), SYMBOL_REF)->return_val)
> diff --git a/gcc/testsuite/gcc.c-torture/compile/libcall-2.c
> b/gcc/testsuite/gcc.c-torture/compile/libcall-2.c
> new file mode 100644
> index 00000000000..b33944c83ff
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/libcall-2.c
> @@ -0,0 +1,8 @@
> +/* Make sure that external refences for libcalls are generated even for
> + indirect calls. */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mcmodel=large" { target x86_64-*-* } } */
> +/* { dg-final { scan-assembler "globl\t__divti3" } } */
> +
> +__int128 a, b; void foo () { a = a / b; }
> diff --git a/gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
> b/gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
> new file mode 100644
> index 00000000000..7481076602a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
> @@ -0,0 +1,19 @@
> +/* This test makes sure that no spurious external symbol declarations are
> + emitted for libcalls in tried but eventually not used code sequences. */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mcpu=v3" } */
> +/* { dg-final { scan-assembler-not "global\t__divdi3" } } */
> +/* { dg-final { scan-assembler-not "global\t__moddi3" } } */
> +
> +int
> +foo (unsigned int len)
> +{
> + return ((unsigned long)len) * 234 / 5;
> +}
> +
> +int
> +bar (unsigned int len)
> +{
> + return ((unsigned long)len) * 234 % 5;
> +}
> diff --git a/gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
> b/gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
> new file mode 100644
> index 00000000000..792d689395a
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mcpu=v3" } */
> +/* { dg-final { scan-assembler "global\t__divdi3" } } */
> +/* { dg-final { scan-assembler "global\t__moddi3" } } */
> +
> +int
> +foo (unsigned int len)
> +{
> + return ((long)len) * 234 / 5;
> +}
> +
> +int
> +bar (unsigned int len)
> +{
> + return ((long)len) * 234 % 5;
> +}
