Hi Cuper.
OK. Thanks for the patch.
> Hi everyone,
>
> The attached patch is a temporary solution for the lack of proper linker
> and external library linking of the eBPF platform.
> Any calls created by the compiler, that would usually be defined within
> libgcc, will endup being undefined in bpftool, when GCC the compiled
> code is passed.
>
> This patch anticipates that error to the compiler, by verifiying if
> any of those calls are being generated, and reporting as an error.
>
> Looking forward to your comments.
>
> Cheers,
> Cupertino
>
> commit c2110ae497c7ff83c309f172bc265973652b760d
> Author: Cupertino Miranda <cupertino.mira...@oracle.com>
> Date: Thu Nov 23 22:28:01 2023 +0000
>
> This patch enables errors when external calls are created.
>
> When architectural limitations or usage of builtins implies the compiler
> to create function calls to external libraries that implement the
> functionality, GCC will now report an error claiming that this function
> calls are not compatible with eBPF target.
> Examples of those are the usage of __builtin_memmove and a sign division
> in BPF ISA v3 or below that will require to call __divdi3.
> This is currently an eBPF limitation which does not support linking of
> object files but rather "raw" non linked ones. Those object files are
> loaded and relocated by libbpf and the kernel.
>
> gcc/ChangeLog:
> * config/bpf/bpf.cc (bpf_output_call): Report error in case the
> function call is for a builtin.
> (bpf_external_libcall): Added target hook to detect and report
> error when other external calls that are not builtins.
>
> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
> index 0c9d5257c384..1c84113055b1 100644
> --- a/gcc/config/bpf/bpf.cc
> +++ b/gcc/config/bpf/bpf.cc
> @@ -744,6 +744,15 @@ bpf_output_call (rtx target)
> xops[0] = GEN_INT (TREE_INT_CST_LOW (TREE_VALUE (attr_args)));
> output_asm_insn ("call\t%0", xops);
> }
> + else if (fndecl_built_in_p (decl))
> + {
> + /* For now lets report this as an error while we are not able to
> + link eBPF object files. In particular with libgcc. */
> + tree name = DECL_NAME (decl);
> + error ("call to external builtin %s in function, which is not
> supported by "
> + "eBPF", name != NULL_TREE ? IDENTIFIER_POINTER (name) :
> "(anon)");
> + output_asm_insn ("call 0", NULL);
> + }
> else
> output_asm_insn ("call\t%0", &target);
>
> @@ -763,6 +772,18 @@ bpf_output_call (rtx target)
> return "";
> }
>
> +static void
> +bpf_external_libcall (rtx fun)
> +{
> + tree decl = SYMBOL_REF_DECL (fun);
> + tree name = DECL_NAME (decl);
> + error ("call to external libcall %s in function, which is not supported by
> "
> + "eBPF", name != NULL_TREE ? IDENTIFIER_POINTER (name) : "(anon)");
> +}
> +
> +#undef TARGET_ASM_EXTERNAL_LIBCALL
> +#define TARGET_ASM_EXTERNAL_LIBCALL bpf_external_libcall
> +
> /* Print register name according to assembly dialect. In normal
> syntax registers are printed like %rN where N is the register
> number.
> diff --git a/gcc/testsuite/gcc.target/bpf/atomic-cmpxchg-2.c
> b/gcc/testsuite/gcc.target/bpf/atomic-cmpxchg-2.c
> index 4036570ac601..fec720584e48 100644
> --- a/gcc/testsuite/gcc.target/bpf/atomic-cmpxchg-2.c
> +++ b/gcc/testsuite/gcc.target/bpf/atomic-cmpxchg-2.c
> @@ -6,7 +6,7 @@ foo (int *p, int *expected, int desired)
> {
> return __atomic_compare_exchange (p, expected, &desired, 0,
> __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
> -}
> +} /* { dg-error "call to external builtin" } */
>
> int
> foo64 (long *p, long *expected, long desired)
> diff --git a/gcc/testsuite/gcc.target/bpf/atomic-fetch-op-3.c
> b/gcc/testsuite/gcc.target/bpf/atomic-fetch-op-3.c
> index 044a2f76474b..ea1b8e48928a 100644
> --- a/gcc/testsuite/gcc.target/bpf/atomic-fetch-op-3.c
> +++ b/gcc/testsuite/gcc.target/bpf/atomic-fetch-op-3.c
> @@ -9,7 +9,7 @@ long
> test_atomic_fetch_add (long x)
> {
> return __atomic_fetch_add (&val, x, __ATOMIC_ACQUIRE);
> -}
> +} /* { dg-error "call to external builtin" } */
>
> long
> test_atomic_fetch_sub (long x)
> diff --git a/gcc/testsuite/gcc.target/bpf/atomic-op-3.c
> b/gcc/testsuite/gcc.target/bpf/atomic-op-3.c
> index b2ce28926347..fefafd6b748f 100644
> --- a/gcc/testsuite/gcc.target/bpf/atomic-op-3.c
> +++ b/gcc/testsuite/gcc.target/bpf/atomic-op-3.c
> @@ -20,7 +20,7 @@ void
> test_atomic_and (int x)
> {
> __atomic_and_fetch (&val, x, __ATOMIC_ACQUIRE);
> -}
> +} /* { dg-error "call to external builtin" } */
>
> void
> test_atomic_nand (int x)
> diff --git a/gcc/testsuite/gcc.target/bpf/atomic-xchg-2.c
> b/gcc/testsuite/gcc.target/bpf/atomic-xchg-2.c
> index 3b6324e966b8..eab695bf388c 100644
> --- a/gcc/testsuite/gcc.target/bpf/atomic-xchg-2.c
> +++ b/gcc/testsuite/gcc.target/bpf/atomic-xchg-2.c
> @@ -7,7 +7,7 @@ int foo (int *p, int *new)
> int old;
> __atomic_exchange (p, new, &old, __ATOMIC_RELAXED);
> return old;
> -}
> +} /* { dg-error "call to external builtin" } */
>
> int foo64 (long *p, long *new)
> {
> diff --git a/gcc/testsuite/gcc.target/bpf/diag-sdiv.c
> b/gcc/testsuite/gcc.target/bpf/diag-sdiv.c
> index c48bbf03df97..c3332558e7d2 100644
> --- a/gcc/testsuite/gcc.target/bpf/diag-sdiv.c
> +++ b/gcc/testsuite/gcc.target/bpf/diag-sdiv.c
> @@ -7,6 +7,6 @@ foo ()
> {
> signed int x = 5;
> signed int y = 2;
> - signed int z = x / y;
> + signed int z = x / y; /* { dg-error "call to external libcall" } */
> }
> /* { dg-final { scan-assembler-not "sdiv(32)?\t%r" } } */
> diff --git a/gcc/testsuite/gcc.target/bpf/diag-smod.c
> b/gcc/testsuite/gcc.target/bpf/diag-smod.c
> index d3df308217f3..25bcb1e4ffdb 100644
> --- a/gcc/testsuite/gcc.target/bpf/diag-smod.c
> +++ b/gcc/testsuite/gcc.target/bpf/diag-smod.c
> @@ -7,6 +7,6 @@ foo ()
> {
> signed int x = 5;
> signed int y = 2;
> - signed int z = x % y;
> + signed int z = x % y; /* { dg-error "call to external libcall" } */
> }
> /* { dg-final { scan-assembler-not "smod(32)?\t%r" } } */
