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.

gcc/testsuite/ChangeLog:
	* gcc.target/bpf/atomic-cmpxchg-2.c: Adapted.
	* gcc.target/bpf/atomic-fetch-op-3.c: Adapted.
	* gcc.target/bpf/atomic-op-3.c: Adapted.
	* gcc.target/bpf/atomic-xchg-2.c: Adapted.
	* gcc.target/bpf/diag-sdiv.c: Adapted.
	* gcc.target/bpf/diag-smod.c: Adapted.

1 files changed, 21 insertions, 0 deletions

diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
index 4bfba28..8010801 100644
--- a/gcc/config/bpf/bpf.cc
+++ b/gcc/config/bpf/bpf.cc
@@ -746,6 +746,15 @@ 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);
 
@@ -765,6 +774,18 @@ 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.