Re: [PATCH bpf] libbpf: Handle GCC built-in types for Arm NEON

On 8/10/20 2:28 PM, Jean-Philippe Brucker wrote:

When building Arm NEON (SIMD) code, GCC emits built-in types __PolyXX_t,
which are not recognized by Clang. This causes build failures when
including vmlinux.h generated from a kernel built with CONFIG_RAID6_PQ=y
and CONFIG_KERNEL_MODE_NEON. Emit typedefs for these built-in types,
based on the Clang definitions. poly64_t is unsigned long because it's
only defined for 64-bit Arm.

Including linux/kernel.h to use ARRAY_SIZE() incidentally redefined
max(), causing a build bug due to different types, hence the seemingly
unrelated change.

Reported-by: Jakov Petrina <redacted>
Signed-off-by: Jean-Philippe Brucker <redacted>

Looks like this was fixed here [0], but not available on older clang/LLVM
versions, right?

   [0] https://reviews.llvm.org/D79711

[...]

  
+static const char *builtin_types[][2] = {
+	/*
+	 * GCC emits typedefs to its internal __PolyXX_t types when compiling
+	 * Arm SIMD intrinsics. Alias them to the same standard types as Clang.
+	 */
+	{ "__Poly8_t",		"unsigned char" },
+	{ "__Poly16_t",		"unsigned short" },
+	{ "__Poly64_t",		"unsigned long" },
+	{ "__Poly128_t",	"unsigned __int128" },

In that above LLVM link [0], they typefdef this to signed types ... which one
is correct now?

   // For now, signedness of polynomial types depends on target
   OS << "#ifdef __aarch64__\n";
   OS << "typedef uint8_t poly8_t;\n";
   OS << "typedef uint16_t poly16_t;\n";
   OS << "typedef uint64_t poly64_t;\n";
   OS << "typedef __uint128_t poly128_t;\n";
   OS << "#else\n";
   OS << "typedef int8_t poly8_t;\n";
   OS << "typedef int16_t poly16_t;\n";
   OS << "typedef int64_t poly64_t;\n";
   OS << "#endif\n";

+};
+
+static void btf_dump_emit_int_def(struct btf_dump *d, __u32 id,
+				  const struct btf_type *t)
+{
+	const char *name = btf_dump_type_name(d, id);
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(builtin_types); i++) {
+		if (strcmp(name, builtin_types[i][0]) == 0) {
+			btf_dump_printf(d, "typedef %s %s;\n\n",
+					builtin_types[i][1], name);
+			break;
+		}
+	}
+}
+
  static void btf_dump_emit_enum_fwd(struct btf_dump *d, __u32 id,
  				   const struct btf_type *t)
  {

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