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

[Daniel Borkmann]

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 <jakov.petrina at sartura.hr>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>

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)
>   {
>