Re: [PAHOLE v5 5/5] tests: Add btf_type_tag ordering test

On Wed Jun 17, 2026 at 8:57 PM EDT, Vineet Gupta wrote:
> From: Alan Maguire <[email protected]>
>
> Add a test that compiles a pointer carrying two btf_type_tags
> (__tag(outer) __tag(inner)) and checks the BTF that pahole emits to
> ensure the tag chain is PTR -> TYPE_TAG inner -> TYPE_TAG outer ->
> struct sample, i.e. the innermost tag is closest to the pointer.
>
> This exercises the type_tag ordering for both encodings: LLVM emits the
> annotations as child DIEs in source order (reversed when building the
> tag list), while GCC chains them via DW_AT_GNU_annotation already in BTF
> order. The test runs with gcc and clang when they support btf_type_tag,
> and is skipped when bpftool is unavailable.
>
> Signed-off-by: Alan Maguire <[email protected]>
> Signed-off-by: Vineet Gupta <[email protected]>
> ---

Reviewed-by: Emil Tsalapatis <[email protected]>

>  tests/btf_type_tag_order.sh | 179 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 179 insertions(+)
>  create mode 100755 tests/btf_type_tag_order.sh
>
> diff --git a/tests/btf_type_tag_order.sh b/tests/btf_type_tag_order.sh
> new file mode 100755
> index 000000000000..09d1ac346000
> --- /dev/null
> +++ b/tests/btf_type_tag_order.sh
> @@ -0,0 +1,179 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +# Check that pahole preserves btf_type_tag order when emitting BTF from DWARF.
> +
> +source test_lib.sh
> +
> +outdir=$(make_tmpdir)
> +
> +# Comment this out to save test data.
> +trap cleanup EXIT
> +
> +title_log "Check BTF type tag order."
> +
> +GCC=${GCC:-gcc}
> +CLANG=${CLANG:-clang}
> +PAHOLE=${PAHOLE:-pahole}
> +BPFTOOL=${BPFTOOL:-bpftool}
> +
> +if ! command -v "$BPFTOOL" > /dev/null; then
> +	info_log "skip: bpftool not available"
> +	test_skip
> +fi
> +
> +compiler_has_btf_type_tag()
> +{
> +	local compiler=$1
> +
> +	if ! command -v "$compiler" > /dev/null; then
> +		return 1
> +	fi
> +
> +	"$compiler" -x c -E -P - <<'EOF' 2>/dev/null | grep -qx 1
> +#ifndef __has_attribute
> +#define __has_attribute(x) 0
> +#endif
> +#if __has_attribute(btf_type_tag)
> +1
> +#else
> +0
> +#endif
> +EOF
> +}
> +
> +use_gcc=0
> +if compiler_has_btf_type_tag "$GCC"; then
> +	use_gcc=1
> +fi
> +
> +use_clang=0
> +if compiler_has_btf_type_tag "$CLANG"; then
> +	use_clang=1
> +fi
> +
> +if [ "$use_gcc" -eq 0 ] && [ "$use_clang" -eq 0 ]; then
> +	error_log "Need gcc or clang with btf_type_tag support for test $0"
> +	test_fail
> +fi
> +
> +src=$(cat <<EOF
> +#define __tag(x) __attribute__((btf_type_tag(#x)))
> +
> +struct sample {
> +	int value;
> +};
> +
> +struct sample __tag(outer) __tag(inner) *global_ptr;
> +
> +EOF
> +)
> +
> +check_type_tag_order()
> +{
> +	local btf=$1
> +	local dump
> +
> +	if ! dump=$("$BPFTOOL" btf dump file "$btf"); then
> +		return 1
> +	fi
> +
> +	printf '%s\n' "$dump" | awk '
> +	function parse_id(line, m) {
> +		if (match(line, /^\[([0-9]+)\]/, m))
> +			return m[1]
> +		return 0
> +	}
> +	function parse_name(line, m) {
> +		if (match(line, /\047([^\047]*)\047/, m))
> +			return m[1]
> +		return ""
> +	}
> +	function parse_type(line, m) {
> +		if (match(line, /type_id=([0-9]+)/, m))
> +			return m[1]
> +		return 0
> +	}
> +	function check_ptr(ptr, id, tags, seen) {
> +		id = type[ptr]
> +		while (id != 0 && !seen[id]) {
> +			seen[id] = 1
> +			if (kind[id] == "TYPE_TAG") {
> +				tags = tags (tags == "" ? "" : " -> ") name[id]
> +				id = type[id]
> +				continue
> +			}
> +			if (kind[id] == "STRUCT" && name[id] == "sample") {
> +				if (tags == "inner -> outer")
> +					exit 0
> +				candidates = candidates (candidates == "" ? "" : ", ") tags
> +			}
> +			return
> +		}
> +	}
> +	/^\[[0-9]+\]/ {
> +		id = parse_id($0)
> +		kind[id] = $2
> +		name[id] = parse_name($0)
> +		type[id] = parse_type($0)
> +		if (kind[id] == "PTR")
> +			ptrs[++nr_ptrs] = id
> +	}
> +	END {
> +		for (i = 1; i <= nr_ptrs; i++)
> +			check_ptr(ptrs[i])
> +		if (candidates != "") {
> +			print "type tag order mismatch; expected inner -> outer, found " candidates > "/dev/stderr"
> +			exit 1
> +		}
> +		print "could not find tagged pointer to struct sample" > "/dev/stderr"
> +		exit 1
> +	}'
> +}
> +
> +run_test()
> +{
> +	local compiler=$1
> +	local tmpobj=$2
> +	local btf=$3
> +
> +	info_log "Testing with $compiler"
> +
> +	if ! echo "$src" | "$compiler" -g -c -x c -o "$tmpobj" - 2>/dev/null; then
> +		error_log "Could not compile type tag order test with $compiler"
> +		return 1
> +	fi
> +
> +	if ! "$PAHOLE" --btf_features=+type_tag --btf_encode_detached="$btf" "$tmpobj" 2>/dev/null; then
> +		error_log "Could not encode BTF for $tmpobj"
> +		return 1
> +	fi
> +
> +	if check_type_tag_order "$btf"; then
> +		info_log "  passed"
> +		return 0
> +	fi
> +
> +	error_log "BTF type tag order does not match expected order ($compiler)"
> +	return 1
> +}
> +
> +failed=0
> +
> +if [ "$use_gcc" -eq 1 ]; then
> +	tmpobj=$(make_tmpobj)
> +	btf=${tmpobj%.o}.btf
> +	run_test "$GCC" "$tmpobj" "$btf" || failed=1
> +fi
> +
> +if [ "$use_clang" -eq 1 ]; then
> +	tmpobj=$(make_tmpobj)
> +	btf=${tmpobj%.o}.btf
> +	run_test "$CLANG" "$tmpobj" "$btf" || failed=1
> +fi
> +
> +if [ "$failed" -eq 0 ]; then
> +	test_pass
> +else
> +	test_fail
> +fi