From: Jean-Philippe Brucker jean-philippe@linaro.org
[ Upstream commit 901ee1d750f29a335423eeb9463c3ca461ca18c2 ]
The vmlinux.h generated from BTF is invalid when building drivers/phy/ti/phy-gmii-sel.c with clang:
vmlinux.h:61702:27: error: array type has incomplete element type ‘struct reg_field’ 61702 | const struct reg_field (*regfields)[3]; | ^~~~~~~~~
bpftool generates a forward declaration for this struct regfield, which compilers aren't happy about. Here's a simplified reproducer:
struct inner { int val; }; struct outer { struct inner (*ptr_to_array)[2]; } A;
After build with clang -> bpftool btf dump c -> clang/gcc: ./def-clang.h:11:23: error: array has incomplete element type 'struct inner' struct inner (*ptr_to_array)[2];
Member ptr_to_array of struct outer is a pointer to an array of struct inner. In the DWARF generated by clang, struct outer appears before struct inner, so when converting BTF of struct outer into C, bpftool issues a forward declaration to struct inner. With GCC the DWARF info is reversed so struct inner gets fully defined.
That forward declaration is not sufficient when compilers handle an array of the struct, even when it's only used through a pointer. Note that we can trigger the same issue with an intermediate typedef:
struct inner { int val; }; typedef struct inner inner2_t[2]; struct outer { inner2_t *ptr_to_array; } A;
Becomes:
struct inner; typedef struct inner inner2_t[2];
And causes:
./def-clang.h:10:30: error: array has incomplete element type 'struct inner' typedef struct inner inner2_t[2];
To fix this, clear through_ptr whenever we encounter an intermediate array, to make the inner struct part of a strong link and force full declaration.
Fixes: 351131b51c7a ("libbpf: add btf_dump API for BTF-to-C conversion") Signed-off-by: Jean-Philippe Brucker jean-philippe@linaro.org Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20210319112554.794552-2-jean-philippe@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/btf_dump.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index 2f9d685bd522..0911aea4cdbe 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -462,7 +462,7 @@ static int btf_dump_order_type(struct btf_dump *d, __u32 id, bool through_ptr) return err;
case BTF_KIND_ARRAY: - return btf_dump_order_type(d, btf_array(t)->type, through_ptr); + return btf_dump_order_type(d, btf_array(t)->type, false);
case BTF_KIND_STRUCT: case BTF_KIND_UNION: {