On Fri, Jul 16, 2021 at 3:47 PM Alan Maguire alan.maguire@oracle.com wrote:

If data is packed, data structures can store it outside of usual boundaries. For example a 4-byte int can be stored on a unaligned boundary in a case like this:

struct s { char f1; int f2; } __attribute((packed));

...the int is stored at an offset of one byte. Some platforms have problems dereferencing data that is not aligned with its size, and code exists to handle most cases of this for BTF typed data display. However pointer display was missed, and a simple function to test if "ptr_is_aligned(data, data_sz)" would help clarify this code.

Suggested-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Alan Maguire alan.maguire@oracle.com

---

tools/lib/bpf/btf_dump.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index 929cf93..814a538 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -1654,6 +1654,11 @@ static int btf_dump_base_type_check_zero(struct btf_dump *d, return 0; }

+static bool ptr_is_aligned(const void *data, int data_sz) +{

•   return ((uintptr_t)data) % data_sz == 0;
  

+}

static int btf_dump_int_data(struct btf_dump *d, const struct btf_type *t, __u32 type_id, @@ -1672,7 +1677,7 @@ static int btf_dump_int_data(struct btf_dump *d, /* handle packed int data - accesses of integers not aligned on * int boundaries can cause problems on some platforms. */

•   if (((uintptr_t)data) % sz)
  

•   if (!ptr_is_aligned(data, sz))
            return btf_dump_bitfield_data(d, t, data, 0, 0);
  
    switch (sz) {
  

@@ -1739,7 +1744,7 @@ static int btf_dump_float_data(struct btf_dump *d, int sz = t->size;

    /* handle unaligned data; copy to local union */

•   if (((uintptr_t)data) % sz) {
  

•   if (!ptr_is_aligned(data, sz)) {
            memcpy(&fl, data, sz);
            flp = &fl;
    }
  

@@ -1892,12 +1897,29 @@ static int btf_dump_struct_data(struct btf_dump *d, return err; }

+union ptr_data {

•   unsigned int p;
  

•   unsigned long lp;
  

long can be 32-bit on 4-byte architectures, plus %llx implies long long (or we'll get another annoying warning from the compiler)

+};

static int btf_dump_ptr_data(struct btf_dump *d, const struct btf_type *t, __u32 id, const void *data) {

•   btf_dump_type_values(d, "%p", *(void **)data);
  

•   bool ptr_sz_matches = d->ptr_sz == sizeof(void *);
  

used just once and clear what it does, I inlined this, no point in separate variable

•   if (ptr_sz_matches && ptr_is_aligned(data, d->ptr_sz)) {
  

•           btf_dump_type_values(d, "%p", *(void **)data);
  

•   } else {
  

•           union ptr_data pt;
  

•           memcpy(&pt, data, d->ptr_sz);
  

•           if (d->ptr_sz == 4)
  

•                   btf_dump_type_values(d, "0x%x", pt.p);
  

•           else
  

•                   btf_dump_type_values(d, "0x%llx", pt.lp);
  

•   }
    return 0;
  

}

@@ -1910,7 +1932,7 @@ static int btf_dump_get_enum_value(struct btf_dump *d, int sz = t->size;

    /* handle unaligned enum value */

•   if (((uintptr_t)data) % sz) {
  

•   if (!ptr_is_aligned(data, sz)) {
            *value = (__s64)btf_dump_bitfield_get_data(d, t, data, 0, 0);
            return 0;
    }
  

-- 1.8.3.1

On Fri, Jul 16, 2021 at 3:47 PM Alan Maguire alan.maguire@oracle.com wrote:

Andrii reports:

"ppc64le arch doesn't like the %lld:

In file included from btf_dump.c:22: btf_dump.c: In function 'btf_dump_type_data_check_overflow': libbpf_internal.h:111:22: error: format '%lld' expects argument of type 'long long int', but argument 3 has type '__s64' {aka 'long int'} [-Werror=format=] 111 | libbpf_print(level, "libbpf: " fmt, ##__VA_ARGS__); \ | ^~~~~~~~~~ libbpf_internal.h:114:27: note: in expansion of macro '__pr' 114 | #define pr_warn(fmt, ...) __pr(LIBBPF_WARN, fmt, ##__VA_ARGS__) | ^~~~ btf_dump.c:1992:3: note: in expansion of macro 'pr_warn' 1992 | pr_warn("unexpected size [%lld] for id [%u]\n", | ^~~~~~~ btf_dump.c:1992:32: note: format string is defined here 1992 | pr_warn("unexpected size [%lld] for id [%u]\n", | ~~~^ | | | long long int | %ld

Cast to size_t and use %zu."

Quoting me isn't a great commit message by itself, tbh. Reworded.

Reported-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Alan Maguire alan.maguire@oracle.com

---

tools/lib/bpf/btf_dump.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index 814a538..e5fbfb8 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -2011,8 +2011,8 @@ static int btf_dump_type_data_check_overflow(struct btf_dump *d, __s64 size = btf__resolve_size(d->btf, id);

    if (size < 0 || size >= INT_MAX) {

•           pr_warn("unexpected size [%lld] for id [%u]\n",
  

•                   size, id);
  

•           pr_warn("unexpected size [%zu] for id [%u]\n",
  

•                   (size_t)size, id);
            return -EINVAL;
    }
  
  

-- 1.8.3.1

On Fri, Jul 16, 2021 at 3:47 PM Alan Maguire alan.maguire@oracle.com wrote:

By using the stack for this small structure, we avoid the need for freeing memory in error paths.

Suggested-by: Andrii Nakryiko andrii@kernel.org Signed-off-by: Alan Maguire alan.maguire@oracle.com

---

tools/lib/bpf/btf_dump.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c index e5fbfb8..bd8e005 100644 --- a/tools/lib/bpf/btf_dump.c +++ b/tools/lib/bpf/btf_dump.c @@ -2240,6 +2240,7 @@ int btf_dump__dump_type_data(struct btf_dump *d, __u32 id, const void *data, size_t data_sz, const struct btf_dump_type_data_opts *opts) {

•   struct btf_dump_data typed_dump = {};
    const struct btf_type *t;
    int ret;
  
  

@@ -2250,7 +2251,7 @@ int btf_dump__dump_type_data(struct btf_dump *d, __u32 id, if (!t) return libbpf_err(-ENOENT);

•   d->typed_dump = calloc(1, sizeof(struct btf_dump_data));
  

•   d->typed_dump = &typed_dump;
    if (!d->typed_dump)
            return libbpf_err(-ENOMEM);
  

can't happen, removed, please pay attention to the surrounding code

@@ -2269,7 +2270,5 @@ int btf_dump__dump_type_data(struct btf_dump *d, __u32 id,

    ret = btf_dump_dump_type_data(d, NULL, t, id, data, 0, 0);

•   free(d->typed_dump);
  

added resetting to NULL here, so that we don't have an accidental dangling pointers

    return libbpf_err(ret);

}

-- 1.8.3.1