Re: [PATCH 1/2] libtraceevent: Add loading of BTF to the tep handle

On 04-08-2025 17:07, Douglas Raillard wrote:
> 
> 
> On 31-07-2025 19:52, Steven Rostedt wrote:
>> From: "Steven Rostedt (Google)" <[email protected]>
>>
>> Add loading of the BTF file /sys/kernel/btf/vmlinux into the tep_handler and
>> then use it to format the function tracer if it has arguments:
>>
>>      cat-33501 [005] ..... 136155.767950: function:             __x64_sys_execve(regs=0xffffc9000e3eff58)
>>      cat-33501 [005] ..... 136155.767951: function:                getname_flags(filename=0x7ffe7d33f3d0, flags=0)
>>      cat-33501 [005] ..... 136155.767951: function:                getname_flags.part.0(7ffe7d33f3d0, 0, 0, 0, 0, 0)
>>      cat-33501 [005] ..... 136155.767951: function:                   kmem_cache_alloc_noprof(s=0xffff8881001d3800, gfpflags=0xcc0)
>>      cat-33501 [005] ..... 136155.767951: function:                      fs_reclaim_acquire(gfp_mask=0xcc0)
>>      cat-33501 [005] ..... 136155.767952: function:                      fs_reclaim_release(gfp_mask=0xcc0)
>>      cat-33501 [005] ..... 136155.767953: function:                      kmemleak_alloc(ptr=0xffff8881114a0000, size=0x1000, min_count=1, gfp=0xcc0)
>>      cat-33501 [005] ..... 136155.767953: function:                      __create_object(ptr=0xffff8881114a0000, size=0x1000, min_count=1, gfp=0xcc0, objflags=0x0)
>>      cat-33501 [005] ..... 136155.767954: function:                         __alloc_object(gfp=0xcc0)
>>      cat-33501 [005] ..... 136155.767954: function:                            kmem_cache_alloc_noprof(s=0xffff888100045700, gfpflags=0x92cc0)
>>      cat-33501 [005] ..... 136155.767954: function:                      fs_reclaim_acquire(gfp_mask=0x92cc0)
>>      cat-33501 [005] ..... 136155.767955: function:                      fs_reclaim_release(gfp_mask=0x92cc0)
>>
>> Signed-off-by: Steven Rostedt (Google) <[email protected]>
>> ---
>>   include/traceevent/event-parse.h |   5 +
>>   plugins/plugin_function.c        |  15 +-
>>   src/Makefile                     |   1 +
>>   src/event-parse-local.h          |   6 +
>>   src/event-parse.c                |   2 +
>>   src/trace-btf.c                  | 449 +++++++++++++++++++++++++++++++
>>   6 files changed, 468 insertions(+), 10 deletions(-)
>>   create mode 100644 src/trace-btf.c
>>
>> diff --git a/include/traceevent/event-parse.h b/include/traceevent/event-parse.h
>> index d3ce0a43a8fc..ebfc2c7abac2 100644
>> --- a/include/traceevent/event-parse.h
>> +++ b/include/traceevent/event-parse.h
>> @@ -580,6 +580,11 @@ int tep_get_ref(struct tep_handle *tep);
>>   struct kbuffer *tep_kbuffer(struct tep_handle *tep);
>> +/* BTF */
>> +int tep_load_btf(struct tep_handle *tep, void *raw_data, size_t data_size);
>> +int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
>> +               int nmem, int size, const char *func);
>> +
>>   /* for debugging */
>>   void tep_print_funcs(struct tep_handle *tep);
>>   void tep_print_printk(struct tep_handle *tep);
>> diff --git a/plugins/plugin_function.c b/plugins/plugin_function.c
>> index a337446e3462..379fc3ad0ffd 100644
>> --- a/plugins/plugin_function.c
>> +++ b/plugins/plugin_function.c
>> @@ -135,10 +135,9 @@ static void show_function(struct trace_seq *s, struct tep_handle *tep,
>>   /* Returns true if it printed args, otherwise it returns false */
>>   static bool print_args(struct trace_seq *s, struct tep_event *event,
>> -               struct tep_record *record)
>> +               struct tep_record *record, const char *func)
>>   {
>>       struct tep_format_field *field;
>> -    unsigned long arg;
>>       void *args;
>>       int len;
>> @@ -156,12 +155,8 @@ static bool print_args(struct trace_seq *s, struct tep_event *event,
>>       trace_seq_putc(s, '(');
>> -    for (int i = 0; i < len; i += sizeof(long), args += sizeof(long)) {
>> -        memcpy(&arg, args, sizeof(long));
>> -        trace_seq_printf(s, "%lx", arg);
>> -        if (i + sizeof(long) < len)
>> -            trace_seq_puts(s, ", ");
>> -    }
>> +    tep_btf_print_args(event->tep, s, args, len / sizeof(long), sizeof(long), func);
>> +
>>       trace_seq_putc(s, ')');
>>       return true;
>>   }
>> @@ -196,7 +191,7 @@ static int function_handler(struct trace_seq *s, struct tep_record *record,
>>       else
>>           trace_seq_printf(s, "0x%llx", function);
>> -    print_args(s, event, record);
>> +    print_args(s, event, record, func);
>>       if (ftrace_parent->set) {
>>           trace_seq_printf(s, " <-- ");
>> @@ -281,7 +276,7 @@ trace_stack_handler(struct trace_seq *s, struct tep_record *record,
>>   static int
>>   trace_raw_data_handler(struct trace_seq *s, struct tep_record *record,
>> -            struct tep_event *event, void *context)
>> +               struct tep_event *event, void *context)
>>   {
>>       struct tep_format_field *field;
>>       unsigned long long id;
>> diff --git a/src/Makefile b/src/Makefile
>> index 53bb570182d2..1ff669ce8deb 100644
>> --- a/src/Makefile
>> +++ b/src/Makefile
>> @@ -11,6 +11,7 @@ OBJS += parse-filter.o
>>   OBJS += parse-utils.o
>>   OBJS += tep_strerror.o
>>   OBJS += trace-seq.o
>> +OBJS += trace-btf.o
>>   OBJS := $(OBJS:%.o=$(bdir)/%.o)
>>   DEPS := $(OBJS:$(bdir)/%.o=$(bdir)/.%.d)
>> diff --git a/src/event-parse-local.h b/src/event-parse-local.h
>> index d9e9faf649d1..50bc4d87bbe6 100644
>> --- a/src/event-parse-local.h
>> +++ b/src/event-parse-local.h
>> @@ -14,6 +14,7 @@ struct func_list;
>>   struct event_handler;
>>   struct func_resolver;
>>   struct tep_plugins_dir;
>> +struct tep_btf;
>>   #define __hidden __attribute__((visibility ("hidden")))
>> @@ -89,6 +90,8 @@ struct tep_handle {
>>       const char *input_buf;
>>       unsigned long long input_buf_ptr;
>>       unsigned long long input_buf_siz;
>> +
>> +    struct tep_btf *btf;
>>   };
>>   enum tep_print_parse_type {
>> @@ -124,4 +127,7 @@ const char *tep_get_input_buf(struct tep_handle *tep);
>>   enum tep_event_type tep_read_token(struct tep_handle *tep, char **tok);
>>   void tep_free_token(char *tok);
>> +/* BTF routines */
>> +void tep_btf_free(struct tep_btf *btf);
>> +
>>   #endif /* _PARSE_EVENTS_INT_H */
>> diff --git a/src/event-parse.c b/src/event-parse.c
>> index aa16d83bb2ad..730f25c92110 100644
>> --- a/src/event-parse.c
>> +++ b/src/event-parse.c
>> @@ -8726,6 +8726,8 @@ void tep_free(struct tep_handle *tep)
>>       free(tep->func_resolver);
>>       tep_free_plugin_paths(tep);
>> +    tep_btf_free(tep->btf);
>> +
>>       free(tep);
>>   }
>> diff --git a/src/trace-btf.c b/src/trace-btf.c
>> new file mode 100644
>> index 000000000000..79c5d6c93327
>> --- /dev/null
>> +++ b/src/trace-btf.c
>> @@ -0,0 +1,449 @@
>> +// SPDX-License-Identifier: LGPL-2.1
>> +/*
>> + * Copyright (C) 2025 Google, Steven Rostedt <[email protected]>
>> + *
>> + */
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <stdbool.h>
>> +
>> +#include <linux/btf.h>
>> +
>> +#include "event-parse.h"
>> +#include "event-utils.h"
>> +#include "event-parse-local.h"
>> +
>> +struct btf_header;
>> +struct btf_type;
>> +
>> +struct tep_btf {
>> +    struct btf_header    *hdr;
>> +    const char        *strings;
>> +    struct btf_type        **types;
>> +    unsigned long        nr_types;
>> +    struct btf_type        **funcs;
>> +    unsigned long        nr_funcs;
>> +    void            *data;
>> +    size_t            raw_size;
>> +    void            *raw_data;
>> +};
>> +
>> +#define REALLOC_SIZE (1 << 10)
>> +#define REALLOC_MASK (REALLOC_SIZE - 1)
>> +
>> +static const char *btf_name(struct tep_btf *btf, int off)
>> +{
>> +    if (off < btf->hdr->str_len)
> 
> That assumes the input is well-behaved and str_len is set to the actual length of
> the strings data, but it could be anything. tep_btf_init() should check that
> btf->hdr->strings + btf->hdr->str_len point inside the provided data.
> 
>> +        return btf->strings + off;> +    return "";
>> +}
>> +
>> +/* List taken from the Linux kernel */
>> +static const char * const btf_kind_str[NR_BTF_KINDS] = {
>> +    [BTF_KIND_UNKN]        = "UNKNOWN",
>> +    [BTF_KIND_INT]        = "INT",
>> +    [BTF_KIND_PTR]        = "PTR",
>> +    [BTF_KIND_ARRAY]    = "ARRAY",
>> +    [BTF_KIND_STRUCT]    = "STRUCT",
>> +    [BTF_KIND_UNION]    = "UNION",
>> +    [BTF_KIND_ENUM]        = "ENUM",
>> +    [BTF_KIND_FWD]        = "FWD",
>> +    [BTF_KIND_TYPEDEF]    = "TYPEDEF",
>> +    [BTF_KIND_VOLATILE]    = "VOLATILE",
>> +    [BTF_KIND_CONST]    = "CONST",
>> +    [BTF_KIND_RESTRICT]    = "RESTRICT",
>> +    [BTF_KIND_FUNC]        = "FUNC",
>> +    [BTF_KIND_FUNC_PROTO]    = "FUNC_PROTO",
>> +    [BTF_KIND_VAR]        = "VAR",
>> +    [BTF_KIND_DATASEC]    = "DATASEC",
>> +    [BTF_KIND_FLOAT]    = "FLOAT",
>> +    [BTF_KIND_DECL_TAG]    = "DECL_TAG",
>> +    [BTF_KIND_TYPE_TAG]    = "TYPE_TAG",
>> +    [BTF_KIND_ENUM64]    = "ENUM64",
>> +};
>> +
>> +static const char *btf_type_str(const struct btf_type *t)
>> +{
>> +    return btf_kind_str[BTF_INFO_KIND(t->info)];
>> +}
>> +
>> +static int insert_type(struct btf_type ***types, unsigned long *cnt, struct btf_type *type)
>> +{
>> +    unsigned long nr_types = *cnt;
>> +        struct btf_type **array = *types;
>> +
>> +        if (!(nr_types & REALLOC_MASK)) {
>> +                int size = nr_types + REALLOC_SIZE;
>> +
>> +                array = realloc(array, sizeof(struct btf_type *) * size);
>> +                if (!array) {
>> +            tep_warning("Failed to alloct memory for new type");
>> +            return -1;
>> +        }
>> +                *types = array;
>> +        }
>> +
>> +        array[nr_types++] = type;
>> +    *cnt = nr_types;
>> +    return 0;
>> +}
>> +
>> +static int add_type(struct tep_btf *btf, struct btf_type *type)
>> +{
>> +    return insert_type(&btf->types, &btf->nr_types, type);
>> +}
>> +
>> +static int add_func(struct tep_btf *btf, struct btf_type *type)
>> +{
>> +    return insert_type(&btf->funcs, &btf->nr_funcs, type);
>> +}
>> +
>> +static int btf_type_size(struct btf_type *type)
>> +{
>> +    int kind = BTF_INFO_KIND(type->info);
>> +    int size = sizeof(*type);
>> +
>> +    switch (kind) {
>> +    case BTF_KIND_INT:
>> +        return size + sizeof(int);
>> +    case BTF_KIND_VAR:
>> +        return size + sizeof(struct btf_var);
>> +    case BTF_KIND_ARRAY:
>> +        return size + sizeof(struct btf_array);
>> +    case BTF_KIND_DECL_TAG:
>> +        return size + sizeof(struct btf_decl_tag);
>> +    case BTF_KIND_ENUM:
>> +        return size + sizeof(struct btf_enum) * BTF_INFO_VLEN(type->info);
>> +    case BTF_KIND_ENUM64:
>> +        return size + sizeof(struct btf_enum64) * BTF_INFO_VLEN(type->info);
>> +    case BTF_KIND_STRUCT:
>> +    case BTF_KIND_UNION:
>> +        return size + sizeof(struct btf_member) * BTF_INFO_VLEN(type->info);
>> +    case BTF_KIND_FUNC_PROTO:
>> +        return size + sizeof(struct btf_param) * BTF_INFO_VLEN(type->info);
>> +    case BTF_KIND_DATASEC:
>> +        return size + sizeof(struct btf_var_secinfo) * BTF_INFO_VLEN(type->info);
>> +    case BTF_KIND_PTR:
>> +    case BTF_KIND_FWD:
>> +    case BTF_KIND_TYPEDEF:
>> +    case BTF_KIND_VOLATILE:
>> +    case BTF_KIND_CONST:
>> +    case BTF_KIND_RESTRICT:
>> +    case BTF_KIND_TYPE_TAG:
>> +    case BTF_KIND_FUNC:
>> +    case BTF_KIND_FLOAT:
>> +        return size;
>> +    }
>> +    return -1;
>> +}
>> +
>> +static int cmp_funcs(const void *A, const void *B, void *data)
>> +{
>> +    struct tep_btf *btf = data;
>> +    const struct btf_type *a = *(const struct btf_type **)A;
>> +    const struct btf_type *b = *(const struct btf_type **)B;
>> +    const char *name_a = btf_name(btf, a->name_off);
>> +    const char *name_b = btf_name(btf, b->name_off);
>> +
>> +    return strcmp(name_a, name_b);
>> +}
>> +
>> +struct tcmd_search {
>> +    struct tep_btf        *btf;
>> +    const char        *name;
>> +};
>> +
>> +static int cmp_key_func(const void *A, const void *B)
>> +{
>> +    const struct tcmd_search *key = A;
>> +    const struct btf_type *b = *(const struct btf_type **)B;
>> +    const char *name_b = btf_name(key->btf, b->name_off);
>> +
>> +    return strcmp(key->name, name_b);
>> +}
>> +
>> +static struct btf_type *tep_btf_find_func(struct tep_btf *btf, const char *name)
>> +{
>> +    struct tcmd_search tsearch;
>> +    struct btf_type **t;
>> +
>> +    if (!btf || !name)
>> +        return NULL;
>> +
>> +    tsearch.btf = btf;
>> +    tsearch.name = name;
>> +
>> +    t = bsearch(&tsearch, btf->funcs, btf->nr_funcs, sizeof(btf->funcs[0]),
>> +            cmp_key_func);
>> +
>> +    return t ? *t : NULL;
>> +}
>> +
>> +static int load_types(struct tep_btf *btf)
>> +{
>> +    struct btf_type *type;
>> +    void *start, *end;
>> +    int size;
>> +
>> +    start = btf->data + btf->hdr->type_off;
>> +    end = start + btf->hdr->type_len;
> 
> Those should also be validated.
> 
>> +
>> +    if (end > btf->raw_data + btf->raw_size)
>> +        return -1;
>> +
>> +    for (type = start; (void *)type < end;) {
>> +        if (add_type(btf, type))
>> +            return -1;
>> +        if (BTF_INFO_KIND(type->info) == BTF_KIND_FUNC) {
>> +            if (add_func(btf, type))
>> +                return -1;
>> +        }
>> +        size = btf_type_size(type);
>> +        if (size < 0) {
>> +            tep_warning("Invalid type %d\n", BTF_INFO_KIND(type->info));
>> +            return -1;
>> +        }
>> +        type = (void *)type + size;
>> +    }
>> +
>> +    qsort_r(btf->funcs, btf->nr_funcs, sizeof(btf->funcs[0]), cmp_funcs, btf);
>> +    return 0;
>> +}
>> +
>> +__hidden void tep_btf_free(struct tep_btf *btf)
>> +{
>> +    if (!btf)
>> +        return;
>> +
>> +    free((void *)btf->strings);
>> +    free(btf->types);
>> +    free(btf->funcs);
>> +    free(btf->raw_data);
>> +}
>> +
>> +/** tep_btf_init - Initialize btf with raw data
>> + * @raw_data: Allocated data to use for BTF (/sys/kernel/btf/vmlinux)
>> + * @data_size: The amount of data in @raw_data
>> + *
>> + * The @raw_data ownership belongs to this function when called.
>> + * It must be allocated by the glibc allocator as it will be freed
>> + * when the BTF descriptor is freed. It will not be freed if this
>> + * function returns failure (NULL).
>> + *
>> + * Returns: On success it returns the BTF descriptor, and he @raw_data
>> + *   will now be apart of it (it will be freed by tep_btf_free().
>> + *   On failure it returns NULL, and the @raw_data is NOT freed.
>> + */
>> +static struct tep_btf *tep_btf_init(void *raw_data, size_t data_size)
>> +{
>> +    struct tep_btf *btf;
>> +
>> +    btf = calloc(1, sizeof(*btf));
>> +    if (!btf)
>> +        return NULL;
>> +
>> +    btf->raw_data = raw_data;
>> +    btf->raw_size = data_size;
>> +    btf->hdr = raw_data;
>> +    if (btf->hdr->hdr_len < sizeof(*btf->hdr)) {
>> +        tep_warning("Header (%d) smaller than expected header %zd",
>> +                btf->hdr->hdr_len, sizeof(*btf->hdr));
>> +        goto fail;
>> +    }
> 
> btf->hdr->magic and btf->hdr->version should be checked to catch any garbage input and
> breaking change to the format:
> 
>    The magic is 0xeB9F, which has different encoding for big and little endian systems,
>    and can be used to test whether BTF is generated for big- or little-endian target.
> 
>    https://docs.kernel.org/bpf/btf.html#btf-type-and-string-encoding
> 
>> +
>> +    btf->data = btf->raw_data + btf->hdr->hdr_len;
>> +
>> +    btf->strings = btf->data + btf->hdr->str_off;
> 
> This pointer crafting without input validation looks like a CVE-in-waiting.
> Using libbpf would indeed add a dependency, but it seems those checks are taken care of:
> https://github.com/libbpf/libbpf/blob/58dd1f58b57294b2e59482245b29e46f1812b82d/src/btf.c#L258
> 
> This is not to say libbpf is perfect, but there also seem to be some people running fuzzers on it
> so issues of this kind have a higher chance of getting found, e.g.
> https://nvd.nist.gov/vuln/detail/CVE-2025-29481
> 
> I suppose there is no silver bullet here, as adding dependencies to a C program is a pain
> as it breaks downstream build recipes ...
> 
> Alternatively, the Rust parser has no BTF-related buffer issue, but that's because it does not
> implement anything BTF-related yet :)

Another thing that libbpf checks is that the type data are aligned on 4 bytes:
https://github.com/libbpf/libbpf/blob/58dd1f58b57294b2e59482245b29e46f1812b82d/src/btf.c#L269

This is required for soundly casting void* to the types in btf.h, which seem to be written with
that assumption in mind even though it's not explicitly documented:

   struct btf_enum64 {
       __u32   name_off;
       __u32   val_lo32;
       __u32   val_hi32;
   };

libtraceevent requires an allocation from the libc which already guarantees that alignment but having an explicit
check is not a bad idea in case that were to change.

> 
>> +    printf("str len = %d\n", btf->hdr->str_len);
>> +
>> +    if (load_types(btf) < 0)
>> +        goto fail;
>> +
>> +    return btf;
>> + fail:
>> +    btf->raw_data = NULL;
>> +    tep_btf_free(btf);
>> +    return NULL;
>> +}
>> +
>> +/**
>> + * tep_load_btf - Load BTF information into a tep handle
>> + * @tep: The tep handle to load the BTF info into
>> + * @raw_data: The raw data containing the BTF file
>> + * @data_size: The amount of data in @raw_data
>> + *
>> + * Initializes BTF into the @tep handle. If it had already had BTF
>> + * loaded, it will free the previous BTF and recreate it from @raw_data.
>> + *
>> + * Returns: 0 on success and -1 on failure.
>> + */
>> +int tep_load_btf(struct tep_handle *tep, void *raw_data, size_t data_size)
>> +{
>> +    /* If btf was already loaded, free it */
>> +    tep_btf_free(tep->btf);
>> +
>> +    tep->btf = tep_btf_init(raw_data, data_size);
>> +    if (!tep->btf)
>> +        return -1;
>> +    return 0;
>> +}
>> +
>> +static struct btf_type *btf_get_type(struct tep_btf *btf, int id)
>> +{
>> +    if (!id || id > btf->nr_types)
>> +        return NULL;
>> +
>> +    return btf->types[id - 1];
>> +}
>> +
>> +static struct btf_type *btf_skip_modifiers(struct tep_btf *btf, int id)
>> +{
>> +    struct btf_type *t = btf_get_type(btf, id);
>> +
>> +    for (;;) {
>> +        switch (BTF_INFO_KIND(t->info)) {
>> +        case BTF_KIND_TYPEDEF:
>> +        case BTF_KIND_VOLATILE:
>> +        case BTF_KIND_CONST:
>> +        case BTF_KIND_RESTRICT:
>> +        case BTF_KIND_TYPE_TAG:
>> +            id = t->type;
>> +            t = btf_get_type(btf, t->type);
>> +            continue;
>> +        }
>> +        break;
>> +    }
>> +
>> +    return t;
>> +}
>> +
>> +static void assign_arg(unsigned long long *arg, void *args, int size, int a)
>> +{
>> +    *arg = size == 4 ?
>> +        *(unsigned int *)(args + a * sizeof(int)) :
>> +        *(unsigned long long *)(args + a * sizeof(long long));
>> +}
>> +
>> +/**
>> + * tep_btf_print_args - Print function arguments from BTF info
>> + * @tep: The tep descriptor to use
>> + * @s: The trace_seq to write the arguments into
>> + * @args: The array that holds the arguments
>> + * @nmem: The number of arguments
>> + * @size: The size of each item in args (4 or 8).
>> + * @func: The name of the function.
>> + *
>> + * Loads up the @s with a list of arguments for the function based on
>> + * the @args.
>> + *
>> + * If there's no BTF loaded or @func is not found, then it just writes
>> + * the @args as raw numbers. Otherwise it will pretty print the
>> + * arguments based on the function info in BTF.
>> + *
>> + * Returns: 0 on success and -1 on failure.
>> + */
>> +int tep_btf_print_args(struct tep_handle *tep, struct trace_seq *s, void *args,
>> +               int nmem, int size, const char *func)
>> +{
>> +    struct tep_btf *btf = tep->btf;
>> +    struct btf_type *type = tep_btf_find_func(btf, func);
>> +    struct btf_param *param;
>> +    unsigned long long arg;
>> +    unsigned int encode;
>> +    const char *param_name;
>> +    int a, p, x, nr;
>> +
>> +    if (size != 4 && size != 8)
>> +        return -1;
>> +
>> +    if (!type) {
>> +        for (int i = 0; i < nmem; i++) {
>> +            assign_arg(&arg, args, size, i);
>> +            trace_seq_printf(s, "%llx", arg);
>> +            if (i + 1 < nmem)
>> +                trace_seq_puts(s, ", ");
>> +        }
>> +        return 0;
>> +    }
>> +
>> +    if (BTF_INFO_KIND(type->info) != BTF_KIND_FUNC) {
>> +        printf("Invalid func type %d %s\n", BTF_INFO_KIND(type->info),
>> +               btf_type_str(type));
>> +        return -1;
>> +    }
>> +
>> +    /* Get the function proto */
>> +    type = btf_get_type(btf, type->type);
>> +
>> +    /* No proto means "()" ? */
>> +    if (!type)
>> +        return 0;
>> +
>> +    if (BTF_INFO_KIND(type->info) != BTF_KIND_FUNC_PROTO) {
>> +        printf("Invalid func proto type %d %s\n", BTF_INFO_KIND(type->info),
>> +               btf_type_str(type));
>> +        return -1;
>> +    }
>> +
>> +    /* Get the number of parameters */
>> +    nr = BTF_INFO_VLEN(type->info);
>> +
>> +    /* The parameters are right after the FUNC_PROTO type */
>> +    param = ((void *)type) + sizeof(*type);
>> +
>> +    for (a = 0, p = 0; p < nr; a++, p++) {
>> +        struct btf_type *t;
>> +
>> +        if (p)
>> +            trace_seq_puts(s, ", ");
>> +
>> +        if (a == nmem) {
>> +            trace_seq_puts(s, "...");
>> +            break;
>> +        }
>> +
>> +        assign_arg(&arg, args, size, a);
>> +
>> +        param_name = btf_name(btf, param[p].name_off);
>> +        if (param_name)
>> +            trace_seq_printf(s, "%s=", param_name);
>> +
>> +        t = btf_skip_modifiers(btf, param[p].type);
>> +
>> +        switch (t ? BTF_INFO_KIND(t->info) : BTF_KIND_UNKN) {
>> +        case BTF_KIND_UNKN:
>> +            trace_seq_putc(s, '?');
>> +            /* Still print unknown type values */
>> +            /* fallthough */
>> +        case BTF_KIND_PTR:
>> +            trace_seq_printf(s, "0x%llx", arg);
>> +            break;
>> +        case BTF_KIND_INT:
>> +            encode = *(int *)((void *)t + sizeof(*t));
>> +            /* Print unsigned ints as hex */
>> +            if (BTF_INT_ENCODING(encode) & BTF_INT_SIGNED)
>> +                trace_seq_printf(s, "%lld", arg);
>> +            else
>> +                trace_seq_printf(s, "0x%llx", arg);
>> +            break;
>> +        case BTF_KIND_ENUM:
>> +            trace_seq_printf(s, "%lld", arg);
>> +            break;
>> +        default:
>> +            /* This does not handle complex arguments */
>> +            trace_seq_printf(s, "(%s)[0x%llx", btf_type_str(t), arg);
>> +            for (x = sizeof(long); x < t->size; x += sizeof(long)) {
>> +                trace_seq_putc(s, ':');
>> +                if (++a == nmem) {
>> +                    trace_seq_puts(s, "...]");
>> +                    return 0;
>> +                }
>> +                assign_arg(&arg, args, size, a);
>> +                trace_seq_printf(s, "0x%llx", arg);
>> +            }
>> +            trace_seq_putc(s, ']');
>> +            break;
>> +        }
>> +    }
>> +    return 0;
>> +}
>