mirror/libbpf
1
0
Fork 0
mirror of https://github.com/netdata/libbpf.git synced 2026-04-04 23:59:07 +08:00
Code Issues Packages Projects Releases Wiki Activity

libbpf: Support function name-based attach uprobes

Browse Source 
kprobe attach is name-based, using lookups of kallsyms to translate
a function name to an address.  Currently uprobe attach is done
via an offset value as described in [1].  Extend uprobe opts
for attach to include a function name which can then be converted
into a uprobe-friendly offset.  The calcualation is done in
several steps:

1. First, determine the symbol address using libelf; this gives us
   the offset as reported by objdump
2. If the function is a shared library function - and the binary
   provided is a shared library - no further work is required;
   the address found is the required address
3. Finally, if the function is local, subtract the base address
   associated with the object, retrieved from ELF program headers.

The resultant value is then added to the func_offset value passed
in to specify the uprobe attach address.  So specifying a func_offset
of 0 along with a function name "printf" will attach to printf entry.

The modes of operation supported are then

1. to attach to a local function in a binary; function "foo1" in
   "/usr/bin/foo"
2. to attach to a shared library function in a shared library -
   function "malloc" in libc.

[1] https://www.kernel.org/doc/html/latest/trace/uprobetracer.html

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1648654000-21758-3-git-send-email-alan.maguire@oracle.com
This commit is contained in:
Alan Maguire
2022-03-30 16:26:37 +01:00
committed by Andrii Nakryiko
parent 4a7fa5b2bc
commit d112c9ce24
2 changed files with 213 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
src/libbpf.h
View File

@@ -459,9 +459,17 @@ struct bpf_uprobe_opts {
__u64 bpf_cookie;
/* uprobe is return probe, invoked at function return time */
bool retprobe;
/* Function name to attach to. Could be an unqualified ("abc") or library-qualified
* "abc@LIBXYZ" name. To specify function entry, func_name should be set while
* func_offset argument to bpf_prog__attach_uprobe_opts() should be 0. To trace an
* offset within a function, specify func_name and use func_offset argument to specify
* offset within the function. Shared library functions must specify the shared library
* binary_path.
*/
const char *func_name;
size_t :0;
};
#define bpf_uprobe_opts__last_field retprobe
#define bpf_uprobe_opts__last_field func_name
/**
* @brief **bpf_program__attach_uprobe()** attaches a BPF program