On Wed, Apr 26, 2023 at 02:47:27PM -0700, Yonghong Song wrote:
On 4/23/23 11:55 AM, Espen Grindhaug wrote:
This change fixes the handling of versions in elf_find_func_offset. In the previous implementation, we incorrectly assumed that the
Could you give more explanation/example in the commit message what does 'incorrectly' mean here? In which situations the current libbpf implementation will not be correct?
How about something like this?
libbpf: Improve version handling when attaching uprobe
This change fixes the handling of versions in elf_find_func_offset.
For example, let's assume we are trying to attach an uprobe to pthread_create in glibc. Prior to this commit, it would fail with an error message saying 'elf: ambiguous match [...]', this is because there are two entries in the symbol table with that name.
$ nm -D /lib/x86_64-linux-gnu/libc.so.6 | grep pthread_create 0000000000094cc0 T pthread_create@GLIBC_2.2.5 0000000000094cc0 T pthread_create@@GLIBC_2.34
So we go ahead and modify our code to attach to 'pthread_create@@GLIBC_2.34', and this also fails, but this time with the error 'elf: failed to find symbol [...]'. This fails because we incorrectly assumed that the version information would be present in the string found in the string table, but there is only the string 'pthread_create'.
This patch reworks how we compare the symbol name provided by the user if it is qualified with a version (using @ or @@). We now look up the correct version string in the version symbol table before constructing the full name, as also done above by nm, before comparing.
version information would be present in the string found in the string table.
We now look up the correct version string in the version symbol table before constructing the full name and then comparing.
This patch adds support for both name@version and name@@version to match output of the various elf parsers.
Signed-off-by: Espen Grindhaug espen.grindhaug@gmail.com
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