Re: [PATCH v2 2/2] selftests/ftrace: Convert ELF entry point to file offset in uprobe test

On Fri,  7 Aug 2026 16:15:12 +0800
"Rui Qi" <[email protected]> wrote:

> The add_remove_uprobe test uses readelf -h to obtain the ELF entry
> point (e_entry) and passes it directly as the offset to uprobe_events.
> However, uprobe_events expects a file offset, not a virtual address.
> 
> For PIE binaries, the virtual address happens to equal the file offset
> because the first LOAD segment has p_vaddr == p_offset, so the test
> works by coincidence. But for non-PIE executables, e_entry is an
> absolute virtual address that can far exceed the file size. When the
> probe is enabled, uprobe_register() checks offset > i_size_read(inode)
> and rejects it with -EINVAL.

Good catch!

> 
> Fix this by converting the virtual address to a file offset using the
> ELF program headers: scan readelf -lW output for the LOAD segment
> containing the entry point, then compute file_offset = e_entry -
> p_vaddr + p_offset. For PIE binaries the result is unchanged; for
> non-PIE binaries the offset is correctly translated.
> 
> The conversion uses only POSIX shell primitives, with no dependency on
> gawk or perl.
> 
> Fixes: dc4b165855f2 ("selftests/ftrace: Use readelf to find entry point in uprobe test")
> Signed-off-by: Rui Qi <[email protected]>

OK, let me take it.

Thank you!

> ---
>  .../test.d/dynevent/add_remove_uprobe.tc      | 27 +++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
> index f2048c244526..19430bd5864c 100644
> --- a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
> +++ b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
> @@ -12,9 +12,32 @@ echo 0 > events/enable
>  echo > dynamic_events
>  
>  REALBIN=`readlink -f /bin/sh`
> -ENTRYPOINT=`readelf -h ${REALBIN} | grep Entry | sed -e 's/[^0]*//'`
>  
> -echo "p:myevent ${REALBIN}:${ENTRYPOINT}" >> uprobe_events
> +# Get the entry point virtual address from ELF header
> +ENTRY=`readelf -hW ${REALBIN} | grep "Entry point" | awk '{print $NF}'`
> +
> +# Convert virtual address to file offset: find the LOAD segment containing
> +# the entry point, then compute file_offset = e_entry - p_vaddr + p_offset.
> +# For PIE binaries this is a no-op (vaddr == file offset), but for non-PIE
> +# executables the virtual address is much larger than the file size and
> +# must be converted, otherwise uprobe_register() rejects it with -EINVAL.
> +ENTRY_DEC=$(printf '%d' "$ENTRY")
> +OFFSET=$ENTRY
> +while IFS= read -r line; do
> +    set -- $line
> +    [ "$1" = "LOAD" ] || continue
> +    VA_DEC=$(printf '%d' "$3")
> +    OFF_DEC=$(printf '%d' "$2")
> +    FSZ_DEC=$(printf '%d' "$5")
> +    if [ "$ENTRY_DEC" -ge "$VA_DEC" ] && [ "$ENTRY_DEC" -lt "$((VA_DEC + FSZ_DEC))" ]; then
> +        OFFSET=$(printf '0x%x' "$((ENTRY_DEC - VA_DEC + OFF_DEC))")
> +        break
> +    fi
> +done << EOF
> +$(readelf -lW ${REALBIN} | grep LOAD)
> +EOF
> +
> +echo "p:myevent ${REALBIN}:${OFFSET}" >> uprobe_events
>  
>  grep -q myevent uprobe_events
>  test -d events/uprobes/myevent
> -- 
> 2.20.1


-- 
Masami Hiramatsu (Google) <[email protected]>