usertools/pmdinfo: remove dependency to ldd
Checks
Commit Message
Some environments (buildroot) do not have the ldd utility installed by
default. However, ldd is often only a wrapper shell script that actually
checks that the arguments are valid ELF files and executes them with
the LD_TRACE_LOADED_OBJECTS=1 variable set in the environment.
Since ld.so is the actual ELF interpreter which is loaded first when
executing a program, executing any dynamic ELF program/library with that
variable set will cause all dependent dynamic libraries to be printed
and ld.so will exit before even running main.
Excerpt from ld.so(7) man page:
LD_TRACE_LOADED_OBJECTS
If set (to any value), causes the program to list its dynamic
dependencies, as if run by ldd(1), instead of running normally.
Change dpdk-pmdinfo.py to actually "execute" the files provided on the
command line with LD_TRACE_LOADED_OBJECTS=1 set. Ensure that the files
are valid dynamically executable ELF programs to avoid obscure and
confusing errors.
Reported-by: Olivier Matz <olivier.matz@6wind.com>
Signed-off-by: Robin Jarry <rjarry@redhat.com>
---
doc/guides/tools/pmdinfo.rst | 4 ++--
usertools/dpdk-pmdinfo.py | 34 +++++++++++++++++++++++-----------
2 files changed, 25 insertions(+), 13 deletions(-)
Comments
Hi Robin,
On Thu, Oct 13, 2022 at 03:41:25PM +0200, Robin Jarry wrote:
> Some environments (buildroot) do not have the ldd utility installed by
> default. However, ldd is often only a wrapper shell script that actually
> checks that the arguments are valid ELF files and executes them with
> the LD_TRACE_LOADED_OBJECTS=1 variable set in the environment.
>
> Since ld.so is the actual ELF interpreter which is loaded first when
> executing a program, executing any dynamic ELF program/library with that
> variable set will cause all dependent dynamic libraries to be printed
> and ld.so will exit before even running main.
>
> Excerpt from ld.so(7) man page:
>
> LD_TRACE_LOADED_OBJECTS
> If set (to any value), causes the program to list its dynamic
> dependencies, as if run by ldd(1), instead of running normally.
>
> Change dpdk-pmdinfo.py to actually "execute" the files provided on the
> command line with LD_TRACE_LOADED_OBJECTS=1 set. Ensure that the files
> are valid dynamically executable ELF programs to avoid obscure and
> confusing errors.
>
> Reported-by: Olivier Matz <olivier.matz@6wind.com>
> Signed-off-by: Robin Jarry <rjarry@redhat.com>
Tested on buildroot without ldd.
Reviewed-by: Olivier Matz <olivier.matz@6wind.com>
On Fri, Oct 14, 2022 at 04:02:02PM +0200, Olivier Matz wrote:
> Hi Robin,
>
> On Thu, Oct 13, 2022 at 03:41:25PM +0200, Robin Jarry wrote:
> > Some environments (buildroot) do not have the ldd utility installed by
> > default. However, ldd is often only a wrapper shell script that actually
> > checks that the arguments are valid ELF files and executes them with
> > the LD_TRACE_LOADED_OBJECTS=1 variable set in the environment.
> >
> > Since ld.so is the actual ELF interpreter which is loaded first when
> > executing a program, executing any dynamic ELF program/library with that
> > variable set will cause all dependent dynamic libraries to be printed
> > and ld.so will exit before even running main.
> >
> > Excerpt from ld.so(7) man page:
> >
> > LD_TRACE_LOADED_OBJECTS
> > If set (to any value), causes the program to list its dynamic
> > dependencies, as if run by ldd(1), instead of running normally.
> >
> > Change dpdk-pmdinfo.py to actually "execute" the files provided on the
> > command line with LD_TRACE_LOADED_OBJECTS=1 set. Ensure that the files
> > are valid dynamically executable ELF programs to avoid obscure and
> > confusing errors.
> >
> > Reported-by: Olivier Matz <olivier.matz@6wind.com>
> > Signed-off-by: Robin Jarry <rjarry@redhat.com>
>
> Tested on buildroot without ldd.
>
> Reviewed-by: Olivier Matz <olivier.matz@6wind.com>
After some more tests, it appears that it only works for an executable
binary, but it does not work for .so PMDs:
# LD_TRACE_LOADED_OBJECTS=1 /usr/lib/x86_64-linux-gnu/dpdk/pmds-22.0/librte_net_ixgbe.so
Segmentation fault (core dumped)
So it is maybe better to keep the original code using ldd.
Thank you Robin anyway.
@@ -37,8 +37,8 @@ Arguments
.. option:: ELF_FILE
- DPDK application binary or dynamic library.
- Any linked ``librte_*.so`` library (as reported by ``ldd``) will also be analyzed.
+ Executable DPDK application binary or dynamic library.
+ Any linked ``librte_*.so`` library (as reported by ``ld.so``) will also be analyzed.
Can be specified multiple times.
Environment Variables
@@ -97,9 +97,9 @@ def parse_args() -> argparse.Namespace:
"elf_files",
metavar="ELF_FILE",
nargs="+",
- type=existing_file,
+ type=executable_elf_file,
help="""
- DPDK application binary or dynamic library.
+ Executable DPDK application binary or dynamic library.
""",
)
return parser.parse_args()
@@ -180,14 +180,24 @@ def get_plugin_libs(binaries: Iterable[Path]) -> Iterator[Path]:
# ----------------------------------------------------------------------------
-def existing_file(value: str) -> Path:
+def executable_elf_file(value: str) -> Path:
"""
- Argparse type= callback to ensure an argument points to a valid file path.
+ Argparse type= callback to ensure an argument points to a valid ELF file
+ path which can be executed.
"""
- path = Path(value)
- if not path.is_file():
- raise argparse.ArgumentTypeError(f"{value}: No such file")
- return path
+ try:
+ with open(value, "rb") as f:
+ elf = ELFFile(f)
+ if elf.header.e_type not in ("ET_DYN", "ET_EXEC"):
+ raise ELFError(f"unknown type: {elf.header.e_type!r}")
+ if not os.access(value, os.X_OK):
+ raise OSError("is not executable")
+ except ELFError as e:
+ raise argparse.ArgumentTypeError(f"{value}: invalid ELF: {e}") from e
+ except OSError as e:
+ raise argparse.ArgumentTypeError(f"{value}: {e}") from e
+
+ return Path(value)
# ----------------------------------------------------------------------------
@@ -270,7 +280,7 @@ def get_elf_strings(path: Path, section: str, prefix: str) -> Iterator[str]:
# ----------------------------------------------------------------------------
-LDD_LIB_RE = re.compile(
+LOADED_OBJECT_RE = re.compile(
r"""
^ # beginning of line
\t # tab
@@ -290,14 +300,16 @@ def get_needed_libs(path: Path) -> Iterator[Path]:
"""
Extract the dynamic library dependencies from an ELF executable.
"""
+ env = os.environ.copy()
+ env["LD_TRACE_LOADED_OBJECTS"] = "1"
with subprocess.Popen(
- ["ldd", str(path)], stdout=subprocess.PIPE, stderr=subprocess.PIPE
+ [str(path)], stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=env
) as proc:
out, err = proc.communicate()
if proc.returncode != 0:
err = err.decode("utf-8").splitlines()[-1].strip()
raise Exception(f"cannot read ELF file: {err}")
- for match in LDD_LIB_RE.finditer(out.decode("utf-8")):
+ for match in LOADED_OBJECT_RE.finditer(out.decode("utf-8")):
libname, libpath = match.groups()
if libname.startswith("librte_"):
libpath = Path(libpath)