Bad error message when missing compiler

[gbruer15]

devito/devito/arch/compiler.py

Lines 38 to 50 in fe47e96

	try:
	res = run([cc, "--version"], stdout=PIPE, stderr=DEVNULL)
	ver = res.stdout.decode("utf-8")
	if not ver:
	return Version("0")
	except UnicodeDecodeError:
	return Version("0")
	except FileNotFoundError:
	if allow_fail:
	return Version("0")
	else:
	error("The `%s` compiler isn't available on this system" % cc)
	sys.exit(1)

The reason for catching the FileNotFoundError is likely to print out a nice error message if the compiler command can't be found. But the actual error that is thrown when someone tries to run a nonexistent executable is a permissions error, which is not being caught.

The documentation for subprocess indicates OSError will be thrown in case of missing program. (Search "OSError" on https://docs.python.org/3/library/subprocess.html)

If this makes sense, I can make a pull request to fix it next week.

[mloubout]

Will have a look, thanks. Haven't touch this part in a while so probably right, PR always welcome!

Out of curiosity, what setting triggered this? We never encountered that case.

[gbruer15]

I was trying to run on a GPU in a conda environment with Python 3.12.1. I think my issue is I don't have a package for nvc++ installed.

Here's environment variables:

export DEVITO_LANGUAGE=openacc
export DEVITO_ARCH=nvc
export DEVITO_PLATFORM=nvidiaX

export OMP_NUM_TREADS=1
export JULIA_NUM_THREADS=1

Here's the error message that I get when trying to import my Julia package that uses JUDI that uses Devito:

julia> using SeismicPlumeEnsembleFilter
ERROR: InitError: PyError (PyImport_ImportModule) <class 'PermissionError'>
PermissionError(13, 'Permission denied')
  File "/storage/home/hcoda1/4/gbruer3/.julia/packages/JUDI/9qfzJ/src/pysource/models.py", line 4, in <module>
    from devito import (Grid, Function, SubDomain, SubDimension, Eq, Inc,
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/__init__.py", line 123, in <module>
    init_configuration()
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/parameters.py", line 229, in init_configuration
    configuration.initialize()
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/parameters.py", line 137, in initialize
    self[k] = v
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/parameters.py", line 62, in wrapper
    return func(self, key, value)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/parameters.py", line 53, in wrapper
    return func(self, key, value)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/parameters.py", line 93, in __setitem__
    self._updated(key, value)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/parameters.py", line 80, in _updated
    retval = self._update_functions[key](value)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/__init__.py", line 53, in <lambda>
    callback=lambda i: compiler_registry[i]())
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/arch/compiler.py", line 534, in __init__
    super(PGICompiler, self).__init__(*args, cpp=True, **kwargs)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/arch/compiler.py", line 203, in __init__
    self.version = sniff_compiler_version(self.CC)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/tools/memoization.py", line 34, in __call__
    value = self.func(*args, **kw)
  File "/storage/home/hcoda1/4/gbruer3/.local/lib/python3.9/site-packages/devito/arch/compiler.py", line 36, in sniff_compiler_version
    res = run([cc, "--version"], stdout=PIPE, stderr=DEVNULL)
  File "/usr/local/pace-apps/spack/packages/linux-rhel7-x86_64/gcc-4.8.5/python-3.9.12-rkxvr6vh25rasj7rrhxd3hpaasuqwcoy/lib/python3.9/subprocess.py", line 505, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/local/pace-apps/spack/packages/linux-rhel7-x86_64/gcc-4.8.5/python-3.9.12-rkxvr6vh25rasj7rrhxd3hpaasuqwcoy/lib/python3.9/subprocess.py", line 951, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/local/pace-apps/spack/packages/linux-rhel7-x86_64/gcc-4.8.5/python-3.9.12-rkxvr6vh25rasj7rrhxd3hpaasuqwcoy/lib/python3.9/subprocess.py", line 1821, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)

Stacktrace:
  [1] pyimport(name::String)
    @ PyCall ~/.julia/packages/PyCall/1gn3u/src/PyCall.jl:558
  [2] __init__()
    @ JUDI ~/.julia/packages/JUDI/9qfzJ/src/JUDI.jl:169
  [3] _include_from_serialized(pkg::Base.PkgId, path::String, depmods::Vector{Any})
    @ Base ./loading.jl:831
  [4] _tryrequire_from_serialized(modkey::Base.PkgId, path::String, sourcepath::String, depmods::Vector{Any})
    @ Base ./loading.jl:938
  [5] _require_search_from_serialized(pkg::Base.PkgId, sourcepath::String, build_id::UInt64)
    @ Base ./loading.jl:1028
  [6] _require(pkg::Base.PkgId)
    @ Base ./loading.jl:1315
  [7] _require_prelocked(uuidkey::Base.PkgId)
    @ Base ./loading.jl:1200
  [8] macro expansion
    @ ./loading.jl:1180 [inlined]
  [9] macro expansion
    @ ./lock.jl:223 [inlined]
 [10] require(into::Module, mod::Symbol)
    @ Base ./loading.jl:1144
during initialization of module JUDI

[gbruer15]

In Python, it at least prints out why command is giving the PermissionError, so it seems like some information is lost when the exception goes through Julia.

>>> import devito
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/__init__.py", line 136, in <module>
    init_configuration()
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/parameters.py", line 222, in init_configuration
    configuration.initialize()
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/parameters.py", line 130, in initialize
    self[k] = v
    ~~~~^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/parameters.py", line 62, in wrapper
    return func(self, key, value)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/parameters.py", line 53, in wrapper
    return func(self, key, value)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/parameters.py", line 84, in __setitem__
    value = self._update_functions[key](value)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/__init__.py", line 63, in <lambda>
    callback=lambda i: compiler_registry[i]())
                       ^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/arch/compiler.py", line 576, in __init__
    super().__init__(*args, cpp=True, **kwargs)
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/arch/compiler.py", line 217, in __init__
    self.version = sniff_compiler_version(self.CC)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/tools/memoization.py", line 34, in __call__
    value = self.func(*args, **kw)
            ^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/site-packages/devito/arch/compiler.py", line 37, in sniff_compiler_version
    res = run([cc, "--version"], stdout=PIPE, stderr=DEVNULL)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/subprocess.py", line 548, in run
    with Popen(*popenargs, **kwargs) as process:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/subprocess.py", line 1026, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/storage/coda1/p-echow7/0/gbruer3/julia/JutulJUDIFilter/SeismicPlumeExperiments/conda-env/lib/python3.12/subprocess.py", line 1953, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
PermissionError: [Errno 13] Permission denied: 'nvc++'

[mloubout]

This is quite curious, never seen that before almost looks like it finds nvc++ in some weird path you don't have access to.

More than happy to get the PR to make it more robust.

[gbruer15]

Here's more info about how this happens.

The permissions error won't happen if the user has access to every folder. It seems there's some folder in the PATH variable that I don't have access to. When exec or something similar checks each folder in PATH, it encounters an unaccessible location, and that's the error it ends up returning.

https://www.linuxquestions.org/questions/programming-9/execvp-function-behaviour-for-root-vs-user-4175599625/#post5669769

Here's a simple program to show the behavior:

#include <stdio.h>
#include <unistd.h>
#include <errno.h>

int main(int argc, const char** argv) {
    int rv;
    char * const* args = {NULL};
    rv = execvp("./doesntexist", args);
    if (rv == -1) {
        perror("");
    }
    rv = execvp("doesntexist", args);
    if (rv == -1) {
        perror("");
    }
    return 0;
}

Output:

No such file or directory
Permission denied