Packaging/Binaries: Difference between revisions

Line 280:

== Wrong file paths ==

Some programs will try to access hard-coded FHS file paths like <code>/usr/lib</code>, but mostly, this will ~~result in~~ <code>No such file</code> errors, which can break the program

Some programs will try to access hard-coded FHS file paths like <code>/usr/lib</code> or <code>/opt</code>, but mostly, this will produce silent <code>No such file</code> errors, which can break the program

To make these errors visible, we can use <code>strace</code>

<pre>

strace --trace=file,process --follow-forks --string-limit=200 \

./result/bin/some-program 2>strace.log

cat strace.log | grep -e 'No such file' -e 'execve("' \

| grep -v -E -e '(open|stat|access)(at)?\(.*"/nix/store/' \

-e resumed -e '/etc/ld-nix.so.preload'

</pre>

example:

<pre>

[pid 357679] openat(AT_FDCWD, "/opt/brother/Printers/hll3210cw/inf/lut/0600-k_cache17.bin", O_RDONLY) = -1 ENOENT (No such file or directory)

[pid 357679] openat(AT_FDCWD, "0600-k_cache17.bin", O_RDONLY) = -1 ENOENT (No such file or directory)

</pre>

this means: process 357679 is trying to open file <code>0600-k_cache17.bin</code> either from the hard-coded path in <code>/opt/brother/Printers/hll3210cw/inf/lut</code> or from the current workdir. so, as a quick fix, we could change the working directory of the wrapped binary with [https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/setup-hooks/make-wrapper.sh makeWrapper]

<pre>

makeWrapper <executable> <out_path> --run 'cd /nix/store/path/to/workdir'

</pre>

what process is throwing the <code>No such file</code> error? lets search for the process ID and the <code>exec</code> syscall

<pre>

~~strace --trace=file --follow-forks ./result/bin/some-program 2>~~strace.log

cat strace.log | grep 357679 | grep exec

~~cat strace~~.~~log | grep 'No such file' | grep~~ -~~v -e '~~/nix/store/' -~~e '~~/~~etc~~/ld-nix.so.~~preload' | grep '"~~/~~' | less -S~~

[pid 357679] execve("/nix/store/ybl1pacslmhci9zy5qv95hshdgz6ihjl-brother-hll3210cw-1.0.2-0/opt/brother/Printers/hll3210cw/lpd/brhll3210cwfilter", ["/nix/store/ybl1pacslmhci9zy5qv95"..., "-pi", "/nix/store/ybl1pacslmhci9zy5qv95"..., "-rc", "/nix/store/ybl1pacslmhci9zy5qv95"...], 0x8ba010 /* 132 vars */ <unfinished ...>

</pre>

@@ Line 280: / Line 280: @@
 == Wrong file paths ==
-Some programs will try to access hard-coded FHS file paths like <code>/usr/lib</code>, but mostly, this will result in <code>No such file</code> errors, which can break the program
+Some programs will try to access hard-coded FHS file paths like <code>/usr/lib</code> or <code>/opt</code>, but mostly, this will produce silent <code>No such file</code> errors, which can break the program
+To make these errors visible, we can use <code>strace</code>
+<pre>
+strace --trace=file,process --follow-forks --string-limit=200 \
+  ./result/bin/some-program 2>strace.log
+cat strace.log | grep -e 'No such file' -e 'execve("' \
+  | grep -v -E -e '(open|stat|access)(at)?\(.*"/nix/store/' \
+    -e resumed -e '/etc/ld-nix.so.preload'
+</pre>
+example:
+<pre>
+[pid 357679] openat(AT_FDCWD, "/opt/brother/Printers/hll3210cw/inf/lut/0600-k_cache17.bin", O_RDONLY) = -1 ENOENT (No such file or directory)
+[pid 357679] openat(AT_FDCWD, "0600-k_cache17.bin", O_RDONLY) = -1 ENOENT (No such file or directory)
+</pre>
+this means: process 357679 is trying to open file <code>0600-k_cache17.bin</code> either from the hard-coded path in <code>/opt/brother/Printers/hll3210cw/inf/lut</code> or from the current workdir. so, as a quick fix, we could change the working directory of the wrapped binary with [https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/setup-hooks/make-wrapper.sh makeWrapper]
+<pre>
+makeWrapper <executable> <out_path> --run 'cd /nix/store/path/to/workdir'
+</pre>
+what process is throwing the <code>No such file</code> error? lets search for the process ID and the <code>exec</code> syscall
 <pre>
-strace --trace=file --follow-forks ./result/bin/some-program 2>strace.log
+cat strace.log | grep 357679 | grep exec
-cat strace.log | grep 'No such file' | grep -v -e '/nix/store/' -e '/etc/ld-nix.so.preload' | grep '"/' | less -S
+[pid 357679] execve("/nix/store/ybl1pacslmhci9zy5qv95hshdgz6ihjl-brother-hll3210cw-1.0.2-0/opt/brother/Printers/hll3210cw/lpd/brhll3210cwfilter", ["/nix/store/ybl1pacslmhci9zy5qv95"..., "-pi", "/nix/store/ybl1pacslmhci9zy5qv95"..., "-rc", "/nix/store/ybl1pacslmhci9zy5qv95"...], 0x8ba010 /* 132 vars */ <unfinished ...>
 </pre>