3 ms·

Zig certainly needs more work. That part is more on familiarity with Zig and how intuitive it is or isn't. In any case I would recommend anyone investigating t

by hawski 3y ago

Zig certainly needs more work. That part is more on familiarity with Zig and how intuitive it is or isn't. In any case I would recommend anyone investigating things like that to run things through strace. It is often my first step in trying to understand what happens with anything - like a cryptic error "No such file or directory" without telling me what a thing tried to access. You would run: $ strace -f sh -c 'your | pipeline | here' -o strace.log You could then track things easily and see what is really happening. Cheers!

mtlynch 3y ago
Thanks for the tip! I don't have experience with strace, and I'm wondering if I'm misunderstanding what you're saying. I tried running your suggested command, and I got 2,800 lines of output like this: execve("/nix/store/vqvj60h076bhqj6977caz0pfxs6543nb-bash-5.2-p15/bin/sh", ["sh", "-c", "echo \"60016000526001601ff3\" | xx"...], 0x7fffffffcf38 /* 106 vars */) = 0 brk(NULL) = 0x4ea000 arch_prctl(0x3001 /* ARCH_??? */, 0x7fffffffcdd0) = -1 EINVAL (Invalid argument) access("/etc/ld-nix.so.preload", R_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/nix/store/aw2fw9ag10wr9pf0qk4nk5sxi0q0bn56-glibc-2.37-8/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832 newfstatat(3, "", {st_mode=S_IFREG|0555, st_size=15688, ...}, AT_EMPTY_PATH) = 0 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ffff7fc2000 mmap(NULL, 16400, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7ffff7fbd000 mmap(0x7ffff7fbe000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1000) = 0x7ffff7fbe000 Am I doing it wrong? Or is there more training involved before one could usefully integrate this into debugging? Because to me, the output is pretty inscrutable.
- hawski 3y ago
  There is a lot of output here, but you can grep around or filter with strace CLI. If you used -f option you should get PID numbers later on. Then you can look for all execve's to see how PIDs map to parts of the pipeline. For now maybe grep the log file with something like: "grep -e clone -e execve -e write -e read". You can do this with strace CLI, but I never remember the syntax and usually analyze the log extensively. I think something like this could work: strace -f -e execve,clone,write,read -o strace.log sh -c '...' Clone is fork, so a creation of a new process, before eventual execve (with echo there will probably be just clone).
- dgoldstein0 3y ago
  strace tells you every syscall the process under it makes. So very helpful to understanding how a program interacts with the operating system - and I/O as all IO mechanisms are managed by the operating system. As for how to filter this I'll leave that to the other comments, but I personally would look at the man page or Google around for tips

by hawski 3y ago

mtlynch 3y ago

Thanks for the tip! I don't have experience with strace, and I'm wondering if I'm misunderstanding what you're saying. I tried running your suggested command, and I got 2,800 lines of output like this: execve("/nix/store/vqvj60h076bhqj6977caz0pfxs6543nb-bash-5.2-p15/bin/sh", ["sh", "-c", "echo \"60016000526001601ff3\" | xx"...], 0x7fffffffcf38 /* 106 vars */) = 0 brk(NULL) = 0x4ea000 arch_prctl(0x3001 /* ARCH_??? */, 0x7fffffffcdd0) = -1 EINVAL (Invalid argument) access("/etc/ld-nix.so.preload", R_OK) = -1 ENOENT (No such file or directory) openat(AT_FDCWD, "/nix/store/aw2fw9ag10wr9pf0qk4nk5sxi0q0bn56-glibc-2.37-8/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832 newfstatat(3, "", {st_mode=S_IFREG|0555, st_size=15688, ...}, AT_EMPTY_PATH) = 0 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ffff7fc2000 mmap(NULL, 16400, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7ffff7fbd000 mmap(0x7ffff7fbe000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1000) = 0x7ffff7fbe000 Am I doing it wrong? Or is there more training involved before one could usefully integrate this into debugging? Because to me, the output is pretty inscrutable.

hawski 3y ago
There is a lot of output here, but you can grep around or filter with strace CLI. If you used -f option you should get PID numbers later on. Then you can look for all execve's to see how PIDs map to parts of the pipeline. For now maybe grep the log file with something like: "grep -e clone -e execve -e write -e read". You can do this with strace CLI, but I never remember the syntax and usually analyze the log extensively. I think something like this could work: strace -f -e execve,clone,write,read -o strace.log sh -c '...' Clone is fork, so a creation of a new process, before eventual execve (with echo there will probably be just clone).
dgoldstein0 3y ago
strace tells you every syscall the process under it makes. So very helpful to understanding how a program interacts with the operating system - and I/O as all IO mechanisms are managed by the operating system. As for how to filter this I'll leave that to the other comments, but I personally would look at the man page or Google around for tips