3 ms·

What is up with fin? Is it really just writing an int 0 in the memory right after some variable present in libc or similar? extern fin; if(get

by mgerdts 9mo ago

What is up with fin? Is it really just writing an int 0 in the memory right after some variable present in libc or similar? extern fin; if(getpw(0, pwbuf)) goto badpw; (&fin)[1] = 0;

flatline 9mo ago
According to the chatbot, the first word of `fin` is the file descriptor, the second its state. "Reset stdin’s flags to a clean state".
oguz-ismail2 9mo ago
Predecessor of extern FILE *stdin;
formerly_proven 9mo ago
I’m guessing v4 C didn’t have structs yet (v6 C does, but struct members are actually in the global namespace and are basically just sugar for offset and a type cast; member access even worked on literals. That’s why structs from early unix APIs have prefixed member names, like st_mode.
- Boltgolt 9mo ago
  )
  - jacquesm 9mo ago
    Heh. I had the same impulse but then didn't do it, upon refreshing the page your comment was there :)
- topspin 9mo ago
  > I’m guessing v4 C didn’t have structs yet There may have been a early C without structs (B had none,) but according to Ken Thompson, the addition of structs to C was an important change, and a reason why his third attempt rewrite UNIX from assembly to a portable language finally succeeded. Certainly by the time the recently recovered v4 tape was made, C had structs: ~/unix_v4$ cat usr/sys/proc.h struct proc { char p_stat; char p_flag; char p_pri; char p_sig; char p_null; char p_time; int p_ttyp; int p_pid; int p_ppid; int p_addr; int p_size; int p_wchan; int *p_textp; } proc[NPROC]; /* stat codes */ #define SSLEEP 1 #define SWAIT 2 #define SRUN 3 #define SIDL 4 #define SZOMB 5 /* flag codes */ #define SLOAD 01 #define SSYS 02 #define SLOCK 04 #define SSWAP 010

by mgerdts 9mo ago

What is up with fin? Is it really just writing an int 0 in the memory right after some variable present in libc or similar? extern fin; if(getpw(0, pwbuf)) goto badpw; (&fin)[1] = 0;

flatline 9mo ago

According to the chatbot, the first word of `fin` is the file descriptor, the second its state. "Reset stdin’s flags to a clean state".

oguz-ismail2 9mo ago

Predecessor of extern FILE *stdin;

formerly_proven 9mo ago

I’m guessing v4 C didn’t have structs yet (v6 C does, but struct members are actually in the global namespace and are basically just sugar for offset and a type cast; member access even worked on literals. That’s why structs from early unix APIs have prefixed member names, like st_mode.

Boltgolt 9mo ago
)
- jacquesm 9mo ago
  Heh. I had the same impulse but then didn't do it, upon refreshing the page your comment was there :)
topspin 9mo ago
> I’m guessing v4 C didn’t have structs yet There may have been a early C without structs (B had none,) but according to Ken Thompson, the addition of structs to C was an important change, and a reason why his third attempt rewrite UNIX from assembly to a portable language finally succeeded. Certainly by the time the recently recovered v4 tape was made, C had structs: ~/unix_v4$ cat usr/sys/proc.h struct proc { char p_stat; char p_flag; char p_pri; char p_sig; char p_null; char p_time; int p_ttyp; int p_pid; int p_ppid; int p_addr; int p_size; int p_wchan; int *p_textp; } proc[NPROC]; /* stat codes */ #define SSLEEP 1 #define SWAIT 2 #define SRUN 3 #define SIDL 4 #define SZOMB 5 /* flag codes */ #define SLOAD 01 #define SSYS 02 #define SLOCK 04 #define SSWAP 010