How to get meaning of flags by integer

Question

Assuming I have a syscall to open.

man 2 open gives me info, that it requires 2 or 3 parameters

int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);

So, my code runs and In my registers I have

$rdi = 0x00007fffffffdb40 → "/etc/init.d/",
$rsi = 0x0000000000000241,
$rdx = 0x00000000000001c9

How and which flags is it using during the call? How will the dir (or file) be opened?

1. I am looking at the man page. The possible flags are mentioned, but not their bit/value/integer being set by |'ing the flags together in source code.
2. I continue at the man page and see above the header files, which define the constants. In this case I'd need to #include <sys/types.h> <sys/stat.h> <fcntl.h>. However, in this files, I cannot find bits or integers, which sum or | up to the given flags ($rsi = 0x241, 577 in decimal, 1001000001 in binary) I cannot see any pattern.

Question: Do I oversee something? Do I need to look somewhere else? Where are those bits described?

Answer 1

The flags are constants drawn from here: https://github.com/torvalds/linux/blob/master/tools/include/uapi/asm-generic/fcntl.h

They can change but very rarely.

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Applying this we can see that

0x241 == O_WRONLY | O_CREAT | O_TRUNC