man 2 open-read-write errors

rblampain · 06-07-2014, 06:58 AM

I guess error code like EACCES, EEXIST, EFAULT, EFBIG, EINTR and others are returned as an integer in a register in NASM, can someone tell me what numbers and what register, or point to some documentation? Preferably NASM 64 but NASM 32 will probably give an idea.

Thank you for your help.

ntubski · 06-07-2014, 08:51 AM

From http://www.x86-64.org/documentation_folder/abi.pdf (section A.2.1)

Quote:

Returning from the syscall, register %rax contains the result of the
system-call. A value in the range between -4095 and -1 indicates an error,
it is -errno.

For the actual values, see errno.h. This page has a list of them to save you having to chase down #includes.

firstfire · 06-07-2014, 09:26 AM

Hi.

The following command may be handy:

Code:

$ echo '#include <errno.h>' | cpp -dD  | less

This generates a list of #define directives for all defined macros (plus result of preprocessing):

Code:

...
#define _ASM_GENERIC_ERRNO_H 

# 1 "/usr/include/asm-generic/errno-base.h" 1 3 4

#define _ASM_GENERIC_ERRNO_BASE_H 

#define EPERM 1
#define ENOENT 2
#define ESRCH 3
#define EINTR 4
#define EIO 5
#define ENXIO 6
#define E2BIG 7
#define ENOEXEC 8
#define EBADF 9
#define ECHILD 10
#define EAGAIN 11
#define ENOMEM 12
#define EACCES 13
#define EFAULT 14
#define ENOTBLK 15
#define EBUSY 16
#define EEXIST 17
#define EXDEV 18
#define ENODEV 19
#define ENOTDIR 20
...

As a bonus, this gives a path to a header file where these constants are defined.