Hi, As suggested by https://www.kernel.org/doc/man-pages/reporting_bugs.html , I looked up the online man page as well: http://man7.org/linux/man-pages/man2/syscall.2.html In the table in "Architecture calling conventions" section: arch/ABI instruction syscall # retval error Notes ──────────────────────────────────── x86-64 syscall rax rax - [5] Retval must be placed in rdi as per the following link: https://w3challs.com/syscalls/?arch=x86_64 I ran the test to verify that the retval is indeed supposed to be placed in rdi, and not rax as the man page incorrectly suggests. My man page version: $ man --version man 2.8.3 Steps to replicate this issue: Step 1) Write test code 'startup.c': void _start() { /* Source: $: man syscall arch/ABI instruction syscall # retval error Notes ──────────────────────────────────────────────────────────────────── i386 int $0x80 eax eax - ia64 break 0x100000 r15 r8 r10 [1] x86-64 syscall rax rax - [5] */ // Specify the return value/error code in ebx for x86 and rdi for x86_64 asm volatile ( "movq $97, %rdi" ); // Specify the type of system call (1 is the exit syscall) in eax register. asm volatile ( "movq $0x3c, %rax" ); // Transition to kernel mode. asm volatile ( "syscall" ); } Step 2) Compile and execute: $ gcc -nostdlib -c startup.c $ ld startup.o -o startup $ ./startup $ echo $? 97 My system details: $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.1 LTS Release: 18.04 Codename: bionic $ uname -a Linux user 4.15.0-51-generic #55-Ubuntu SMP Wed May 15 14:27:21 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux Please let me know if there's anything else you need to rectify this issue. Thanks Naveen On Sun, Jun 23, 2019 at 8:57 AM Naveen Iyer <iyernaveenr@xxxxxxxxx> wrote: > > Hi, > > As sugegsted by https://www.kernel.org/doc/man-pages/reporting_bugs.html , I looked up the online man page as well: > http://man7.org/linux/man-pages/man2/syscall.2.html > > In the table in "Architecture calling conventions" section: > > arch/ABI instruction syscall # retval error Notes > ──────────────────────────────────────────────────────────────────── > x86-64 syscall rax rax - [5] > > Retval must be placed in rdi as per the following link: > https://w3challs.com/syscalls/?arch=x86_64 > > I personally ran the test to verify that the retval is indeed supposed to be placed in rdi, not rax. > My man page version: > $ man --version > man 2.8.3 > > Steps to replicate this issue: > Step 1) > Write test code 'startup.c': > void _start() > { > /* > Source: $: man syscall > arch/ABI instruction syscall # retval error Notes > ──────────────────────────────────────────────────────────────────── > i386 int $0x80 eax eax - > ia64 break 0x100000 r15 r8 r10 [1] > x86-64 syscall rax rax - [5] > */ > > // Specify the return value/error code in ebx for x86 and rdi for x86_64 > asm volatile ( > "movq $97, %rdi" > ); > > // Specify the type of system call (1 is the exit syscall) in eax register. > asm volatile ( > "movq $0x3c, %rax" > ); > > // Transition to kernel mode. > asm volatile ( > "syscall" > ); > } > > Step 2) Compile and execute: > $ gcc -nostdlib -c startup.c > $ ld startup.o -o startup > $ ./startup > $ echo $? > 97 > > My system details: > $ lsb_release -a > No LSB modules are available. > Distributor ID: Ubuntu > Description: Ubuntu 18.04.1 LTS > Release: 18.04 > Codename: bionic > > $ uname -a > Linux user 4.15.0-51-generic #55-Ubuntu SMP Wed May 15 14:27:21 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux > > Please let me know if there's anything else you need to rectify this issue. > > Thanks > Naveen
