[haiku-development] Re: g++ command line

  • From: Ingo Weinhold <ingo_weinhold@xxxxxx>
  • To: haiku-development@xxxxxxxxxxxxx
  • Date: Sun, 23 Feb 2014 13:44:19 +0100

On 02/22/2014 10:29 PM, Denis Papin wrote:
Because programs are linked to libroot by default, which contains the
libc and the syscall entry points.

I can then track it down to the src/system/libroot/os/team.c  that defines the 
_get_next_team_info as a call to _kern_get_next_team_info  which is defined as 
a system call in syscalls.h
I guess the "pragma syscalls begin" is where the secret lies.

But I am bumping into another mystery. Where is the _kern_get_next_team_info 
actually coded.

A file syscalls.S.inc (placed in objects/haiku/<arch>/common/system/libroot/os) is auto-generated by src/tools/gensyscalls/Jamfile from the syscalls header file headers/private/system/syscalls.h. It defines the libroot syscall functions by use of macros which expand to the architecture specific syscall invocation code.

The control flow then enters the architecture specific syscall entry point in the kernel (e.g. x86_sysenter() in src/system/kernel/arch/x86/32/interrupts.S), which in turn dispatches the syscall to the corresponding _user_*() function in the kernel. In your case that would be _user_get_next_team_info() in src/system/kernel/team.cpp.

So, leaving all the magic out, the short story is that calling a _kern_foo() syscall in libroot ends up calling a _user_foo() in the kernel. If you want to add a new syscall, just add the _kern_*() prototype to headers/private/system/syscalls.h and the implementation of a corresponding _user_*() function somewhere in the kernel.

CU, Ingo

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