At least in linux kernel, assuming that a.out is an elf that is linked
against relibc's own ld.so. When a user attempts `./a.out`, Linux kernel
will map `./a.out`, then map `ld.so` and jump into ld.so entry point.
In relibc ld.so will simply ignore the kernel mapped a.out and create
its own mapping. This patch forces relic ld.so to use the already mapped
`a.out` when ever possible. This would normally have slight performance
improvement (especially that currently relibc doesn't map a.out but
instead copy the data into empty mmaped memory).
The real motivation behind this patch is while impelemnting Runtime
linker debugging protocol for relibc. part of the protocol is ld.so
inseting address of some ld.so managed data structure into .dynamic
seciton of a.out then the debugger would check it there. The thing is
that debuggers have information about the kernel loaded ./a.out and they
check that one specifically which is in our case totally ignored by
relibc.
This patch keep 2 lists, one for strong symbols and one for weak
symbols. First it will check for the symbol to be resolved in the strong
symbols' list, if it is not there it will then check in the weak symbol
list.
This patch does basically two things:
- First make `global` variable not public, And make it accessable via a
function `get_sym`.
- Isolate the procedure that collect global symbols into single function
that does that and call it `collect_syms`.
The motivation of this patch is the second one where this procedure is
extended, thus it needs a seamless way to access those symbols
Introduction:
The original implementation of `relibc_ld_so_start` assumes that
ld.so will always be invoked manually as in "/lib/ld64.so ./a.out"
The problem is regarding this snippet.
if sp.argc < 2 {
eprintln!("ld.so [executable] [arguments...]");
unistd::_exit(1);
loop {}
}
As such, In linux when user types "./a.out" he will recieve the message
ld.so [executable] [arguments...]
This patch makes use of AUXV, specifically AT_ENTRY. When invoking ld.so
manually, AT_ENTRY happens to be the entry point of ld.so. But when
running `./a.out` directly, AT_ENTRY becomes the entry point of `a.out`
this patch compares AT_ENTRY to the entry point of ld.so, if they are
equal only then it will assume that argv[1] is the real program and
adjust the stack, otherwise it will proceed with the stack unadjusted.
As with the previous commit, accept() was calling inner_get_name() and
assuming only "tcp:" or "udp:" addresses would be received. Thus, in
order to support AF_UNIX sockets, inner_get_name() was split into two,
inner_af_inet() and inner_af_unix() - where the former keeps the
previous logic, dealing with "tcp:" and "udp:" addresses, and the latter
deals now with "chan:" addresses and filling in the sockaddr_un
appropriately.
Previously, domain AF_INET was assumed while processing bind() /
connect(), which end up calling bind_or_connect!. Instead, match on the
domain type and process the path for AF_UNIX domains.
To add support for UNIX sockets (AF_UNIX), of SOCK_STREAM type, the
"chan:" scheme is used, which will be supportedby the ipcd running in
userspace.
Later commits add similar AF_UNIX support for the rest of the methods in
impl PalSocket.
oddcoder