I got sidetracked hacking on truss recently. There's a lot of duplicated code
in the various ABI-specific backends, so I refactored it. I also tried to
clean up some incomplete changes from the procfs-to-trace conversion. You
can find the changes at https://reviews.freebsd.org/D3575
In particular, since I had to change the ABI-specific backends, I need testing
on other architectures besides amd64 and i386.
I've included the candidate commit message from the review below for more
Several changes to truss.
- Refactor the interface between the ABI-independent code and the
ABI-specific backends. The backends now provide smaller hooks to
fetch system call arguments and return values. The rest of the
system call entry and exit handling that was previously duplicated
among all the backends has been moved to one place.
- Merge the loop when waiting for an event with the loop for handling stops.
This also means not emulating a procfs-like interface on top of ptrace().
Instead, use a single event loop that fetches process events via waitid().
Among other things this allows us to report the full 32-bit exit value.
- Use PT_FOLLOW_FORK to follow new child processes instead of forking a new
truss process for each new child. This allows one truss process to monitor
a tree of processes and truss -c should now display one total for the
entire tree instead of separate summaries per process.
- Use the recently added fields to ptrace_lwpinfo to determine the current
system call number and argument count. The latter is especially useful
and fixes a regression since the conversion from procfs. truss now
generally prints the correct number of arguments for most system calls
rather than printing extra arguments for any call not listed in the
table in syscalls.c.
- Actually check the new ABI when processes call exec. The comments claimed
that this happened but it was not being done (perhaps this was another
regression in the conversion to ptrace()). If the new ABI after exec
is not supported, truss detaches from the process. If truss does not
support the ABI for a newly executed process the process is killed
before it returns from exec.
- Along with the refactor, teach the various ABI-specific backends to
fetch both return values, not just the first. Use this to properly
report the full 64-bit return value from lseek(). In addition, the
handler for "pipe" now pulls the pair of descriptors out of the
return values (which is the true kernel system call interface) but
displays them as an argument (which matches the interface exported by
- Each ABI handler adds entries to a linker set rather than requiring
a statically defined table of handlers in main.c.
- The arm and mips system call fetching code was changed to follow the
same pattern as amd64 (and the in-kernel handler) of fetching register
arguments first and then reading any remaining arguments from the
stack. This should fix indirect system call arguments on at least
- The mipsn32 and n64 ABIs will now look for arguments in A4 through A7.
- Use register %ebp for the 6th system call argument for Linux/i386 ABIs
to match the in-kernel argument fetch code.
- For powerpc binaries on a powerpc64 system, fetch the extra arguments
on the stack as 32-bit values that are then copied into the 64-bit
argument array instead of reading the 32-bit values directly into the