ptrace #129

arihant2math · 2026-01-05T23:07:50Z

No description provided.

Fix current task double-borrow bug when exiting with a signal.

Make it such that when a ptrace event is hit: - The current regset is saved in the ptrace state. - The current task is put to sleep. - Arrange for a SIGCHLD to be set to the parent. - Notify any waiters with the appopriate signal.

handle `PTRACE_CONT` and `PTRACE_SYSCALL` operations.

Add option definitions `PTRACE_O_*` and change the ptrace state depdening upon which options are set in the call.

When a new child stops due to a stoppable-signal after PTRACE_TRACEME, send a SIGSTOP with a `PTRACE_EVENT_STOP`.

Add a function that allows an owned page to be atomically obtained from a new process.

We currently union the UNMASKABLE_SIGNALS set with the new signal mask. This does the complete opposite of what we wnat, we want to *remove* those signals from the newly computed signal mask. This patch removes the UNMASKABLE_SIGNALS set from any newly computed signal mask.

Implement the `sys_process_vm_readv` syscall.

If a SIGKILL has been received, ensure all sleepy tasks are set to runnable so that they can action the signal.

If a task has called one of `sys_exit` or `sys_exit_group`, don't follow the standard syscall exit path. Since the task is dead and it will never be rescheduled, there's no point in processing the result of sys_exit.

Add ptrace events for the exit family of syscalls.

If the calling process has no children and no pending exit events to handle, return ECHILD instead of waiting forever.

hexagonal-sun · 2026-01-11T22:37:18Z

@arihant2math Okay, this now implements of enough ptrace logic to make strace work in moss! This also required the ability to get pages from another address space into the tracer for syscall arg decoding. I added the get_pages() function to do that and it's main userspace interface is implemented with sys_process_vm_readv.

I've also attached an strace binary to this comment so people have have a play.

strace.gz

[root@moss-machine /]# ./strace /bin/ls
./strace /bin/ls
execve("/bin/ls", ["/bin/ls"], 0x7fffffffff40 /* 3 vars */) = 0
brk(NULL)                               = 0x800000000000
faccessat(AT_FDCWD, "/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=20859, ...}) = 0
mmap(NULL, 20859, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fffff7fa000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/libcap.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0\267\0\1\0\0\0`}\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=67584, ...}) = 0
mmap(NULL, 196704, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_DENYWRITE, -1, 0) = 0x7fffff7c9000
mmap(0x7fffff7d0000, 131168, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0) = 0x7fffff7d0000
munmap(0x7fffff7c9000, 28672)           = 0
munmap(0x7fffff7f1000, 32864)           = 0
mprotect(0x7fffff7da000, 86016, PROT_NONE) = 0
mmap(0x7fffff7ef000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xf000) = 0x7fffff7ef000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0\267\0\1\0\0\0\340%\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1853856, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fffff7f8000
mmap(NULL, 1936736, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_DENYWRITE, -1, 0) = 0x7fffff5f7000
mmap(0x7fffff600000, 1871200, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0) = 0x7fffff600000
munmap(0x7fffff5f7000, 36864)           = 0
munmap(0x7fffff7c9000, 28000)           = 0
mprotect(0x7fffff7b0000, 53248, PROT_NONE) = 0
mmap(0x7fffff7bd000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bd000) = 0x7fffff7bd000
mmap(0x7fffff7c2000, 28000, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fffff7c2000
close(3)                                = 0
set_tid_address(0x7fffff7f8f50)         = 4
set_robust_list(0x7fffff7f8f60, 24)     = 0
rseq(0x7fffff7f9640, 0x20, 0, 0xd428bc00) = -1 ENOSYS (Function not implemented)
mprotect(0x7fffff7bd000, 12288, PROT_READ) = 0
mprotect(0x7fffff7ef000, 4096, PROT_READ) = 0
mprotect(0x50000003e000, 8192, PROT_READ) = 0
mprotect(0x70000003e000, 8192, PROT_READ) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
getrandom("\x15\x5d\x7f\xdf\x82\x27\xf7\x30", 8, GRND_NONBLOCK) = 8
munmap(0x7fffff7fa000, 20859)           = 0
prctl(PR_CAPBSET_READ, CAP_MAC_OVERRIDE) = 1
prctl(PR_CAPBSET_READ, 0x30 /* CAP_??? */) = -1 EINVAL (Invalid argument)
prctl(PR_CAPBSET_READ, CAP_CHECKPOINT_RESTORE) = 1
prctl(PR_CAPBSET_READ, 0x2c /* CAP_??? */) = -1 EINVAL (Invalid argument)
prctl(PR_CAPBSET_READ, 0x2a /* CAP_??? */) = -1 EINVAL (Invalid argument)
prctl(PR_CAPBSET_READ, 0x29 /* CAP_??? */) = -1 EINVAL (Invalid argument)
brk(NULL)                               = 0x800000000000
brk(0x800000021000)                     = 0x800000021000
ioctl(1, TCGETS2, 0x7ffffffffc48)       = -1 ENOTTY (Inappropriate ioctl for device)
openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
fstat(3, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
getdents64(3, 0x800000005000 /* 26 entries */, 32768) = 672
getdents64(3, 0x800000005000 /* 0 entries */, 32768) = 0
close(3)                                = 0
fstat(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(0, 0), ...}) = 0
ioctl(1, TCGETS2, 0x7fffffffd678)       = -1 ENOTTY (Inappropriate ioctl for device)
write(1, "a.out\nbash\nbin\nboot\nbusybox\ndev\n"..., 126a.out
bash
bin
boot
busybox
dev
etc
home
lib
lost+found
mnt
opt
proc
root
run
sbin
srv
strace
sys
test.c
tmp
usertest
usr
var
) = 126
close(1)                                = 0
close(2)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++
[root@moss-machine /]#

arihant2math

LGTM!

arihant2math force-pushed the ptrace branch 4 times, most recently from 9412aa5 to 51e39b3 Compare January 5, 2026 23:54

arihant2math and others added 8 commits January 9, 2026 11:34

initial ptrace

82b6649

uspc_ret: ensure task is dropped before exiting

bd1b661

Fix current task double-borrow bug when exiting with a signal.

ptrace: add event waiting

ea6b2c7

Make it such that when a ptrace event is hit: - The current regset is saved in the ptrace state. - The current task is put to sleep. - Arrange for a SIGCHLD to be set to the parent. - Notify any waiters with the appopriate signal.

ptrace: handle continuiation calls

c23ee87

handle `PTRACE_CONT` and `PTRACE_SYSCALL` operations.

ptrace: implement PTRACE_SETOPTIONS

3332f04

Add option definitions `PTRACE_O_*` and change the ptrace state depdening upon which options are set in the call.

ptrace: send SIGSTOP and PTRACE_EVENT_STOP for stoppable signal

1d5fa89

When a new child stops due to a stoppable-signal after PTRACE_TRACEME, send a SIGSTOP with a `PTRACE_EVENT_STOP`.

process: get_page: new

d7ea4f5

Add a function that allows an owned page to be atomically obtained from a new process.

hexagonal-sun force-pushed the ptrace branch from 51e39b3 to cf7c700 Compare January 11, 2026 22:26

hexagonal-sun added 5 commits January 11, 2026 22:29

syscalls: sys_process_vm_readv: implement

f99bbd0

Implement the `sys_process_vm_readv` syscall.

kill: awake sleepy tasks on SIGKILL

ede3dbe

If a SIGKILL has been received, ensure all sleepy tasks are set to runnable so that they can action the signal.

arch: arm64: syscall: don't return result on task exit

33f8f3a

If a task has called one of `sys_exit` or `sys_exit_group`, don't follow the standard syscall exit path. Since the task is dead and it will never be rescheduled, there's no point in processing the result of sys_exit.

syscall: sys_exit*: add ptrace events

fb8ff29

Add ptrace events for the exit family of syscalls.

process: sys_wait4: return ECHILD with no children

00071a7

If the calling process has no children and no pending exit events to handle, return ECHILD instead of waiting forever.

hexagonal-sun force-pushed the ptrace branch from cf7c700 to 00071a7 Compare January 11, 2026 22:30

hexagonal-sun marked this pull request as ready for review January 11, 2026 22:31

arihant2math commented Jan 12, 2026

View reviewed changes

arihant2math merged commit 64bc004 into hexagonal-sun:master Jan 12, 2026
4 checks passed

arihant2math deleted the ptrace branch January 12, 2026 03:23

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

ptrace #129

ptrace #129

Uh oh!

arihant2math commented Jan 5, 2026 •

edited

Loading

Uh oh!

hexagonal-sun commented Jan 11, 2026 •

edited

Loading

Uh oh!

arihant2math left a comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

ptrace #129

ptrace #129

Uh oh!

Conversation

arihant2math commented Jan 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

hexagonal-sun commented Jan 11, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

arihant2math left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

arihant2math commented Jan 5, 2026 •

edited

Loading

hexagonal-sun commented Jan 11, 2026 •

edited

Loading