diff options
Diffstat (limited to 'gitlab/issues_text/target_missing/host_missing/accel_missing/654')
| -rw-r--r-- | gitlab/issues_text/target_missing/host_missing/accel_missing/654 | 23 |
1 files changed, 0 insertions, 23 deletions
diff --git a/gitlab/issues_text/target_missing/host_missing/accel_missing/654 b/gitlab/issues_text/target_missing/host_missing/accel_missing/654 deleted file mode 100644 index 818a62a51..000000000 --- a/gitlab/issues_text/target_missing/host_missing/accel_missing/654 +++ /dev/null @@ -1,23 +0,0 @@ -Strace Log Output Mangled -Description of problem: -The syscall log entries from the strace logging capability can be interrupted by other log messages before the full syscall line is -complete. -This makes parsing the strace syscall lines from the log output difficult. -Steps to reproduce: -1. Run the supplied command with a simple dynamically linked binary, or a binary that performs mmaps -2. Notice that the strace 'mmap' syscall log entries in the trace file are interrupted by the page log output -Additional information: -I have attached an example log from a dynamically linked 'hello world' binary, which demonstrates the bug in the mmap syscall strace entries. [output.trace](/uploads/88c83273582d00241fbf95af735dcc61/output.trace) - - -I believe this bug caused by a couple of things: -Firstly, in the linux-user/syscall.c file: the strace syscall entry is not output atomically, but instead split across two calls: -The first half is at `print_syscall`: https://gitlab.com/qemu-project/qemu/-/blob/master/linux-user/syscall.c#L13153 -And the return value (and new line) is printed in `print_syscall_ret`: https://gitlab.com/qemu-project/qemu/-/blob/master/linux-user/syscall.c#L13160 - -In the case of the mmap syscall, the function `log_page_dump` is called between these two functions resulting in the mangled log output: -https://gitlab.com/qemu-project/qemu/-/blob/master/linux-user/mmap.c#L633 -There may be other syscalls that behave similarly, but this was noticed due to the mmap behavior. - - -Internally to the `print_syscall` and `print_syscall_ret` functions, `qemu_log` is called multiple times to compose the full log entry, and it seems that it is inside `qemu_log` that the logfile lock is obtained and dropped - so theoretically another thread can output to the log during the printing of a single syscall entry between these `qemu_log` calls. I do not know if this actually happens in practice besides the mmap scenario described above. |