* Break on syscall? @ 2006-05-19 10:59 Alex Bennee 2006-05-19 13:43 ` Daniel Jacobowitz 0 siblings, 1 reply; 6+ messages in thread From: Alex Bennee @ 2006-05-19 10:59 UTC (permalink / raw) To: gdb Is it possible to get gdb to break on entering/exiting a syscall (rather than breaking on entering libc or some such)? Does gdb use ptrace() to control breakpoints in the debugged code? -- Alex, homepage: http://www.bennee.com/~alex/ Famous, adj.: Conspicuously miserable. -- Ambrose Bierce ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall? 2006-05-19 10:59 Break on syscall? Alex Bennee @ 2006-05-19 13:43 ` Daniel Jacobowitz 2006-05-19 22:06 ` Mark Kettenis 0 siblings, 1 reply; 6+ messages in thread From: Daniel Jacobowitz @ 2006-05-19 13:43 UTC (permalink / raw) To: Alex Bennee; +Cc: gdb On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote: > Is it possible to get gdb to break on entering/exiting a syscall (rather > than breaking on entering libc or some such)? This is not supported. > Does gdb use ptrace() to > control breakpoints in the debugged code? Breakpoints are inserted usually using PTRACE_POKETEXT. -- Daniel Jacobowitz CodeSourcery ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall? 2006-05-19 13:43 ` Daniel Jacobowitz @ 2006-05-19 22:06 ` Mark Kettenis 2006-05-19 23:13 ` Daniel Jacobowitz 0 siblings, 1 reply; 6+ messages in thread From: Mark Kettenis @ 2006-05-19 22:06 UTC (permalink / raw) To: drow; +Cc: kernel-hacker, gdb > Date: Fri, 19 May 2006 08:48:35 -0400 > From: Daniel Jacobowitz <drow@false.org> > > On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote: > > Is it possible to get gdb to break on entering/exiting a syscall (rather > > than breaking on entering libc or some such)? > > This is not supported. But I think it would be nice if we would support something like "catch syscall", just like we support "catch fork". Mark ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall? 2006-05-19 22:06 ` Mark Kettenis @ 2006-05-19 23:13 ` Daniel Jacobowitz 2006-05-20 3:00 ` PAUL GILLIAM 0 siblings, 1 reply; 6+ messages in thread From: Daniel Jacobowitz @ 2006-05-19 23:13 UTC (permalink / raw) To: Mark Kettenis; +Cc: kernel-hacker, gdb On Fri, May 19, 2006 at 11:16:15PM +0200, Mark Kettenis wrote: > > Date: Fri, 19 May 2006 08:48:35 -0400 > > From: Daniel Jacobowitz <drow@false.org> > > > > On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote: > > > Is it possible to get gdb to break on entering/exiting a syscall (rather > > > than breaking on entering libc or some such)? > > > > This is not supported. > > But I think it would be nice if we would support something like "catch > syscall", just like we support "catch fork". Yes, probably. I think I even started work on this once. It's just a bit trickier. Not only do you want to be able to decode arguments, but there are other problems... for example, I think procfs allows it, but traditionally ptrace has no way to request a single step and stop if entering a syscall, so you'd need an arch hook to detect it to handle that case. A nice project for some rainy month :-) -- Daniel Jacobowitz CodeSourcery ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall? 2006-05-19 23:13 ` Daniel Jacobowitz @ 2006-05-20 3:00 ` PAUL GILLIAM 2006-05-21 13:25 ` Daniel Jacobowitz 0 siblings, 1 reply; 6+ messages in thread From: PAUL GILLIAM @ 2006-05-20 3:00 UTC (permalink / raw) To: Daniel Jacobowitz; +Cc: Mark Kettenis, kernel-hacker, gdb On Fri, 2006-05-19 at 18:05 -0400, Daniel Jacobowitz wrote: > On Fri, May 19, 2006 at 11:16:15PM +0200, Mark Kettenis wrote: > > > Date: Fri, 19 May 2006 08:48:35 -0400 > > > From: Daniel Jacobowitz <drow@false.org> > > > > > > On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote: > > > > Is it possible to get gdb to break on entering/exiting a syscall (rather > > > > than breaking on entering libc or some such)? > > > > > > This is not supported. > > > > But I think it would be nice if we would support something like "catch > > syscall", just like we support "catch fork". > > Yes, probably. I think I even started work on this once. It's just a > bit trickier. Not only do you want to be able to decode arguments, but > there are other problems... for example, I think procfs allows it, but > traditionally ptrace has no way to request a single step and stop if > entering a syscall, so you'd need an arch hook to detect it to handle > that case. > > A nice project for some rainy month :-) > From the ptrace(2) man page on Linux: PTRACE_SYSCALL, PTRACE_SINGLESTEP Restarts the stopped child as for PTRACE_CONT, but arranges for the child to be stopped at the next entry to or exit from a sys- tem call, or after execution of a single instruction, respec- tively. (The child will also, as usual, be stopped upon receipt of a signal.) From the parent’s perspective, the child will appear to have been stopped by receipt of a SIGTRAP. So, for PTRACE_SYSCALL, for example, the idea is to inspect the argu- ments to the system call at the first stop, then do another PTRACE_SYSCALL and inspect the return value of the system call at the second stop. (addr is ignored.) The 'ltrace' utility uses this to trace system calls. It uses a sleazy table (/etc/ltrace.cfg) to find out about their arguments... GDB should be able to do a much better job, although matching syscall numbers to their associated library routines would be a challenge (at least for me 8-) -=# Paul #=- PS: Here in Oregon, rainy months are the norm 8-) ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall? 2006-05-20 3:00 ` PAUL GILLIAM @ 2006-05-21 13:25 ` Daniel Jacobowitz 0 siblings, 0 replies; 6+ messages in thread From: Daniel Jacobowitz @ 2006-05-21 13:25 UTC (permalink / raw) To: PAUL GILLIAM; +Cc: Mark Kettenis, kernel-hacker, gdb On Fri, May 19, 2006 at 03:09:31PM -0700, PAUL GILLIAM wrote: > > traditionally ptrace has no way to request a single step and stop if > > entering a syscall, so you'd need an arch hook to detect it to handle > > that case. > From the ptrace(2) man page on Linux: > > PTRACE_SYSCALL, PTRACE_SINGLESTEP That doesn't conflict with what I said. You can't issue PTRACE_SYSCALL and PTRACE_SINGLESTEP at the same time. > The 'ltrace' utility uses this to trace system calls. It uses a sleazy > table (/etc/ltrace.cfg) to find out about their arguments... GDB should > be able to do a much better job, although matching syscall numbers to > their associated library routines would be a challenge (at least for me > 8-) GDB can do vastly better, but it's not a small project. -- Daniel Jacobowitz CodeSourcery ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2006-05-20 0:18 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2006-05-19 10:59 Break on syscall? Alex Bennee 2006-05-19 13:43 ` Daniel Jacobowitz 2006-05-19 22:06 ` Mark Kettenis 2006-05-19 23:13 ` Daniel Jacobowitz 2006-05-20 3:00 ` PAUL GILLIAM 2006-05-21 13:25 ` Daniel Jacobowitz
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