Messages in this thread | | | Date | Wed, 30 Apr 2014 15:35:33 +0200 (CEST) | From | Mark Kettenis <> | Subject | Re: [PATCH] Fix get ERESTARTSYS with m32 in x86_64 when debug by GDB |
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> Date: Tue, 29 Apr 2014 22:10:15 -0700 > From: "H. Peter Anvin" <hpa@zytor.com> > > On 04/29/2014 10:08 PM, Andrew Pinski wrote: > > > > restoring the values is hard since even the ptrace interface does not > > allow for that. > > > > So that begs the ultimate question, which is: given the fact that there > is *state missing* from the state vector (this is the core of the > problem), is there a way we can add that state so that gdb will be able > to save and restore it?
Carrying around additional state in GDB is complicated; I'd rather avoid it.
arch/x86/kernel/ptrace.c:putreg32() has this bit of code:
case offsetof(struct user32, regs.orig_eax): /* * A 32-bit debugger setting orig_eax means to restore * the state of the task restarting a 32-bit syscall. * Make sure we interpret the -ERESTART* codes correctly * in case the task is not actually still sitting at the * exit from a 32-bit syscall with TS_COMPAT still set. */ regs->orig_ax = value; if (syscall_get_nr(child, regs) >= 0) task_thread_info(child)->status |= TS_COMPAT; break;
which gets used for 32-bit compat ptrace(2). Perhaps the same logic should be added to putreg() if the child is a 32-bit process?
If (and only if) the goal of that TS_COMPAT flag solely is to trigger the error code sign-extension in arch/x86/asm/syscall.h:syscall_get_error(), we could work around to problem in GDB by checking "orig_ax" to see if we're continuing an interrupted system call and sign extend the error code in the real "eax" register if we are.
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