From 1c26c382c9e7a6a919b5a005e07747c40366e7df Mon Sep 17 00:00:00 2001 From: James Hogan Date: Thu, 30 Mar 2017 16:06:02 +0100 Subject: [PATCH] MIPS: KGDB: Use kernel context for sleeping threads commit 162b270c664dca2e0944308e92f9fcc887151a72 upstream. KGDB is a kernel debug stub and it can't be used to debug userland as it can only safely access kernel memory. On MIPS however KGDB has always got the register state of sleeping processes from the userland register context at the beginning of the kernel stack. This is meaningless for kernel threads (which never enter userland), and for user threads it prevents the user seeing what it is doing while in the kernel: (gdb) info threads Id Target Id Frame ... 3 Thread 2 (kthreadd) 0x0000000000000000 in ?? () 2 Thread 1 (init) 0x000000007705c4b4 in ?? () 1 Thread -2 (shadowCPU0) 0xffffffff8012524c in arch_kgdb_breakpoint () at arch/mips/kernel/kgdb.c:201 Get the register state instead from the (partial) kernel register context stored in the task's thread_struct for resume() to restore. All threads now correctly appear to be in context_switch(): (gdb) info threads Id Target Id Frame ... 3 Thread 2 (kthreadd) context_switch (rq=, cookie=..., next=, prev=0x0) at kernel/sched/core.c:2903 2 Thread 1 (init) context_switch (rq=, cookie=..., next=, prev=0x0) at kernel/sched/core.c:2903 1 Thread -2 (shadowCPU0) 0xffffffff8012524c in arch_kgdb_breakpoint () at arch/mips/kernel/kgdb.c:201 Call clobbered registers which aren't saved and exception registers (BadVAddr & Cause) which can't be easily determined without stack unwinding are reported as 0. The PC is taken from the return address, such that the state presented matches that found immediately after returning from resume(). Fixes: 8854700115ec ("[MIPS] kgdb: add arch support for the kernel's kgdb core") Signed-off-by: James Hogan Cc: Jason Wessel Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/15829/ Signed-off-by: Ralf Baechle Signed-off-by: Greg Kroah-Hartman --- arch/mips/kernel/kgdb.c | 48 ++++++++++++++++++++++++++++------------- 1 file changed, 33 insertions(+), 15 deletions(-) diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c index de63d36af895..732d6171ac6a 100644 --- a/arch/mips/kernel/kgdb.c +++ b/arch/mips/kernel/kgdb.c @@ -244,9 +244,6 @@ static int compute_signal(int tt) void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p) { int reg; - struct thread_info *ti = task_thread_info(p); - unsigned long ksp = (unsigned long)ti + THREAD_SIZE - 32; - struct pt_regs *regs = (struct pt_regs *)ksp - 1; #if (KGDB_GDB_REG_SIZE == 32) u32 *ptr = (u32 *)gdb_regs; #else @@ -254,25 +251,46 @@ void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p) #endif for (reg = 0; reg < 16; reg++) - *(ptr++) = regs->regs[reg]; + *(ptr++) = 0; /* S0 - S7 */ - for (reg = 16; reg < 24; reg++) - *(ptr++) = regs->regs[reg]; + *(ptr++) = p->thread.reg16; + *(ptr++) = p->thread.reg17; + *(ptr++) = p->thread.reg18; + *(ptr++) = p->thread.reg19; + *(ptr++) = p->thread.reg20; + *(ptr++) = p->thread.reg21; + *(ptr++) = p->thread.reg22; + *(ptr++) = p->thread.reg23; for (reg = 24; reg < 28; reg++) *(ptr++) = 0; /* GP, SP, FP, RA */ - for (reg = 28; reg < 32; reg++) - *(ptr++) = regs->regs[reg]; - - *(ptr++) = regs->cp0_status; - *(ptr++) = regs->lo; - *(ptr++) = regs->hi; - *(ptr++) = regs->cp0_badvaddr; - *(ptr++) = regs->cp0_cause; - *(ptr++) = regs->cp0_epc; + *(ptr++) = (long)p; + *(ptr++) = p->thread.reg29; + *(ptr++) = p->thread.reg30; + *(ptr++) = p->thread.reg31; + + *(ptr++) = p->thread.cp0_status; + + /* lo, hi */ + *(ptr++) = 0; + *(ptr++) = 0; + + /* + * BadVAddr, Cause + * Ideally these would come from the last exception frame up the stack + * but that requires unwinding, otherwise we can't know much for sure. + */ + *(ptr++) = 0; + *(ptr++) = 0; + + /* + * PC + * use return address (RA), i.e. the moment after return from resume() + */ + *(ptr++) = p->thread.reg31; } void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc) -- 2.20.1