Date: Fri, 23 Dec 2016 03:27:11 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r310445 - in head/sys/mips: include mips Message-ID: <201612230327.uBN3RBC1099442@repo.freebsd.org>
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Author: jhb Date: Fri Dec 23 03:27:11 2016 New Revision: 310445 URL: https://svnweb.freebsd.org/changeset/base/310445 Log: Teach DDB how to unwind across a kernel stack overflow. Kernel stack overflows in MIPS call panic() directly from an assembly handler after storing the interrupted context's registers in a trapframe. Rather than inferring the location of ra, sp, and pc from the instruction stream, recognize the pc of a kernel stack overflow and pull the registers from the trapframe. Sponsored by: DARPA / AFRL Modified: head/sys/mips/include/trap.h head/sys/mips/mips/db_trace.c head/sys/mips/mips/exception.S Modified: head/sys/mips/include/trap.h ============================================================================== --- head/sys/mips/include/trap.h Fri Dec 23 03:23:14 2016 (r310444) +++ head/sys/mips/include/trap.h Fri Dec 23 03:27:11 2016 (r310445) @@ -111,6 +111,7 @@ void trapDump(char *msg); void MipsFPTrap(u_int, u_int, u_int); void MipsKernGenException(void); void MipsKernIntr(void); +void MipsKStackOverflow(void); void MipsTLBInvalidException(void); void MipsTLBMissException(void); void MipsUserGenException(void); Modified: head/sys/mips/mips/db_trace.c ============================================================================== --- head/sys/mips/mips/db_trace.c Fri Dec 23 03:23:14 2016 (r310444) +++ head/sys/mips/mips/db_trace.c Fri Dec 23 03:27:11 2016 (r310445) @@ -36,6 +36,7 @@ __FBSDID("$FreeBSD$"); #include <sys/stack.h> #include <sys/sysent.h> +#include <machine/asm.h> #include <machine/db_machdep.h> #include <machine/md_var.h> #include <machine/mips_opcode.h> @@ -157,7 +158,6 @@ loop: valid_args[2] = 0; valid_args[3] = 0; next_ra = 0; -/* Jump here after a nonstandard (interrupt handler) frame */ stksize = 0; subr = 0; if (frames++ > 100) { @@ -213,6 +213,15 @@ loop: ra = 0; goto done; } + + /* + * For a kernel stack overflow, skip to the output and + * afterwards pull the previous registers out of the trapframe + * instead of decoding the function prologue. + */ + if (pc == (uintptr_t)MipsKStackOverflow) + goto done; + /* * Find the beginning of the current subroutine by scanning * backwards from the current PC for the end of the previous @@ -389,7 +398,21 @@ done: (uintmax_t)(u_register_t) sp, stksize); - if (ra) { + if (pc == (uintptr_t)MipsKStackOverflow) { +#define TF_REG(base, reg) ((base) + CALLFRAME_SIZ + ((reg) * SZREG)) +#if defined(__mips_n64) || defined(__mips_n32) + pc = kdbpeekd((int *)TF_REG(sp, PC)); + ra = kdbpeekd((int *)TF_REG(sp, RA)); + sp = kdbpeekd((int *)TF_REG(sp, SP)); +#else + pc = kdbpeek((int *)TF_REG(sp, PC)); + ra = kdbpeek((int *)TF_REG(sp, RA)); + sp = kdbpeek((int *)TF_REG(sp, SP)); +#endif +#undef TF_REG + (*printfn) ("--- Kernel Stack Overflow ---\n"); + goto loop; + } else if (ra) { if (pc == ra && stksize == 0) (*printfn) ("stacktrace: loop!\n"); else { Modified: head/sys/mips/mips/exception.S ============================================================================== --- head/sys/mips/mips/exception.S Fri Dec 23 03:23:14 2016 (r310444) +++ head/sys/mips/mips/exception.S Fri Dec 23 03:27:11 2016 (r310445) @@ -1019,6 +1019,8 @@ tlb_insert_random: * of this handler. Otherwise the ddb backtrace code will think that * the panic() was called from MipsTLBMissException. */ + .globl MipsKStackOverflow +MipsKStackOverflow: nop .set pop
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