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Various fixes for the MIPS DDB stack unwinder.

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- Fix kernel stack unwinding end-of-function false-positive

  The kernel stack unwinder assumes that any jr $ra indicates the end
  of the current function. However, modern compilers generate code
  that contains jr $ra at various places inside the function.

- Handle LLD inter-function padding when looking for the start of a
  function.

- Use call site for symbol name/offset when unwinding

  Currently we use the return address, which will normally just give
  an output that's off by 8 from the actual call site.  However, for
  tail calls, this is particularly bad, as we end up printing the
  symbol name for the function that comes after the one that made the
  call.  Instead we should go back two instructions from the return
  address for the unwound program counter.

Submitted by:   arichardson (1, 2), jrtc27 (3)
Reviewed by:	arichardson
Obtained from:	CheriBSD
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D27363
This commit is contained in:
John Baldwin 2020-12-04 20:14:25 +00:00
parent 353ce81687
commit a1d505eaba
1 changed files with 25 additions and 15 deletions
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40
sys/mips/mips/db_trace.c
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@ -67,11 +67,10 @@ extern char edata[];
|| (((ins) & 0xffff8000) == 0x67bd8000))
/*
* MIPS ABI 3.0 requires that all functions return using the 'j ra' instruction
*
* XXX gcc doesn't do this for functions with __noreturn__ attribute.
* LLD will insert invalid instruction traps between functions.
* Currently this is 0xefefefef but it may change in the future.
*/
#define MIPS_END_OF_FUNCTION(ins) ((ins) == 0x03e00008)
#define MIPS_LLD_PADDING_BETWEEN_FUNCTIONS(ins) ((ins) == 0xefefefef)
#if defined(__mips_n64)
# define MIPS_IS_VALID_KERNELADDR(reg) ((((reg) & 3) == 0) && \
@ -183,27 +182,32 @@ stacktrace_subr(register_t pc, register_t sp, register_t ra)
* subroutine.
*/
if (!subr) {
va = pc - sizeof(int);
va = pc;
while (1) {
instr = kdbpeek((int *)va);
/* LLD fills padding between functions with 0xefefefef */
if (MIPS_LLD_PADDING_BETWEEN_FUNCTIONS(instr))
break;
if (MIPS_START_OF_FUNCTION(instr))
break;
if (MIPS_END_OF_FUNCTION(instr)) {
/* skip over branch-delay slot instruction */
va += 2 * sizeof(int);
break;
}
va -= sizeof(int);
}
/* skip over nulls which might separate .o files */
while ((instr = kdbpeek((int *)va)) == 0)
/*
* Skip over nulls/trap padding which might separate
* object files or functions.
*/
instr = kdbpeek((int *)va);
while (instr == 0 || MIPS_LLD_PADDING_BETWEEN_FUNCTIONS(instr)) {
va += sizeof(int);
instr = kdbpeek((int *)va);
}
subr = va;
}
/* scan forwards to find stack size and any saved registers */
stksize = 0;
more = 3;
@ -374,10 +378,16 @@ stacktrace_subr(register_t pc, register_t sp, register_t ra)
(uintmax_t)cause, (uintmax_t)badvaddr);
goto loop;
} else if (ra) {
if (pc == ra && stksize == 0)
/*
* We subtract two instructions from ra to convert it
* from a return address to a calling address,
* accounting for the delay slot.
*/
register_t next_pc = ra - 2 * sizeof(int);
if (pc == next_pc && stksize == 0)
db_printf("stacktrace: loop!\n");
else {
pc = ra;
pc = next_pc;
sp += stksize;
ra = next_ra;
goto loop;