Commit 6fed025f authored by Namhyung Kim's avatar Namhyung Kim
Browse files

perf dwarf-aux: Add die_get_cfa() 



The die_get_cfa() is to get frame base register and offset at the given
instruction address (pc).  This info will be used to locate stack
variables which have location expression using DW_OP_fbreg.

Reviewed-by: default avatarIan Rogers <irogers@google.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20240117062657.985479-8-namhyung@kernel.org


Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 5f7cdde8

tools/perf/util/dwarf-aux.c

+67 −1
Original line number Diff line number Diff line
@@ -1407,7 +1407,73 @@ Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc, 
		*offset = data.offset;

	return result;

}

#endif

#endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */



#ifdef HAVE_DWARF_CFI_SUPPORT

static int reg_from_dwarf_op(Dwarf_Op *op)

{

	switch (op->atom) {

	case DW_OP_reg0 ... DW_OP_reg31:

		return op->atom - DW_OP_reg0;

	case DW_OP_breg0 ... DW_OP_breg31:

		return op->atom - DW_OP_breg0;

	case DW_OP_regx:

	case DW_OP_bregx:

		return op->number;

	default:

		break;

	}

	return -1;

}



static int offset_from_dwarf_op(Dwarf_Op *op)

{

	switch (op->atom) {

	case DW_OP_reg0 ... DW_OP_reg31:

	case DW_OP_regx:

		return 0;

	case DW_OP_breg0 ... DW_OP_breg31:

		return op->number;

	case DW_OP_bregx:

		return op->number2;

	default:

		break;

	}

	return -1;

}



/**

 * die_get_cfa - Get frame base information

 * @dwarf: a Dwarf info

 * @pc: program address

 * @preg: pointer for saved register

 * @poffset: pointer for saved offset

 *

 * This function gets register and offset for CFA (Canonical Frame Address)

 * by searching the CIE/FDE info.  The CFA usually points to the start address

 * of the current stack frame and local variables can be located using an offset

 * from the CFA.  The @preg and @poffset will be updated if it returns 0.

 */

int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset)

{

	Dwarf_CFI *cfi;

	Dwarf_Frame *frame = NULL;

	Dwarf_Op *ops = NULL;

	size_t nops;



	cfi = dwarf_getcfi(dwarf);

	if (cfi == NULL)

		return -1;



	if (!dwarf_cfi_addrframe(cfi, pc, &frame) &&

	    !dwarf_frame_cfa(frame, &ops, &nops) && nops == 1) {

		*preg = reg_from_dwarf_op(ops);

		*poffset = offset_from_dwarf_op(ops);

		return 0;

	}

	return -1;

}

#endif /* HAVE_DWARF_CFI_SUPPORT */



/*

 * die_has_loclist - Check if DW_AT_location of @vr_die is a location list

tools/perf/util/dwarf-aux.h

+15 −0
Original line number Diff line number Diff line
@@ -177,4 +177,19 @@ static inline Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die __maybe_unu 


#endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */



#ifdef HAVE_DWARF_CFI_SUPPORT



/* Get the frame base information from CFA */

int die_get_cfa(Dwarf *dwarf, u64 pc, int *preg, int *poffset);



#else /* HAVE_DWARF_CFI_SUPPORT */



static inline int die_get_cfa(Dwarf *dwarf __maybe_unused, u64 pc __maybe_unused,

			      int *preg __maybe_unused, int *poffset __maybe_unused)

{

	return -1;

}



#endif /* HAVE_DWARF_CFI_SUPPORT */



#endif /* _DWARF_AUX_H */