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Commit 69123184 authored by Michael Neuling's avatar Michael Neuling Committed by Benjamin Herrenschmidt
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powerpc/perf: Fix setting of "to" addresses for BHRB 



Currently we only set the "to" address in the branch stack when the CPU
explicitly gives us a value.  Unfortunately it only does this for XL form
branches (eg blr, bctr, bctar) and not I and B form branches (eg b, bc).

Fortunately if we read the instruction from memory we can extract the offset of
a branch and calculate the target address.

This adds a function power_pmu_bhrb_to() to calculate the target/to address of
the corresponding I and B form branches.  It handles branches in both user and
kernel spaces.  It also plumbs this into the perf brhb reading code.

Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 506e70d1

arch/powerpc/perf/core-book3s.c

+30 −1
Original line number Diff line number Diff line
@@ -13,11 +13,13 @@ 
#include <linux/perf_event.h>

#include <linux/percpu.h>

#include <linux/hardirq.h>

#include <linux/uaccess.h>

#include <asm/reg.h>

#include <asm/pmc.h>

#include <asm/machdep.h>

#include <asm/firmware.h>

#include <asm/ptrace.h>

#include <asm/code-patching.h>



#define BHRB_MAX_ENTRIES	32

#define BHRB_TARGET		0x0000000000000002
@@ -362,6 +364,32 @@ void power_pmu_flush_branch_stack(void) 
	if (ppmu->bhrb_nr)

		power_pmu_bhrb_reset();

}

/* Calculate the to address for a branch */

static __u64 power_pmu_bhrb_to(u64 addr)

{

	unsigned int instr;

	int ret;

	__u64 target;



	if (is_kernel_addr(addr))

		return branch_target((unsigned int *)addr);



	/* Userspace: need copy instruction here then translate it */

	pagefault_disable();

	ret = __get_user_inatomic(instr, (unsigned int __user *)addr);

	if (ret) {

		pagefault_enable();

		return 0;

	}

	pagefault_enable();



	target = branch_target(&instr);

	if ((!target) || (instr & BRANCH_ABSOLUTE))

		return target;



	/* Translate relative branch target from kernel to user address */

	return target - (unsigned long)&instr + addr;

}



/* Processing BHRB entries */

void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
@@ -426,7 +454,8 @@ void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw) 
				/* Branches to immediate field 

				   (ie I or B form) */

				cpuhw->bhrb_entries[u_index].from = addr;

				cpuhw->bhrb_entries[u_index].to = 0;

				cpuhw->bhrb_entries[u_index].to =

					power_pmu_bhrb_to(addr);

				cpuhw->bhrb_entries[u_index].mispred = pred;

				cpuhw->bhrb_entries[u_index].predicted = ~pred;

			}