linux-kernel - [PATCH] pfn_t: force '~' to be parsed as an unary operator

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Date:   Sun, 21 Oct 2018 10:59:39 -0400
From:   Sebastien Boisvert <sebhtml@...eotron.qc.ca>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Sebastien Boisvert <sebhtml@...eotron.qc.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@...il.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ross Zwisler <zwisler@...nel.org>,
        Elenie Godzaridis <arangradient@...il.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] pfn_t: force '~' to be parsed as an unary operator

Tracing the event "fs_dax:dax_pmd_insert_mapping" with perf produces this
warning:
      [fs_dax:dax_pmd_insert_mapping] unknown op '~'

It is printed in process_op (tools/lib/traceevent/event-parse.c) because '~'
is parsed as a binary operator.

perf reads the format of fs_dax:dax_pmd_insert_mapping ("print fmt") from
/sys/kernel/debug/tracing/events/fs_dax/dax_pmd_insert_mapping/format .

The format contains:

~(((u64) ~(~(((1UL) << 12)-1)))
         ^
         \ interpreted as a binary operator by process_op().

This part is generated in the declaration of the event class
dax_pmd_insert_mapping_class in include/trace/events/fs_dax.h :

		__print_flags_u64(__entry->pfn_val & PFN_FLAGS_MASK, "|",
			PFN_FLAGS_TRACE),

This patch adds a pair of parentheses in the declaration of PFN_FLAGS_MASK to
make sure that '~' is parsed as a unary operator by perf.

The part of the format that was problematic is now:

~(((u64) (~(~(((1UL) << 12)-1))))

Now, all the '~' are parsed as unary operators.

Cc: Dan Williams <dan.j.williams@...el.com>
Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@...il.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Ross Zwisler <zwisler@...nel.org>
Cc: Elenie Godzaridis <arangradient@...il.com>
Cc: linux-perf-users@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Sebastien Boisvert <sebhtml@...eotron.qc.ca>
---
 include/linux/pfn_t.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/pfn_t.h b/include/linux/pfn_t.h
index 21713dc14ce2..673546ba7342 100644
--- a/include/linux/pfn_t.h
+++ b/include/linux/pfn_t.h
@@ -10,7 +10,7 @@
  * PFN_DEV - pfn is not covered by system memmap by default
  * PFN_MAP - pfn has a dynamic page mapping established by a device driver
  */
-#define PFN_FLAGS_MASK (((u64) ~PAGE_MASK) << (BITS_PER_LONG_LONG - PAGE_SHIFT))
+#define PFN_FLAGS_MASK (((u64) (~PAGE_MASK)) << (BITS_PER_LONG_LONG - PAGE_SHIFT))
 #define PFN_SG_CHAIN (1ULL << (BITS_PER_LONG_LONG - 1))
 #define PFN_SG_LAST (1ULL << (BITS_PER_LONG_LONG - 2))
 #define PFN_DEV (1ULL << (BITS_PER_LONG_LONG - 3))
-- 
2.17.1