linux-kernel - AW: [PATCH] x86/unwind: remove unneeded initialization

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Date:   Thu, 29 Oct 2020 11:49:50 +0000
From:   Walter Harms <wharms@....de>
To:     Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-safety@...ts.elisa.tech" <linux-safety@...ts.elisa.tech>
Subject: AW: [PATCH] x86/unwind: remove unneeded initialization

this looks like a reimplementation of bsearch()
perhaps the maintainer can add a comment why the 
kernel implementation is not suitable here ?

jm2c
wh

________________________________________
Von: Lukas Bulwahn [lukas.bulwahn@...il.com]
Gesendet: Mittwoch, 28. Oktober 2020 13:21
An: Thomas Gleixner; Ingo Molnar; Borislav Petkov; Josh Poimboeuf; x86@...nel.org
Cc: H . Peter Anvin; Peter Zijlstra; Nathan Chancellor; Nick Desaulniers; linux-kernel@...r.kernel.org; clang-built-linux@...glegroups.com; kernel-janitors@...r.kernel.org; linux-safety@...ts.elisa.tech; Lukas Bulwahn
Betreff: [PATCH] x86/unwind: remove unneeded initialization

make clang-analyzer on x86_64 defconfig caught my attention with:

  arch/x86/kernel/unwind_orc.c:38:7: warning: Value stored to 'mid' during
  its initialization is never read [clang-analyzer-deadcode.DeadStores]
          int *mid = first, *found = first;
               ^

Commit ee9f8fce9964 ("x86/unwind: Add the ORC unwinder") introduced
__orc_find() with this unneeded dead-store initialization.

Put the variable in local scope and initialize only once the value is
needed to make clang-analyzer happy.

As compilers will detect this unneeded assignment and optimize this
anyway, the resulting object code is effectively identical before and
after this change.

No functional change. Effectively, no change to object code.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@...il.com>
---
applies cleanly on current master and next-20201028

Josh, please ack.
Ingo, Borislav, please pick this minor non-urgent clean-up patch.

 arch/x86/kernel/unwind_orc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 6a339ce328e0..5c64eed08257 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -35,7 +35,7 @@ static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
 {
        int *first = ip_table;
        int *last = ip_table + num_entries - 1;
-       int *mid = first, *found = first;
+       int *found = first;

        if (!num_entries)
                return NULL;
@@ -47,7 +47,7 @@ static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
         * ignored when they conflict with a real entry.
         */
        while (first <= last) {
-               mid = first + ((last - first) / 2);
+               int *mid = first + ((last - first) / 2);

                if (orc_ip(mid) <= ip) {
                        found = mid;
--
2.17.1