| Message ID | 20201028122102.24202-1-lukas.bulwahn@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86/unwind: remove unneeded initialization | expand |
On Wed, Oct 28, 2020 at 01:21:02PM +0100, Lukas Bulwahn wrote: > 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@gmail.com> Seems fine to me. Reviewed-by: Nathan Chancellor <natechancellor@gmail.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 > -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#135): https://lists.elisa.tech/g/linux-safety/message/135 Mute This Topic: https://lists.elisa.tech/mt/77861405/4688437 Group Owner: linux-safety+owner@lists.elisa.tech Unsubscribe: https://lists.elisa.tech/g/linux-safety/unsub [patchwork-linux-safety@patchwork.kernel.org] -=-=-=-=-=-=-=-=-=-=-=-
this looks like a reimplementation of bsearch() perhaps the maintainer can add a comment why the kernel implementation is not suitable here ? jm2c wh
On Thu, Oct 29, 2020 at 11:49:50AM +0000, Walter Harms wrote: > this looks like a reimplementation of bsearch() > perhaps the maintainer can add a comment why the > kernel implementation is not suitable here ? If you look carefully it doesn't do an exact match, which is what bsearch() does. bsearch() also isn't stable in the precense of duplicates. -=-=-=-=-=-=-=-=-=-=-=- Links: You receive all messages sent to this group. View/Reply Online (#138): https://lists.elisa.tech/g/linux-safety/message/138 Mute This Topic: https://lists.elisa.tech/mt/77861405/4688437 Group Owner: linux-safety+owner@lists.elisa.tech Unsubscribe: https://lists.elisa.tech/g/linux-safety/unsub [patchwork-linux-safety@patchwork.kernel.org] -=-=-=-=-=-=-=-=-=-=-=-
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;
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@gmail.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(-)