From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yann Droneaud Date: Fri, 30 May 2014 20:02:47 +0000 Subject: [PATCH] driver core/platform: remove unused implicit padding in platform_object Message-Id: <1401480167-15091-1-git-send-email-ydroneaud@opteya.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: linux-arm-kernel@lists.infradead.org Up to 7 bytes are wasted at the end of struct platform_object in the form of padding after name field: unfortunately this padding is not used when allocating the memory to hold the name. This patch converts name array from name[1] to C99 flexible array name[] (equivalent to name[0]) so that no padding is required by the presence of this field. Memory allocation is updated to take care of allocating an additional byte for the NUL terminating character. Built on Fedora 20, using GCC 4.8, for ARM, i386, SPARC64 and x86_64 architectures, the data structure layout can be reported with following command: $ pahole drivers/base/platform.o \ --recursive \ --class_name device,pdev_archdata,platform_device,platform_object Please find below some comparisons of structure layout for arm, i386, sparc64 and x86_64 architecture before and after the patch. --- obj-arm/drivers/base/platform.o.pahole.v3.15-rc7-79-gfe45736f4134 201= 4-05-30 10:32:06.290960701 +0200 +++ obj-arm/drivers/base/platform.o.pahole.v3.15-rc7-80-g2cdb06858d71 201= 4-05-30 11:26:20.851988347 +0200 @@ -81,10 +81,9 @@ /* XXX last struct has 4 bytes of padding */ /* --- cacheline 6 boundary (384 bytes) was 8 bytes ago --- */ - char name[1]; /* 392 1 */ + char name[0]; /* 392 0 */ - /* size: 400, cachelines: 7, members: 2 */ - /* padding: 7 */ + /* size: 392, cachelines: 7, members: 2 */ /* paddings: 1, sum paddings: 4 */ - /* last cacheline: 16 bytes */ + /* last cacheline: 8 bytes */ }; --- obj-i386/drivers/base/platform.o.pahole.v3.15-rc7-79-gfe45736f4134 20= 14-05-30 10:32:06.305960691 +0200 +++ obj-i386/drivers/base/platform.o.pahole.v3.15-rc7-80-g2cdb06858d71 20= 14-05-30 11:26:20.875988332 +0200 @@ -73,9 +73,8 @@ struct platform_object { struct platform_device pdev; /* 0 396 */ /* --- cacheline 6 boundary (384 bytes) was 12 bytes ago --- */ - char name[1]; /* 396 1 */ + char name[0]; /* 396 0 */ - /* size: 400, cachelines: 7, members: 2 */ - /* padding: 3 */ - /* last cacheline: 16 bytes */ + /* size: 396, cachelines: 7, members: 2 */ + /* last cacheline: 12 bytes */ }; --- obj-sparc64/drivers/base/platform.o.pahole.v3.15-rc7-79-gfe45736f4134= 2014-05-30 10:32:06.406960625 +0200 +++ obj-sparc64/drivers/base/platform.o.pahole.v3.15-rc7-80-g2cdb06858d71= 2014-05-30 11:26:20.971988269 +0200 @@ -94,9 +94,8 @@ struct platform_object { struct platform_device pdev; /* 0 2208 */ /* --- cacheline 34 boundary (2176 bytes) was 32 bytes ago --- */ - char name[1]; /* 2208 1 */ + char name[0]; /* 2208 0 */ - /* size: 2216, cachelines: 35, members: 2 */ - /* padding: 7 */ - /* last cacheline: 40 bytes */ + /* size: 2208, cachelines: 35, members: 2 */ + /* last cacheline: 32 bytes */ }; --- obj-x86_64/drivers/base/platform.o.pahole.v3.15-rc7-79-gfe45736f4134 = 2014-05-30 10:32:06.432960608 +0200 +++ obj-x86_64/drivers/base/platform.o.pahole.v3.15-rc7-80-g2cdb06858d71 = 2014-05-30 11:26:21.000988250 +0200 @@ -84,9 +84,8 @@ struct platform_object { struct platform_device pdev; /* 0 720 */ /* --- cacheline 11 boundary (704 bytes) was 16 bytes ago --- */ - char name[1]; /* 720 1 */ + char name[0]; /* 720 0 */ - /* size: 728, cachelines: 12, members: 2 */ - /* padding: 7 */ - /* last cacheline: 24 bytes */ + /* size: 720, cachelines: 12, members: 2 */ + /* last cacheline: 16 bytes */ }; Changes from v5 [1]: - dropped dma_mask allocation changes and only kept padding removal changes (name array length set to 0). Changes from v4 [2]: [by Emil Goode :] - Split v4 of the patch into two separate patches. - Generated new object file size and data structure layout info. - Updated the changelog message. Changes from v3 [3]: - fixed commit message so that git am doesn't fail. Changes from v2 [4]: - move 'dma_mask' to platform_object so that it's always allocated and won't leak on release; remove all previously added support functions. - use C99 flexible array member for 'name' to remove padding at the end of platform_object. Changes from v1 [5]: - remove unneeded kfree() from error path - add reference to author/commit adding allocation of dmamask Changes from v0 [6]: - small rewrite to squeeze the patch to a bare minimal [1] http://lkml.kernel.org/r/1401122483-31603-2-git-send-email-emilgoode@gm= ail.com http://lkml.kernel.org/r/1401122483-31603-1-git-send-email-emilgoode@gm= ail.com http://lkml.kernel.org/r/1401122483-31603-3-git-send-email-emilgoode@gm= ail.com [2] http://lkml.kernel.org/r/1390817152-30898-1-git-send-email-ydroneaud@op= teya.com https://patchwork.kernel.org/patch/3541871/ [3] http://lkml.kernel.org/r/1390771138-28348-1-git-send-email-ydroneaud@op= teya.com https://patchwork.kernel.org/patch/3540081/ [4] http://lkml.kernel.org/r/1389683909-17495-1-git-send-email-ydroneaud@op= teya.com https://patchwork.kernel.org/patch/3484411/ [5] http://lkml.kernel.org/r/1389649085-7365-1-git-send-email-ydroneaud@opt= eya.com https://patchwork.kernel.org/patch/3480961/ [6] http://lkml.kernel.org/r/1386886207-2735-1-git-send-email-ydroneaud@opt= eya.com Cc: Emil Goode Cc: Dan Carpenter Cc: Shawn Guo Cc: Sascha Hauer Cc: Russell King Cc: Olof Johansson Cc: Uwe Kleine-K=C3=B6nig Cc: Dmitry Torokhov Cc: Greg Kroah-Hartman Signed-off-by: Yann Droneaud --- drivers/base/platform.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/base/platform.c b/drivers/base/platform.c index 5b47210889e0..b126c9363f53 100644 --- a/drivers/base/platform.c +++ b/drivers/base/platform.c @@ -162,7 +162,7 @@ EXPORT_SYMBOL_GPL(platform_add_devices); =20 struct platform_object { struct platform_device pdev; - char name[1]; + char name[]; }; =20 /** @@ -203,7 +203,7 @@ struct platform_device *platform_device_alloc(const cha= r *name, int id) { struct platform_object *pa; =20 - pa =3D kzalloc(sizeof(struct platform_object) + strlen(name), GFP_KERNEL); + pa =3D kzalloc(sizeof(*pa) + strlen(name) + 1, GFP_KERNEL); if (pa) { strcpy(pa->name, name); pa->pdev.name =3D pa->name; --=20 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html