On 02/11/2013 07:33 PM, Linus Torvalds wrote: > On Mon, Feb 11, 2013 at 5:37 PM, tip-bot for H. Peter Anvin > <hpa@xxxxxxxxx> wrote: >> >> However, we can declare a bitfield using sizeof(), which is legal >> because sizeof() is a constant expression. This quiets the warning, >> although the code generated isn't 100% identical from the baseline >> before 96477b4 x86-32: Add support for 64bit get_user(): > > Christ. This is so ugly that it's almost a work of art. :) > Has anybody run this past any gcc developers? And if so, did they run > away screaming? I haven't no... H.J., any comments on this patch? -hpa
--- Begin Message ---
- Subject: [tip:x86/mm] x86, mm: Use a bitfield to mask nuisance get_user() warnings
- From: "tip-bot for H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Mon, 11 Feb 2013 17:37:52 -0800
- Cc: linux-kernel@xxxxxxxxxxxxxxx, hpa@xxxxxxxxx, mingo@xxxxxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx, jamie@xxxxxxxxxxxxx, ville.syrjala@xxxxxxxxxxxxxxx, bp@xxxxxxxxx, linux@xxxxxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx
- Git-commit-id: b390784dc1649f6e6c5e66e5f53c21e715ccf39b
- In-reply-to: <20130209110031.GA17833@n2100.arm.linux.org.uk>
- Reply-to: mingo@xxxxxxxxxx, hpa@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, jamie@xxxxxxxxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx, ville.syrjala@xxxxxxxxxxxxxxx, bp@xxxxxxxxx, linux@xxxxxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx
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Commit-ID: b390784dc1649f6e6c5e66e5f53c21e715ccf39b Gitweb: http://git.kernel.org/tip/b390784dc1649f6e6c5e66e5f53c21e715ccf39b Author: H. Peter Anvin <hpa@xxxxxxxxx> AuthorDate: Mon, 11 Feb 2013 16:27:28 -0800 Committer: H. Peter Anvin <hpa@xxxxxxxxx> CommitDate: Mon, 11 Feb 2013 17:26:51 -0800 x86, mm: Use a bitfield to mask nuisance get_user() warnings Even though it is never executed, gcc wants to warn for casting from a large integer to a pointer. Furthermore, using a variable with __typeof__() doesn't work because __typeof__ retains storage specifiers (const, restrict, volatile). However, we can declare a bitfield using sizeof(), which is legal because sizeof() is a constant expression. This quiets the warning, although the code generated isn't 100% identical from the baseline before 96477b4 x86-32: Add support for 64bit get_user(): [x86-mb is baseline, x86-mm is this commit] text data bss filename 113716147 15858380 35037184 tip.x86-mb/o.i386-allconfig/vmlinux 113716145 15858380 35037184 tip.x86-mm/o.i386-allconfig/vmlinux 12989837 3597944 12255232 tip.x86-mb/o.i386-modconfig/vmlinux 12989831 3597944 12255232 tip.x86-mm/o.i386-modconfig/vmlinux 1462784 237608 1401988 tip.x86-mb/o.i386-noconfig/vmlinux 1462837 237608 1401964 tip.x86-mm/o.i386-noconfig/vmlinux 7938994 553688 7639040 tip.x86-mb/o.i386-pae/vmlinux 7943136 557784 7639040 tip.x86-mm/o.i386-pae/vmlinux 7186126 510572 6574080 tip.x86-mb/o.i386/vmlinux 7186124 510572 6574080 tip.x86-mm/o.i386/vmlinux 103747269 33578856 65888256 tip.x86-mb/o.x86_64-allconfig/vmlinux 103746949 33578856 65888256 tip.x86-mm/o.x86_64-allconfig/vmlinux 12116695 11035832 20160512 tip.x86-mb/o.x86_64-modconfig/vmlinux 12116567 11035832 20160512 tip.x86-mm/o.x86_64-modconfig/vmlinux 1700790 380524 511808 tip.x86-mb/o.x86_64-noconfig/vmlinux 1700790 380524 511808 tip.x86-mm/o.x86_64-noconfig/vmlinux 12413612 1133376 1101824 tip.x86-mb/o.x86_64/vmlinux 12413484 1133376 1101824 tip.x86-mm/o.x86_64/vmlinux Cc: Jamie Lokier <jamie@xxxxxxxxxxxxx> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/20130209110031.GA17833@xxxxxxxxxxxxxxxxxxxxxx Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx> --- arch/x86/include/asm/uaccess.h | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 1e96326..a8d1265 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -168,31 +168,29 @@ do { \ #define get_user(x, ptr) \ ({ \ int __ret_gu; \ - unsigned long __val_gu; \ - unsigned long long __val_gu8; \ + struct { \ + unsigned long long __val_n : 8*sizeof(*(ptr)); \ + } __val_gu; \ __chk_user_ptr(ptr); \ might_fault(); \ switch (sizeof(*(ptr))) { \ case 1: \ - __get_user_x(1, __ret_gu, __val_gu, ptr); \ + __get_user_x(1, __ret_gu, __val_gu.__val_n, ptr); \ break; \ case 2: \ - __get_user_x(2, __ret_gu, __val_gu, ptr); \ + __get_user_x(2, __ret_gu, __val_gu.__val_n, ptr); \ break; \ case 4: \ - __get_user_x(4, __ret_gu, __val_gu, ptr); \ + __get_user_x(4, __ret_gu, __val_gu.__val_n, ptr); \ break; \ case 8: \ - __get_user_8(__ret_gu, __val_gu8, ptr); \ + __get_user_8(__ret_gu, __val_gu.__val_n, ptr); \ break; \ default: \ - __get_user_x(X, __ret_gu, __val_gu, ptr); \ + __get_user_x(X, __ret_gu, __val_gu.__val_n, ptr); \ break; \ } \ - if (sizeof(*(ptr)) == 8) \ - (x) = (__typeof__(*(ptr)))__val_gu8; \ - else \ - (x) = (__typeof__(*(ptr)))__val_gu; \ + (x) = (__typeof__(*(ptr)))__val_gu.__val_n; \ __ret_gu; \ })
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