334710b149
unsafe_put_user() is designed to take benefit of 'asm goto'.
Instead of using the standard __put_user() approach and branch
based on the returned error, use 'asm goto' and make the
exception code branch directly to the error label. There is
no code anymore in the fixup section.
This change significantly simplifies functions using
unsafe_put_user()
Small exemple of the benefit with the following code:
struct test {
u32 item1;
u16 item2;
u8 item3;
u64 item4;
};
int set_test_to_user(struct test __user *test, u32 item1, u16 item2, u8 item3, u64 item4)
{
unsafe_put_user(item1, &test->item1, failed);
unsafe_put_user(item2, &test->item2, failed);
unsafe_put_user(item3, &test->item3, failed);
unsafe_put_user(item4, &test->item4, failed);
return 0;
failed:
return -EFAULT;
}
Before the patch:
00000be8 <set_test_to_user>:
be8: 39 20 00 00 li r9,0
bec: 90 83 00 00 stw r4,0(r3)
bf0: 2f 89 00 00 cmpwi cr7,r9,0
bf4: 40 9e 00 38 bne cr7,c2c <set_test_to_user+0x44>
bf8: b0 a3 00 04 sth r5,4(r3)
bfc: 2f 89 00 00 cmpwi cr7,r9,0
c00: 40 9e 00 2c bne cr7,c2c <set_test_to_user+0x44>
c04: 98 c3 00 06 stb r6,6(r3)
c08: 2f 89 00 00 cmpwi cr7,r9,0
c0c: 40 9e 00 20 bne cr7,c2c <set_test_to_user+0x44>
c10: 90 e3 00 08 stw r7,8(r3)
c14: 91 03 00 0c stw r8,12(r3)
c18: 21 29 00 00 subfic r9,r9,0
c1c: 7d 29 49 10 subfe r9,r9,r9
c20: 38 60 ff f2 li r3,-14
c24: 7d 23 18 38 and r3,r9,r3
c28: 4e 80 00 20 blr
c2c: 38 60 ff f2 li r3,-14
c30: 4e 80 00 20 blr
00000000 <.fixup>:
...
b8: 39 20 ff f2 li r9,-14
bc: 48 00 00 00 b bc <.fixup+0xbc>
bc: R_PPC_REL24 .text+0xbf0
c0: 39 20 ff f2 li r9,-14
c4: 48 00 00 00 b c4 <.fixup+0xc4>
c4: R_PPC_REL24 .text+0xbfc
c8: 39 20 ff f2 li r9,-14
cc: 48 00 00 00 b cc <.fixup+0xcc>
d0: 39 20 ff f2 li r9,-14
d4: 48 00 00 00 b d4 <.fixup+0xd4>
d4: R_PPC_REL24 .text+0xc18
00000000 <__ex_table>:
...
a0: R_PPC_REL32 .text+0xbec
a4: R_PPC_REL32 .fixup+0xb8
a8: R_PPC_REL32 .text+0xbf8
ac: R_PPC_REL32 .fixup+0xc0
b0: R_PPC_REL32 .text+0xc04
b4: R_PPC_REL32 .fixup+0xc8
b8: R_PPC_REL32 .text+0xc10
bc: R_PPC_REL32 .fixup+0xd0
c0: R_PPC_REL32 .text+0xc14
c4: R_PPC_REL32 .fixup+0xd0
After the patch:
00000be8 <set_test_to_user>:
be8: 90 83 00 00 stw r4,0(r3)
bec: b0 a3 00 04 sth r5,4(r3)
bf0: 98 c3 00 06 stb r6,6(r3)
bf4: 90 e3 00 08 stw r7,8(r3)
bf8: 91 03 00 0c stw r8,12(r3)
bfc: 38 60 00 00 li r3,0
c00: 4e 80 00 20 blr
c04: 38 60 ff f2 li r3,-14
c08: 4e 80 00 20 blr
00000000 <__ex_table>:
...
a0: R_PPC_REL32 .text+0xbe8
a4: R_PPC_REL32 .text+0xc04
a8: R_PPC_REL32 .text+0xbec
ac: R_PPC_REL32 .text+0xc04
b0: R_PPC_REL32 .text+0xbf0
b4: R_PPC_REL32 .text+0xc04
b8: R_PPC_REL32 .text+0xbf4
bc: R_PPC_REL32 .text+0xc04
c0: R_PPC_REL32 .text+0xbf8
c4: R_PPC_REL32 .text+0xc04
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/23e680624680a9a5405f4b88740d2596d4b17c26.1587143308.git.christophe.leroy@c-s.fr
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.