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Using asm goto in __WARN_FLAGS() and WARN_ON() allows more
flexibility to GCC.
For that add an entry to the exception table so that
program_check_exception() knowns where to resume execution
after a WARNING.
Here are two exemples. The first one is done on PPC32 (which
benefits from the previous patch), the second is on PPC64.
unsigned long test(struct pt_regs *regs)
{
int ret;
WARN_ON(regs->msr & MSR_PR);
return regs->gpr[3];
}
unsigned long test9w(unsigned long a, unsigned long b)
{
if (WARN_ON(!b))
return 0;
return a / b;
}
Before the patch:
000003a8 <test>:
3a8: 81 23 00 84 lwz r9,132(r3)
3ac: 71 29 40 00 andi. r9,r9,16384
3b0: 40 82 00 0c bne 3bc <test+0x14>
3b4: 80 63 00 0c lwz r3,12(r3)
3b8: 4e 80 00 20 blr
3bc: 0f e0 00 00 twui r0,0
3c0: 80 63 00 0c lwz r3,12(r3)
3c4: 4e 80 00 20 blr
0000000000000bf0 <.test9w>:
bf0: 7c 89 00 74 cntlzd r9,r4
bf4: 79 29 d1 82 rldicl r9,r9,58,6
bf8: 0b 09 00 00 tdnei r9,0
bfc: 2c 24 00 00 cmpdi r4,0
c00: 41 82 00 0c beq c0c <.test9w+0x1c>
c04: 7c 63 23 92 divdu r3,r3,r4
c08: 4e 80 00 20 blr
c0c: 38 60 00 00 li r3,0
c10: 4e 80 00 20 blr
After the patch:
000003a8 <test>:
3a8: 81 23 00 84 lwz r9,132(r3)
3ac: 71 29 40 00 andi. r9,r9,16384
3b0: 40 82 00 0c bne 3bc <test+0x14>
3b4: 80 63 00 0c lwz r3,12(r3)
3b8: 4e 80 00 20 blr
3bc: 0f e0 00 00 twui r0,0
0000000000000c50 <.test9w>:
c50: 7c 89 00 74 cntlzd r9,r4
c54: 79 29 d1 82 rldicl r9,r9,58,6
c58: 0b 09 00 00 tdnei r9,0
c5c: 7c 63 23 92 divdu r3,r3,r4
c60: 4e 80 00 20 blr
c70: 38 60 00 00 li r3,0
c74: 4e 80 00 20 blr
In the first exemple, we see GCC doesn't need to duplicate what
happens after the trap.
In the second exemple, we see that GCC doesn't need to emit a test
and a branch in the likely path in addition to the trap.
We've got some WARN_ON() in .softirqentry.text section so it needs
to be added in the OTHER_TEXT_SECTIONS in modpost.c
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/389962b1b702e3c78d169e59bcfac56282889173.1618331882.git.christophe.leroy@csgroup.eu
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.