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Groups > linux.kernel > #1674786
| From | Michael Ellerman <mpe@ellerman.id.au> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3) |
| Date | 2017-06-26 15:40 +0200 |
| Message-ID | <tWCpc-2Xw-27@gated-at.bofh.it> (permalink) |
| References | (6 earlier) <tWcuJ-3q1-7@gated-at.bofh.it> <tWdKa-4oh-9@gated-at.bofh.it> <tWmNs-1oF-21@gated-at.bofh.it> <tWnzP-1VX-3@gated-at.bofh.it> <tWocx-2o4-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Al Viro <viro@ZenIV.linux.org.uk> writes:
> On Sun, Jun 25, 2017 at 04:44:09PM -0500, Segher Boessenkool wrote:
>
>> Do you have a short stand-alone testcase? 4.6 is ancient, of course, but
>> the actual problem may still exist in more recent compilers (if it _is_
>> a compiler problem; if it's not, you *really* want to know :-) )
>
> Enjoy. At least 6.3 doesn't step into that. Look for mtctr in the resulting
> asm...
>
> cat <<'EOF' >a.c
...
I pointed creduce at that and got the version below, which I'm pretty
sure still exhibits the weird mtctr behaviour.
cheers
# cat input.c
struct {
void *iov_base;
unsigned iov_len;
} * c;
long v;
void *a;
int b;
unsigned bar();
foo(unsigned p1) {
unsigned d, e = p1;
if (p1 == 0)
goto out;
if (p1 > 4)
goto out;
if (__builtin_expect(!!(0, v && a), 1))
e = bar();
if (e)
barf(e);
if (e)
goto out;
d = 0;
for (; d < p1; d++) {
int f = c[d].iov_len;
if (__builtin_expect(c[d].iov_base && f, 0))
b = 4;
}
out:;
}
$ cat output.s
.file "input.c"
# rs6000/powerpc options: -mcpu=powerpc -msdata=data -G 8
# GNU C (GCC) version 4.6.3 (powerpc64-linux)
# compiled by GNU C version 4.3.2, GMP version 4.3.2, MPFR version 2.4.2, MPC version 0.8.2
# ...
# Compiler executable checksum: 4b51a6b899110d06c9e3310ac66ad26c
.section ".text"
.align 2
.globl foo
.type foo, @function
foo:
cmpwi 0,3,0 # tmp169, p1
stwu 1,-16(1) #,,
mflr 0 #,
stw 0,20(1) #,
beq- 0,.L9 #
cmplwi 7,3,4 #, tmp170, p1
bgt- 7,.L9 #
lis 9,v@ha # tmp172,
lwz 0,v@l(9) # v, v
cmpwi 7,0,0 #, tmp174, v
beq- 7,.L3 #
lis 9,a@ha # tmp176,
lwz 0,a@l(9) # a, a
cmpwi 7,0,0 #, tmp178, a
beq- 7,.L3 #
bl bar #
cmpwi 0,3,0 # tmp179, e
beq+ 0,.L4 #
.L3:
bl barf #
b .L9 #
.L4:
lis 8,0x2000 #,
lis 9,c@ha # tmp181,
mtctr 8 # tmp192,
lwz 11,c@l(9) # c, c.3
lis 10,b@ha # tmp190,
li 9,0 # ivtmp.12,
li 0,4 # tmp191,
.L6:
lwzx 7,11,9 # MEM[base: c.3_14, index: ivtmp.12_25, offset: 0B], MEM[base: c.3_14, index: ivtmp.12_25, offset: 0B]
add 8,11,9 # tmp182, c.3, ivtmp.12
lwz 8,4(8) # MEM[base: D.1310_21, offset: 4B], D.1287
cmpwi 7,7,0 #, tmp184, MEM[base: c.3_14, index: ivtmp.12_25, offset: 0B]
beq+ 7,.L5 #
cmpwi 7,8,0 #, tmp185, D.1287
beq+ 7,.L5 #
stw 0,b@l(10) # b, tmp191
.L5:
addi 9,9,8 # ivtmp.12, ivtmp.12,
bdnz .L6 #
.L2:
.L9:
lwz 0,20(1) #,
addi 1,1,16 #,,
mtlr 0 #,
blr #
.size foo,.-foo
.globl b
.globl a
.globl v
.globl c
.section .sbss,"aw",@nobits
.align 2
.type b, @object
.size b, 4
b:
.zero 4
.type a, @object
.size a, 4
a:
.zero 4
.type v, @object
.size v, 4
v:
.zero 4
.type c, @object
.size c, 4
c:
.zero 4
.ident "GCC: (GNU) 4.6.3"
.section .note.GNU-stack,"",@progbits
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Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-21 17:20 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-21 23:30 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-21 23:40 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-21 23:50 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-22 16:20 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-22 16:30 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-22 21:30 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-22 23:50 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-23 20:50 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-23 22:40 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Larry Finger <Larry.Finger@lwfinger.net> - 2017-06-24 19:30 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-25 12:00 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-25 13:20 +0200
gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3) Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-25 23:00 +0200
Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3) Segher Boessenkool <segher@kernel.crashing.org> - 2017-06-25 23:50 +0200
Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3) Al Viro <viro@ZenIV.linux.org.uk> - 2017-06-26 00:30 +0200
Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3) Michael Ellerman <mpe@ellerman.id.au> - 2017-06-26 15:40 +0200
Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3 Michael Ellerman <mpe@ellerman.id.au> - 2017-06-26 15:50 +0200
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