Le 26/04/2021 à 20:50, Nathan Chancellor a écrit :
On Sat, Mar 20, 2021 at 11:22:27PM +1100, Michael Ellerman wrote:
From: Christophe Leroy <christophe.le...@csgroup.eu>
call_do_irq() and call_do_softirq() are simple enough to be
worth inlining.
Inlining them avoids an mflr/mtlr pair plus a save/reload on stack. It
also allows GCC to keep the saved ksp_limit in an nonvolatile reg.
This is inspired from S390 arch. Several other arches do more or
less the same. The way sparc arch does seems odd thought.
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
This change caused our ppc44x_defconfig builds to hang when powering
down in QEMU:
https://github.com/ClangBuiltLinux/continuous-integration2/runs/2304364629?check_suite_focus=true#logs
This is probably something with clang given that GCC 10.3.0 works fine
but due to the nature of the change, I have no idea how to tell what is
going wrong. I tried to do some rudimentary debugging with gdb but that
did not really get me anywhere.
The kernel was built with just 'CC=clang' and it is reproducible with
all versions of clang that the kernel supports.
The QEMU invocation is visible at the link above, it is done with our
boot-qemu.sh in this repo, which also houses the rootfs:
https://github.com/ClangBuiltLinux/boot-utils
Happy to provide any other information or debug/test as directed!
With GCC:
000003f0 <do_softirq_own_stack>:
3f0: 94 21 ff f0 stwu r1,-16(r1)
3f4: 7c 08 02 a6 mflr r0
3f8: 3d 20 00 00 lis r9,0
3fa: R_PPC_ADDR16_HA .data..read_mostly+0x4
3fc: 93 e1 00 0c stw r31,12(r1)
400: 90 01 00 14 stw r0,20(r1)
404: 83 e9 00 00 lwz r31,0(r9)
406: R_PPC_ADDR16_LO .data..read_mostly+0x4
408: 94 3f 1f f0 stwu r1,8176(r31)
40c: 7f e1 fb 78 mr r1,r31
410: 48 00 00 01 bl 410 <do_softirq_own_stack+0x20>
410: R_PPC_REL24 __do_softirq
414: 80 21 00 00 lwz r1,0(r1)
418: 80 01 00 14 lwz r0,20(r1)
41c: 83 e1 00 0c lwz r31,12(r1)
420: 38 21 00 10 addi r1,r1,16
424: 7c 08 03 a6 mtlr r0
428: 4e 80 00 20 blr
With CLANG:
000003e8 <do_softirq_own_stack>:
3e8: 94 21 ff f0 stwu r1,-16(r1)
3ec: 93 c1 00 08 stw r30,8(r1)
3f0: 3c 60 00 00 lis r3,0
3f2: R_PPC_ADDR16_HA softirq_ctx
3f4: 83 c3 00 00 lwz r30,0(r3)
3f6: R_PPC_ADDR16_LO softirq_ctx
3f8: 94 3e 1f f0 stwu r1,8176(r30)
3fc: 7f c1 f3 78 mr r1,r30
400: 48 00 00 01 bl 400 <do_softirq_own_stack+0x18>
400: R_PPC_REL24 __do_softirq
404: 80 21 00 00 lwz r1,0(r1)
408: 83 c1 00 08 lwz r30,8(r1)
40c: 38 21 00 10 addi r1,r1,16
410: 4e 80 00 20 blr
As you can see, CLANG doesn't save/restore 'lr' allthought 'lr' is explicitely listed in the
registers clobbered by the inline assembly:
>> +static __always_inline void call_do_softirq(const void *sp)
>> +{
>> + /* Temporarily switch r1 to sp, call __do_softirq() then restore r1.
*/
>> + asm volatile (
>> + PPC_STLU " %%r1, %[offset](%[sp]) ;"
>> + "mr %%r1, %[sp] ;"
>> + "bl %[callee] ;"
>> + PPC_LL " %%r1, 0(%%r1) ;"
>> + : // Outputs
>> + : // Inputs
>> + [sp] "b" (sp), [offset] "i" (THREAD_SIZE -
STACK_FRAME_OVERHEAD),
>> + [callee] "i" (__do_softirq)
>> + : // Clobbers
>> + "lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6",
>> + "cr7", "r0", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
"r10",
>> + "r11", "r12"
>> + );
