Messages in this thread Patches in this message | | | From | Christophe Leroy <> | Subject | Re: [RFC PATCH v3 11/12] powerpc: Remove unreachable() from WARN_ON() | Date | Wed, 29 Jun 2022 18:30:23 +0000 |
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Hi Sathvika,
Adding ARM people as they seem to face the same kind of problem (see https://patchwork.kernel.org/project/linux-kbuild/patch/20220623014917.199563-33-chenzhongjin@huawei.com/)
Le 27/06/2022 à 17:35, Sathvika Vasireddy a écrit : > > On 25/06/22 12:16, Christophe Leroy wrote: >> >> Le 24/06/2022 à 20:32, Sathvika Vasireddy a écrit : >>> objtool is throwing *unannotated intra-function call* >>> warnings with a few instructions that are marked >>> unreachable. Remove unreachable() from WARN_ON() >>> to fix these warnings, as the codegen remains same >>> with and without unreachable() in WARN_ON(). >> Did you try the two exemples described in commit 1e688dd2a3d6 >> ("powerpc/bug: Provide better flexibility to WARN_ON/__WARN_FLAGS() with >> asm goto") ? >> >> Without your patch: >> >> 00000640 <test>: >> 640: 81 23 00 84 lwz r9,132(r3) >> 644: 71 29 40 00 andi. r9,r9,16384 >> 648: 40 82 00 0c bne 654 <test+0x14> >> 64c: 80 63 00 0c lwz r3,12(r3) >> 650: 4e 80 00 20 blr >> 654: 0f e0 00 00 twui r0,0 >> >> 00000658 <test9w>: >> 658: 2c 04 00 00 cmpwi r4,0 >> 65c: 41 82 00 0c beq 668 <test9w+0x10> >> 660: 7c 63 23 96 divwu r3,r3,r4 >> 664: 4e 80 00 20 blr >> 668: 0f e0 00 00 twui r0,0 >> 66c: 38 60 00 00 li r3,0 >> 670: 4e 80 00 20 blr >> >> >> With your patch: >> >> 00000640 <test>: >> 640: 81 23 00 84 lwz r9,132(r3) >> 644: 71 29 40 00 andi. r9,r9,16384 >> 648: 40 82 00 0c bne 654 <test+0x14> >> 64c: 80 63 00 0c lwz r3,12(r3) >> 650: 4e 80 00 20 blr >> 654: 0f e0 00 00 twui r0,0 >> 658: 4b ff ff f4 b 64c <test+0xc> <== >> >> 0000065c <test9w>: >> 65c: 2c 04 00 00 cmpwi r4,0 >> 660: 41 82 00 0c beq 66c <test9w+0x10> >> 664: 7c 63 23 96 divwu r3,r3,r4 >> 668: 4e 80 00 20 blr >> 66c: 0f e0 00 00 twui r0,0 >> 670: 38 60 00 00 li r3,0 <== >> 674: 4e 80 00 20 blr <== >> 678: 38 60 00 00 li r3,0 >> 67c: 4e 80 00 20 blr >> > The builtin variant of unreachable (__builtin_unreachable()) works. > > How about using that instead of unreachable() ? > >
In fact the problem comes from the macro annotate_unreachable() which is called by unreachable() before calling __build_unreachable().
Seems like this macro adds (after the unconditional trap twui) a call to an empty function whose address is listed in section .discard.unreachable
1c78: 00 00 e0 0f twui r0,0 1c7c: 55 e7 ff 4b bl 3d0 <qdisc_root_sleeping_lock.part.0>
RELOCATION RECORDS FOR [.discard.unreachable]: OFFSET TYPE VALUE 0000000000000000 R_PPC64_REL32 .text+0x00000000000003d0
The problem is that that function has size 0:
00000000000003d0 l F .text 0000000000000000 qdisc_root_sleeping_lock.part.0
And objtool is not prepared for a function with size 0.
The following changes to objtool seem to fix the problem, most warning are gone with that change.
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 63218f5799c2..37c0a268b7ea 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -77,6 +77,8 @@ static int symbol_by_offset(const void *key, const struct rb_node *node)
if (*o < s->offset) return -1; + if (*o == s->offset && !s->len) + return 0; if (*o >= s->offset + s->len) return 1;
@@ -400,7 +402,7 @@ static void elf_add_symbol(struct elf *elf, struct symbol *sym) * Don't store empty STT_NOTYPE symbols in the rbtree. They * can exist within a function, confusing the sorting. */ - if (!sym->len) + if (sym->type == STT_NOTYPE && !sym->len) rb_erase(&sym->node, &sym->sec->symbol_tree); }
--- I also had objtool running for ever on arch/powerpc/sysdev/xics/icp-hv.o, which I fixed with the below hack:
diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 51b6dcec8d6a..ef2303ad6381 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -529,7 +529,7 @@ static struct instruction *find_last_insn(struct objtool_file *file, unsigned int offset; unsigned int end = (sec->sh.sh_size > 10) ? sec->sh.sh_size - 10 : 0;
- for (offset = sec->sh.sh_size - 1; offset >= end && !insn; offset--) + for (offset = sec->sh.sh_size - 1; offset && offset >= end && !insn; offset--) insn = find_insn(file, sec, offset);
return insn; ---
Now I only have the following two warnings:
arch/powerpc/sysdev/xics/icp-hv.o: warning: objtool: can't find unreachable insn at .text.unlikely+0x0 drivers/crypto/vmx/aesp8-ppc.o: warning: objtool: aes_p8_set_encrypt_key+0x44: unannotated intra-function call
The first one is linked to the infinite loop I hacked. So I now have to understand what the problem really is.
The second one is an assembly file aesp8-ppc.S which lacks the changes you did in other assembly files in patch 12.
Christophe | |