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kpatch-build error: can't create dynrela for section .rela.static_call_sites  #1272

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#1273
Closed
kpatch-build error: can't create dynrela for section .rela.static_call_sites #1272
#1273

Description

@liu-song-6
liu-song-6
opened on Jun 6, 2022

We are seeing the following error from kpatch-build

space-info.o: changed function: __reserve_bytes
/data/users/songliubraving/kpatch/kpatch-build/create-diff-object: ERROR: space-info.o: kpatch_create_intermediate_sections: 3362: can't create dynrela for section .rela.static_call_sites (symbol __SCK__tp_func_btrfs_done_preemptive_reclaim): no bundled or section symbol

The patch to repro this error can be very simple:

diff --git i/fs/btrfs/space-info.c w/fs/btrfs/space-info.c
index e692c880deb7..ae7497b430e9 100644
--- i/fs/btrfs/space-info.c
+++ w/fs/btrfs/space-info.c
@@ -1489,6 +1489,8 @@ static int __reserve_bytes(struct btrfs_fs_info *fs_info,
        int ret = 0;
        bool pending_tickets;

+       if (IS_ERR(fs_info))
+               return 0;
        ASSERT(orig_bytes);
        ASSERT(!current->journal_info || flush != BTRFS_RESERVE_FLUSH_ALL);

After digging into this, we found this happens because missing symbol name for the .static_call_sites section. We need to access static_call_sites section for the tracepoint call trace_btrfs_done_preemptive_reclaim. The symbol name for static_call_sites is generated by the following step in scripts/Makefile.build:

cmd_modversions_c =                                                             \
        if $(OBJDUMP) -h $@ | grep -q __ksymtab; then                           \
                $(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))  \
                    > $(@D)/.tmp_$(@F:.o=.ver);                                 \
                                                                                \
                $(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@               \
                        -T $(@D)/.tmp_$(@F:.o=.ver);                            \
                mv -f $(@D)/.tmp_$(@F) $@;                                      \
                rm -f $(@D)/.tmp_$(@F:.o=.ver);                                 \
        fi
endif

As space-info.c doesn't export any symbol, space-info.o doesn't have any __ksymtab, and we skipped cmd_gensymtypes_c.

I tried a few things to fix this issue, but haven't figured out a good solution. Any suggestions on what would be the best fix here?

Thanks!

Activity

  1. jpoimboe commented on Jun 6, 2022

    @jpoimboe
    jpoimboe
    on Jun 6, 2022
    Member

    Recent toolchains only create a section symbol if it's needed, i.e. if there's a reference to it. I think the fix here would be to just create the section symbol, something like so (untested)

    diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index bebe3bd..d71259b 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -3355,12 +3355,23 @@ static void kpatch_create_intermediate_sections(struct kpatch_elf *kelf,
 
 			/* add rela to fill in krelas[index].dest field */
 			ALLOC_LINK(rela2, &krela_sec->rela->relas);
-			if (relasec->base->secsym)
-				rela2->sym = relasec->base->secsym;
-			else
-				ERROR("can't create dynrela for section %s (symbol %s): no bundled or section symbol",
-				      relasec->name, rela->sym->name);
+			if (!relasec->base->secsym) {
+				struct symbol *sym;
 
+				/*
+				 * Newer toolchains are stingy with their
+				 * section symbols, create one if it doesn't
+				 * exist already.
+				 */
+				ALLOC_LINK(sym, &kelf->symbols);
+				sym->sec = relasec->base;
+				sym->sym.st_info = GELF_ST_INFO(STB_LOCAL, STT_SECTION);
+				sym->type = STT_SECTION;
+				sym->bind = STB_LOCAL;
+				sym->name = relasec->base->name;
+				relasec->base->secsym = sym;
+			}
+			rela2->sym = relasec->base->secsym;
 			rela2->type = absolute_rela_type(kelf);
 			rela2->addend = rela->offset;
 			rela2->offset = (unsigned int)(index * sizeof(*krelas) + \

  2. jpoimboe commented on Jun 7, 2022

    @jpoimboe
    jpoimboe
    on Jun 7, 2022
    Member

    I was able to recreate, and I verified the above patch fixed it. Will make a pull request.

  3. jpoimboe
    added a commit that references this issue on Jun 7, 2022

    create-diff-object: Create missing section symbol

    9c0709f

  4. liu-song-6 commented on Jun 7, 2022

    @liu-song-6
    liu-song-6
    on Jun 7, 2022
    ContributorAuthor

    Yes, this works great, thanks!

  5. liu-song-6
    added a commit that references this issue on Jun 7, 2022

    create-diff-object: Create missing section symbol

    3112397
  6. jpoimboe
    added a commit that references this issue on Jun 8, 2022

    create-diff-object: Create missing section symbol

    a1171b1
  7. jpoimboe
    closed this as completedin #1273on Jun 8, 2022
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