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kbuild: avoid unneeded kallsyms step 3

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Since commit 951bcae6c5 ("kallsyms: Avoid weak references for kallsyms
symbols"), the kallsyms step 3 always occurs.

You can compare the build logs.

[Before 951bcae6c5]

  $ git checkout 951bcae6c5a0^
  $ make defconfig all
       [ snip ]
    LD      .tmp_vmlinux.kallsyms1
    NM      .tmp_vmlinux.kallsyms1.syms
    KSYMS   .tmp_vmlinux.kallsyms1.S
    AS      .tmp_vmlinux.kallsyms1.S
    LD      .tmp_vmlinux.kallsyms2
    NM      .tmp_vmlinux.kallsyms2.syms
    KSYMS   .tmp_vmlinux.kallsyms2.S
    AS      .tmp_vmlinux.kallsyms2.S
    LD      vmlinux

[After 951bcae6c5]

  $ git checkout 951bcae6c5
  $ make defconfig all
       [ snip ]
    LD      .tmp_vmlinux.kallsyms1
    NM      .tmp_vmlinux.kallsyms1.syms
    KSYMS   .tmp_vmlinux.kallsyms1.S
    AS      .tmp_vmlinux.kallsyms1.S
    LD      .tmp_vmlinux.kallsyms2
    NM      .tmp_vmlinux.kallsyms2.syms
    KSYMS   .tmp_vmlinux.kallsyms2.S
    AS      .tmp_vmlinux.kallsyms2.S
    LD      .tmp_vmlinux.kallsyms3             # should not happen
    NM      .tmp_vmlinux.kallsyms3.syms        # should not happen
    KSYMS   .tmp_vmlinux.kallsyms3.S           # should not happen
    AS      .tmp_vmlinux.kallsyms3.S           # should not happen
    LD      vmlinux

The resulting vmlinux is correct, but it always requires an additional
linking step.

The symbols produced by kallsyms are excluded from kallsyms itself
because they were previously missing in step 1. With those symbols
excluded, the symbol lists matched between step 1 and step 2,
eliminating the need for step 3. Now, this has a negative effect.

Since 951bcae6c5, the PROVIDE() directives provide the fallback
definitions, which are not trimmed from the sysbol list in step 1
because ${kallsymso_prev} is empty at this point.

In step 2, ${kallsymso_prev} is set, and the kallsyms_* symbols are
trimmed from the symbol list.

Due to the table size difference between step 1 and step 2 (the former
is larger due to the presence of kallsyms_*), step 3 is triggered.

Now that the kallsyms_* symbols are always linked, let's stop omitting
them from kallsyms. This avoids unnecessary step 3.

Fixes: 951bcae6c5 ("kallsyms: Avoid weak references for kallsyms symbols")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Masahiro Yamada 2024-05-20 21:42:09 +09:00
parent 659bbf7e1b
commit 04b8cb0945
2 changed files with 4 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
scripts/link-vmlinux.sh
View File

@ -179,7 +179,7 @@ kallsyms_step()
kallsyms_S=${kallsyms_vmlinux}.S
vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o}
mksysmap ${kallsyms_vmlinux} ${kallsyms_vmlinux}.syms ${kallsymso_prev}
mksysmap ${kallsyms_vmlinux} ${kallsyms_vmlinux}.syms
kallsyms ${kallsyms_vmlinux}.syms ${kallsyms_S}
info AS ${kallsyms_S}
@ -193,7 +193,7 @@ kallsyms_step()
mksysmap()
{
info NM ${2}
${CONFIG_SHELL} "${srctree}/scripts/mksysmap" ${1} ${2} ${3}
${CONFIG_SHELL} "${srctree}/scripts/mksysmap" ${1} ${2}
}
sorttable()
@ -282,7 +282,7 @@ if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
${RESOLVE_BTFIDS} vmlinux
fi
mksysmap vmlinux System.map ${kallsymso}
mksysmap vmlinux System.map
if is_enabled CONFIG_BUILDTIME_TABLE_SORT; then
info SORTTAB vmlinux

11
scripts/mksysmap
View File

@ -4,7 +4,7 @@
# tools to retrieve the actual addresses of symbols in the kernel.
#
# Usage
# mksysmap vmlinux System.map [exclude]
# mksysmap vmlinux System.map
#####
@ -92,13 +92,4 @@ ${NM} -n ${1} | sed >${2} -e "
# ppc stub
/\.long_branch\./d
/\.plt_branch\./d
# ---------------------------------------------------------------------------
# Ignored kallsyms symbols
#
# If the 3rd parameter exists, symbols from it will be omitted from the output.
# This makes kallsyms have the identical symbol lists in the step 1 and 2.
# Without this, the step2 would get new symbols generated by scripts/kallsyms.c
# when CONFIG_KALLSYMS_ALL is enabled. That might require one more pass.
$(if [ $# -ge 3 ]; then ${NM} ${3} | sed -n '/ U /!s:.* \([^ ]*\)$:/ \1$/d:p'; fi)
"