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kbuild: link-vmlinux.sh: improve detection of third pass requirement

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It can happen that symbol sizes within .tmp_vmlinux1.kallsyms.o and
.tmp_vmlinux2.kallsyms.o differ, without affecting file size on disk
because of section alignment and/or padding emitted by the assembler.

link-vmlinux.sh doesn't detect this case currently and keeps using
.tmp_vmlinux2.kallsyms.o to link the final vmlinux. Due to the
different symbol sizes, other symbols are shifted within the final
image compared to .tmp_vmlinux2, and the final comparison of System.map
against "${kallsyms_sysmap}" fails with the message:

    Inconsistent kallsyms data
    Try "make KALLSYMS_EXTRA_PASS=1" as a workaround

This can happen in particular if the linker emits additional symbols
that might have different names between our (re-)linking steps, e.g.
because those names depend on the virtual address of the symbol. Linker
stubs for ARM errata work-arounds are one such case.

These changed symbol names can cause the output of the token
compression of kallsyms.c to change due to the changed symbol substring
count, which in turn can change the size of the kallsyms_names symbol
itself, causing the potential shift of subsequent symbol addresses in
.tmp_vmlinux2.kallsyms.o and therefore the final image.

Update link-vmlinux.sh to not rely on file size of
.tmp_vmlinux?.kallsyms.o alone but to also consider symbol offsets
within to resolve this, and do a third pass if required.

Signed-off-by: André Draszik <andre.draszik@linaro.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Signed-off-by: Nicolas Schier <nsc@kernel.org>
This commit is contained in:
André Draszik
2026-07-28 13:42:40 +01:00
committed by Nicolas Schier
parent d6bf11a7e8
commit 14b8b4bf2d
1 changed files with 19 additions and 1 deletions
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20
scripts/link-vmlinux.sh
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@@ -106,6 +106,18 @@ vmlinux_link()
${kallsymso} ${btf_vmlinux_bin_o} ${arch_vmlinux_o} ${ldlibs}
}
# Check if kallsymso_prev and kallsymso differ
# If symbol sizes within ${kallsymso} change, any symbols within vmlinux are
# likely to shift, invalidating ${kallsymso}.
# Since file size can remain unchanged even if symbol sizes change, compare the
# actual symbols instead of relying on file size only.
kallsymso_changed()
{
${NM} -n "${kallsymso_prev}" > "${kallsymso_prev}.sym"
${NM} -n "${kallsymso}" > "${kallsymso}.sym"
! cmp -s "${kallsymso_prev}.sym" "${kallsymso}.sym"
}
# Create ${2}.o file with all symbols from the ${1} object file
kallsyms()
{
@@ -126,6 +138,7 @@ kallsyms()
${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} -c -o "${2}.o" "${2}.S"
kallsymso_prev="${kallsymso:-}"
kallsymso=${2}.o
}
@@ -255,7 +268,12 @@ if is_enabled CONFIG_KALLSYMS; then
sysmap_and_kallsyms .tmp_vmlinux2
size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
# Due to alignment, file size of the kallsymso object file might remain
# unchanged even if individual symbols within change size. Changed
# symbol sizes can still shift other symbols, though. Therefore, don't
# rely on file size alone.
if [ $size1 -ne $size2 ] || kallsymso_changed || \
[ -n "${KALLSYMS_EXTRA_PASS}" ]; then
vmlinux_link .tmp_vmlinux3
sysmap_and_kallsyms .tmp_vmlinux3
fi