Re: util-linux-2.41 breaks static build of btrfs-progs

On Mon, May 05, 2025 at 11:34:11AM +0200, Karel Zak wrote:
> On Sun, Apr 20, 2025 at 09:24:43PM +0200, Stanislav Brabec wrote:
> > Static build of btrfs-progs fails with util-linux-2.41 with a simple
> > problem:
> > Symbol parse_range becomes visible in libblkid.a, breaking parse-utils.c in
> > btrfs-progs, using the same symbol.
> > 
> > The question is:
> > Should be this fixed by util-linux by prefixing of ul_ to all symbols that
> > are not declared as static?
> 
> I think the ul_ prefix should be used for all generic names like
> parse_range(). I'm not sure if I want to use it strictly for all
> functions, as the set of functions is large and such conflicts are
> very rare.
> 
> ChatGPT has an interesting suggestion: add the prefix to the .a
> library using "objcopy --redefine-syms" for all non-API and non-static
> functions.
> 
>         #!/bin/bash
>         PREFIX=foo_
> 
>         # Extract all global (non-static) function symbols from the .a file
>         nm -g --defined-only libmylib.a | awk '{print $3}' | grep -v "^$PREFIX" | sort -u > tmp.syms

Note that the list of symbols should also be filtered according to
libblkid.sym to keep the API functions unmodified.

>         # Generate rename list: <old> <new>
>         awk -v pfx="$PREFIX" '{print $1 " " pfx $1}' tmp.syms > rename.syms
> 
>         # Apply symbol renaming
>         objcopy --redefine-syms=rename.syms libmylib.a libmylib_prefixed.a


Updated, not tested version:

#!/bin/bash

set -e

LIB=libfoo.a
VERSION_SCRIPT=libfoo.sym
PREFIX=foo_
TMPDIR=$(mktemp -d)
RENAME_SYMS="$TMPDIR/rename.syms"

# 1. Get all defined global symbols in the .a (non-static functions/vars)
nm -g --defined-only "$LIB" | awk '{print $3}' | sort -u > "$TMPDIR/all_syms.txt"

# 2. Extract exported (API) symbols from the version script
awk '/global:/{flag=1; next} /local:/{flag=0} flag' "$VERSION_SCRIPT" | \
    tr -d '; \t' | grep -v '^$' | sort -u > "$TMPDIR/exported_syms.txt"

# 3. Compute symbols to rename (non-exported global ones)
comm -23 "$TMPDIR/all_syms.txt" "$TMPDIR/exported_syms.txt" | \
    awk -v pfx="$PREFIX" '{print $1 " " pfx $1}' > "$RENAME_SYMS"

# 4. Apply renaming to the archive
cp "$LIB" "${LIB%.a}_prefixed.a"
objcopy --redefine-syms="$RENAME_SYMS" "${LIB%.a}_prefixed.a"

echo "Renamed library created: ${LIB%.a}_prefixed.a"
echo "Renamed symbols:"
cat "$RENAME_SYMS"

# 5. Optional cleanup
# rm -r "$TMPDIR"



-- 
 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com