GifQuantizeBuffer function is not defined in libgif.so in giflib-5.1.9, but is still declared in installed gif_lib.h header and is still used by some other software (e.g. mplayer).
Original bug: https://bugs.gentoo.org/682198
Full comparison of lists of defined symbols between giflib-5.1.8 and giflib-5.1.9:
# diff -u <(nm -C -D --defined-only --with-symbol-versions giflib-5.1.8-r1/image/usr/lib64/libgif.so | sed -e "s/^[0-9a-f]\+ //") <(nm -C -D --defined-only --with-symbol-versions giflib-5.1.9/image/usr/lib64/libgif.so | sed -e "s/^[0-9a-f]\+ //")
--- /dev/fd/63
+++ /dev/fd/62
@@ -38,9 +38,6 @@
T EGifSetGifVersion@@Base
T EGifSpew@@Base
T FreeLastSavedImage@@Base
-T GAGetArgs@@Base
-T GAPrintErrMsg@@Base
-T GAPrintHowTo@@Base
T GifAddExtensionBlock@@Base
T GifApplyTranslation@@Base
R GifAsciiTable8x8@@Base
@@ -55,11 +52,7 @@
T GifFreeSavedImages@@Base
T GifMakeMapObject@@Base
T GifMakeSavedImage@@Base
-B GifNoisyPrint@@Base
-T GifQprintf@@Base
-T GifQuantizeBuffer@@Base
T GifUnionColorMap@@Base
-T PrintGifError@@Base
T _ClearHashTable@@Base
T _ExistsHashTable@@Base
T _InitHashTable@@Base
6 other deleted symbols are not declared in gif_lib.h, so they probably do not need to be restored.
The move of GifQuantizeBuffer out of the core library was intentional, to reduce library size and attack surface. It was never part of the documented API.
I have followed through by moving that declaration to getarg.h, which is where the other util library functions are documented. I will add a notice to the upcomonmg poin release that applications requiring this function should link lutil or make their own copy of the code.
If you are breaking the ABI ("Sorry folks, application X will not run anymore. Please rebuild and additionally link against another library") you'll need to bump the soname.
Well, seems like 5.2.0 release even went a step further and no longer adds any .so version at all since commit 72169c45680d028c6465cd11abf6ee5aa4af86f4
possible solution: include a copy of the GifQuantizeBuffer function in downstream packages:
https://github.com/coin3d/simage/pull/33
https://github.com/mono/libgdiplus/pull/575