arm64 linux library need GLIBC_2.29

[zx950921]

glibc 2.29 version too high, I tried compiling with Ubuntu 18.04, but It still need to rely on glibc 2.29 in the end, How to downgrade glibc version to at least 2.27?

https://github.com/zx950921/pdfium-binaries/runs/6945770416?check_suite_focus=true#step:13:69

[bblanchon]

I just spent three hours trying to find a solution to this problem; here are my conclusions.

First, I observed that this problem only occurs on ARM64, not ARM.

As far as I can tell, this dependency on glibc 2.29 comes from the sysroot used to build chromium: https://source.chromium.org/chromium/chromium/src/+/main:build/linux/sysroot_scripts/install-sysroot.py

I could track down the symbols here in pdfium/build/linux/debian_bullseye_amd64-sysroot/debian/libc6/DEBIAN/symbols, line 3305:

 pow10@GLIBC_2.2.5 2.2.5
 pow10f@GLIBC_2.2.5 2.2.5
 pow10l@GLIBC_2.2.5 2.2.5
 pow@GLIBC_2.2.5 2.2.5
 pow@GLIBC_2.29 2.29
 powf128@GLIBC_2.26 2.26
 powf32@GLIBC_2.27 2.27
 powf32x@GLIBC_2.27 2.27
 powf64@GLIBC_2.27 2.27
 powf64x@GLIBC_2.27 2.27
 powf@GLIBC_2.2.5 2.2.5
 powf@GLIBC_2.27 2.27
 powl@GLIBC_2.2.5 2.2.5

Strangely, pow, exp, and log are among the few duplicated symbols in this list. I wonder if it's a bug in the sysroot...

From what I understood, the following script patches the sysroot to lower the required glibc version to 2.17: https://source.chromium.org/chromium/chromium/src/+/main:build/linux/sysroot_scripts/reversion_glibc.py;drc=f6901be733e76832721ad7fb8d4d51715df77095

This script is run by the following script: https://source.chromium.org/chromium/chromium/src/+/main:build/linux/sysroot_scripts/sysroot-creator.sh;drc=8161edc5a2ee57e0aa7dee00a9ef3579f87326e4

Interestingly, on line 426, we can see that the invocation is skipped with the comment:

 # Skip reversion_glibc.py. Glibc is compiled in a way where many libm math
 # functions do not have compatibility symbols for versions <= 2.17.

This fairly recent (April 4th) change was introduced in the following commit: https://chromium.googlesource.com/chromium/src/build/+/04efde6a08d590775ced1a3cb0509c0690dbaabb

The commit message says:

Symbol reversioning is disabled altogether for ARM64

Disable glibc symbols with no supported version

reversion_glibc.py rewrites the default version of symbols if it is higher than GLIBC_2.17 and another version <= 2.17 exists. On the other hand, if there is no sufficiently old version available, it left it alone.

This CL changes it to disable these symbols either way.

A list of exceptions is added: the linux-chromeos build makes a few syscalls that aren't supported in glibc 2.17. We want to continue supporting this configuration.

I tried checking a version older than this commit but got the same error.

I'll stop working on this until I get more information.

[mara004]

Many thanks for the detailed investigation. Have you considered contacting upstream about these matters through pdfium's mailing list or bug tracker?

[bblanchon]

No, I haven't because I don't know this topic at all so I wouldn't know what to ask.

[zx950921]

Thank you very much for your help, the complexity of this problem seems to be beyond my knowledge level and can only be tried to solve later

[bblanchon]

I posted a question on the PDFium mailing list: https://groups.google.com/g/pdfium/c/--TpUDMv4s8/m/H0gYjZ9vBAAJ

PS: also on Chromium's mailing list: https://groups.google.com/a/chromium.org/g/chromium-dev/c/SdCs9k3celo/m/TMJqiKYaBQAJ

[mara004]

I tried checking a version older than this commit but got the same error.

Hmm, theoretically I'd believe patching sysroot-creator.sh to enable symbol reversioning should do the trick. However, as far as I understand, the tooling just downloads a sysroot image from Google storage, so to make changes to sysroot-creator.sh take effect, I suppose one would have to rebuild the sysroot locally - did you do this when you rolled back to an older commit?

(Disclaimer: This is just an idea, I only took a brief look and my guess might well be wrong.)

[mara004]

Quoting Lei Zhang:

This issue recently got resolved in https://crrev.com/1084974, and PDFium will pick up that change in the very near future.

[mara004]

@bblanchon I think this issue can be closed?