package/qt5webengine: fix no executable stack link issue on arm
TL;DR; This turns the configure flag -no-feature-webengine-noexecstack
to -feature-webengine-noexecstack to workaround a link issue on ARM
32-bit if chromium requests for an executable stack.
And now, the long story...
The configure flag -no-feature-webengine-noexecstack was introduced with
commit 675cbaf9aa (package/qt5/qt5webengine: bump to version 5.15.8).
That configure flag controls the feature webengine-noexecstack[1][2];
the -no-feature-webengine-noexecstack causes qmake to **NOT** append the
linker flags -Wl,-z,noexecstack[3] to QMAKE_LFLAGS.
It results in the linkage issue below on ARM 32-bit at the creation of
its Qt module, i.e. after qmake has built the chromium third party via
gn:
ulimit -n 4096 && /home/gportay/src/buildroot/output/host/bin/arm-buildroot-linux-gnueabihf-g++ --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot @/home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/release/QtWebEngineCore_o.rsp -Wl,--start-group @/home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/release/QtWebEngineCore_a.rsp -Wl,--end-group -Wl,--fatal-warnings -Wl,--build-id=sha1 -fPIC -Wl,-z,relro -Wl,-z,now -Wl,-z,defs -Wl,-O2 -Wl,--gc-sections --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot -Wl,-O1 -Wl,--enable-new-dtags -Wl,-whole-archive -lqtwebenginecoreapi -Wl,-no-whole-archive -Wl,--no-undefined -Wl,--version-script,QtWebEngineCore.version -Wl,-O1 -Wl,--enable-new-dtags -shared -Wl,-soname,libQt5WebEngineCore.so.5 -o libQt5WebEngineCore.so.5.15.14 -latomic /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Quick.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Gui.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5QmlModels.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5WebChannel.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Qml.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Network.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Core.so -lpthread -L/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib -latomic -lGLESv2 -lpthread -ldl -lrt -lnss3 -lnssutil3 -lsmime3 -lplds4 -lplc4 -lnspr4 -levent -lresolv -ljpeg -lopus -lm -lz -lvpx -lpng16 -lwebp -lwebpmux -lwebpdemux -lfreetype -lexpat -lfontconfig -lharfbuzz-subset -lharfbuzz -lsnappy -lxml2 -lxslt -ldbus-1 -L/home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/api/release -lGLESv2 -lrt -lpthread -ldl
/home/gportay/src/buildroot/output/host/lib/gcc/arm-buildroot-linux-gnueabihf/13.3.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: warning: /home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/release/obj/third_party/blink/renderer/platform/heap/asm/asm/SaveRegisters_arm.o: missing .note.GNU-stack section implies executable stack
/home/gportay/src/buildroot/output/host/lib/gcc/arm-buildroot-linux-gnueabihf/13.3.0/../../../../arm-buildroot-linux-gnueabihf/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
collect2: error: ld returned 1 exit status
The link succeeds if the missing linker flags are appended manually to
the command-line:
ulimit -n 4096 && /home/gportay/src/buildroot/output/host/bin/arm-buildroot-linux-gnueabihf-g++ --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot @/home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/release/QtWebEngineCore_o.rsp -Wl,--start-group @/home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/release/QtWebEngineCore_a.rsp -Wl,--end-group -Wl,--fatal-warnings -Wl,--build-id=sha1 -fPIC -Wl,-z,relro -Wl,-z,now -Wl,-z,defs -Wl,-O2 -Wl,--gc-sections --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot -Wl,-O1 -Wl,--enable-new-dtags -Wl,-whole-archive -lqtwebenginecoreapi -Wl,-no-whole-archive -Wl,--no-undefined -Wl,--version-script,QtWebEngineCore.version -Wl,-O1 -Wl,--enable-new-dtags -shared -Wl,-soname,libQt5WebEngineCore.so.5 -o libQt5WebEngineCore.so.5.15.14 -latomic /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Quick.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Gui.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5QmlModels.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5WebChannel.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Qml.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Network.so /home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib/libQt5Core.so -lpthread -L/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot/usr/lib -latomic -lGLESv2 -lpthread -ldl -lrt -lnss3 -lnssutil3 -lsmime3 -lplds4 -lplc4 -lnspr4 -levent -lresolv -ljpeg -lopus -lvpx -lm -lpng16 -lwebp -lwebpmux -lwebpdemux -lfreetype -lexpat -lfontconfig -lharfbuzz-subset -lharfbuzz -lsnappy -lxml2 -lxslt -ldbus-1 -L/home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/api/release -lGLESv2 -lrt -lpthread -ldl -Wl,-z,noexecstack && echo completed
completed
Note: The configure flag is not forwarded to chromium in any manner; its
scope is limited to the Qt WebEngine module. That configure flag appears
to be a workaround if the does not assemble, compile and link the Elf
object correctly[4][5].
The linker flag -z noexecstack is responsible for marking the object as
not requiring an executable stack by adding the section .note.GNU-stack
in the Elf object.
The file SaveRegisters_arm.S is assembled from the command-line below;
there is no noexecstack flag set:
/home/gportay/src/buildroot/output/host/bin/arm-buildroot-linux-gnueabihf-gcc -MMD -MF obj/third_party/blink/renderer/platform/heap/asm/asm/SaveRegisters_arm.o.d -DARM=1 -DUSE_UDEV -DUSE_AURA=1 -DUSE_NSS_CERTS=1 -DUSE_OZONE=1 -DOFFICIAL_BUILD -DTOOLKIT_QT -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DNO_UNWIND_TABLES -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DCR_SYSROOT_HASH=c2e54f675b83a61301dcdb22e8e7a2b85c01d58c -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -Igen -I../../3rdparty/chromium -fPIC -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -fno-unwind-tables -fno-asynchronous-unwind-tables -fPIC -pipe -pthread -std=gnu11 -march=armv7-a -mfloat-abi=hard -mtune=generic-armv7-a -mfpu=vfpv3-d16 -marm -g0 --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot -c ../../3rdparty/chromium/third_party/blink/renderer/platform/heap/asm/SaveRegisters_arm.S -o obj/third_party/blink/renderer/platform/heap/asm/asm/SaveRegisters_arm.o
The GNU assembler supports the assembler flag -Wa,--{,no}execstack to
require, or not, an executable stack for the object to assemble.
The BUILD.gn does **NOT** set it for the assembler files of the blink
third-party; but it does it for boringssl[6] (see also the project file
CMakeLists.txt[7]).
See below what readelf says if the file is assembled manually with the
flag --noexecstack:
$ /home/gportay/src/buildroot/output/host/bin/arm-buildroot-linux-gnueabihf-gcc -MMD -MF obj/third_party/blink/renderer/platform/heap/asm/asm/SaveRegisters_arm.o.d -DARM=1 -DUSE_UDEV -DUSE_AURA=1 -DUSE_NSS_CERTS=1 -DUSE_OZONE=1 -DOFFICIAL_BUILD -DTOOLKIT_QT -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DNO_UNWIND_TABLES -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DCR_SYSROOT_HASH=c2e54f675b83a61301dcdb22e8e7a2b85c01d58c -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -Igen -I../../3rdparty/chromium -fPIC -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -fno-unwind-tables -fno-asynchronous-unwind-tables -fPIC -pipe -pthread -std=gnu11 -march=armv7-a -mfloat-abi=hard -mtune=generic-armv7-a -mfpu=vfpv3-d16 -marm -g0 --sysroot=/home/gportay/src/buildroot/output/host/arm-buildroot-linux-gnueabihf/sysroot -c ../../3rdparty/chromium/third_party/blink/renderer/platform/heap/asm/SaveRegisters_arm.S -o obj/third_party/blink/renderer/platform/heap/asm/asm/SaveRegisters_arm.o -Wa,--noexecstack
$ readelf -a /home/gportay/src/buildroot/output/build/qt5webengine-5.15.14/src/core/release/obj/third_party/blink/renderer/platform/heap/asm/asm/SaveRegisters_arm.o
(...)
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
(...)
[ 4] .note.GNU-stack PROGBITS 00000000 000058 000000 00 0 0 1
The section the linker claims for is now part of the Elf object; and
qmake is now able to link its Qt WebEngine module.
Note: Alternatively, the patching the file SaveRegisters_arm.S to set
explicitly the section in the source file works as well (this reduces
the impact to the very single file causing the link issue):
#if defined(__linux__) && defined(__ELF__)
.section .note.GNU-stack,"",%progbits
#endif
Instead of fixing directly the origin of the issue and setting the
missing assembler flag -Wa,--noexecstack to blink; this works around the
link issue by turning on the feature noexecstack to qtwebengine to force
qmake to link its module using the linker flag -Wl,-z,noexecstack.
[1]: https://github.com/qt/qtwebengine/blob/5.15.14/src/buildtools/configure.json#L353-L357
[2]: https://github.com/qt/qtwebengine/blob/5.15.14/src/buildtools/configure.json#L720-L724
[3]: https://github.com/qt/qtwebengine/blob/5.15.14/src/buildtools/config/linking.pri#L61-L62
[4]: https://github.com/qt/qtwebengine/commit/597359a16a798df3955404200f1fc6833a7425ab
[5]: https://codereview.qt-project.org/c/qt/qtwebengine/+/263545
[6]: https://github.com/qt/qtwebengine-chromium/blob/87-based/chromium/third_party/boringssl/src/util/BUILD.toplevel#L64
[7]: https://github.com/qt/qtwebengine-chromium/blob/87-based/chromium/third_party/boringssl/src/crypto/CMakeLists.txt#L33
Signed-off-by: Gaël PORTAY <gael.portay@rtone.fr>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
Gaël PORTAY