buildroot/package/qt5/qt5webengine/0003-configure.pri-remove-some-of-the-thumb-detection-log.patch

From b00f7b41ffdee03f9982287d61c2fa21ebee5e6b Mon Sep 17 00:00:00 2001
From: Arnout Vandecappelle <arnout@rnout.be>
Date: Sat, 17 May 2025 22:09:32 +0200
Subject: [PATCH] configure.pri: remove some of the thumb detection logic

The hasThumbFlag test has a roundabout way of discovering whether thumb
is available. It looks at the -mthumb and -marm flag (which does make
some sense), but then it tries to look at -march to determine which ARM
architecture version is used. That test doesn't work if GCC is
configured for a default target architecture and no -march is passed on
the command line.

In Buildroot, we don't pass any -mthumb, -marm or -march in CFLAGS
because all of that is included in the toolchain wrapper. Therefore, the
logic has nothing to determine the target ARM ISA version and returns
false.

As a result, nothing is passed down to gn, and gn adds -marm to the
build. There is in fact a warning about this:

    WARNING: Thumb instruction set is required to build ffmpeg for QtWebEngine.

but since it's just a warning, it gets ignored.

Indeed, the build does fail (when ffmpeg is built, i.e. when
BR2_PACKAGE_QT5WEBENGINE_PROPRIETARY_CODECS is enabled) with:

    FAILED: obj/third_party/ffmpeg/ffmpeg_internal/vp8.o
    [...]
    {standard input}: Assembler messages:
    {standard input}:1119: Error: bad instruction `ldrhcs r0,[ip],#2'
    {standard input}:1156: Error: bad instruction `ldrhcs r9,[ip],#2'

In practice, the architecture version doesn't really matter, because all
the architectures supported by JSCore have thumb.

Therefore, remove the logic for detecting if the CPU architecture
supports thumb. Do keep the -marm and -mthumb logic, even though in
Buildroot it doesn't do anything, and the warning gets ignored.

Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
Upstream: It's not clear if the same logic about JSCore applies in
upstream, so not sent.
---
 configure.pri | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/configure.pri b/configure.pri
index 8da334c83..3ff298e9f 100644
--- a/configure.pri
+++ b/configure.pri
@@ -370,14 +370,6 @@ defineTest(qtConfTest_hasThumbFlag) {
     !isEmpty(FLAG): return(true)
     FLAG = $$qtwebengine_extractCFlag("-marm")
     !isEmpty(FLAG): return(false)
-
-    MARCH = $$qtwebengine_extractCFlag("-march=.*")
-    MARMV = $$replace(MARCH, "armv",)
-    !isEmpty(MARMV) {
-        MARMV = $$split(MARMV,)
-        MARMV = $$member(MARMV, 0)
-    }
-    if (isEmpty(MARMV) | lessThan(MARMV, 7)): return(false)
     # no flag assume mthumb
     return(true)
 }
-- 
2.49.0