Hello,

Thank you for your feedback and questions about the ARM64EC patch.
I’m sharing the build system patch for enabling ARM64EC support in FFmpeg.
This patch addresses .def file generation for ARM64EC builds on Windows.

In-Lined patch:

diff --git a/compat/windows/makedef b/compat/windows/makedef
index add8222d13..59e300ab61 100755
--- a/compat/windows/makedef
+++ b/compat/windows/makedef
@@ -108,7 +108,12 @@ if [ -n "$NM" ]; then
               cut -d' ' -f3 |
               sed -e "s/^${prefix}//")
 else
-    dump=$(dumpbin.exe -linkermember:1 ${libname} |
+    member=1
+    arch=$VSCMD_ARG_TGT_ARCH
+    if [ "${arch^^}" = "ARM64EC" ]; then
+        member=32
+    fi
+        dump=$(dumpbin.exe -linkermember:${member} ${libname} |
               sed -e '/public symbols/,$!d' -e '/^ \{1,\}Summary/,$d' -e "s/ \{1,\}${prefix}/ /" -e 's/ \{1,\}/ /g' |
               tail -n +2 |
               cut -d' ' -f3)
@@ -121,7 +126,7 @@ list=""
 for exp in ${regex}; do
     list="${list}"'
 '$(echo "${dump}" |
-          grep "^${exp}" |
+          grep "^${exp}" | awk '!/\$exit_thunk/{print}' |
           sed -e 's/^/    /')
 done

--
2.50.0.windows.1

For reference, here is the configuration used to build FFmpeg with MSVC for ARM64EC:
I've also attached the same configuration in ffmpeg-arm64ec-msvc.config for convenience.

# find_ar_lib resolves to /usr/share/automake-1.16/ar-lib
AR_LIB="$(find_ar_lib)"
AR_CMD="${AR_LIB} lib.exe -machine:arm64ec"
ARCH="arm64"

"${SRC_DIR}/configure" \
    --toolchain=msvc \
    --target-os=win64 \
    --cc=cl.exe \
    --cxx=cl.exe \
    --extra-cxxflags="-arm64EC" \
    --extra-cflags="-arm64EC" \
    --extra-ldflags="/machine:arm64ec" \
    --as="armasm64.exe -machine ARM64EC" \
    --ld=link.exe \
    --ar="${AR_CMD}" \
    --arch="${ARCH}"

In my setup, this configuration requires the gas-preprocessor.pl patch, as the build otherwise ends with a “GNU assembler not found” error.

Thanks,
Harish Raja Selvan.