To get v4t style interworking you need to ensure all your objects are built for v4t. The use of blx should only occur if the linker detects an object file in the input list that already contains support for blx (for example, because it was compiled with v5 or later).
I'm compiling all objects with "-mcpu=arm7tdmi -march=armv4t -mthumb-interwork" and a linker configured with "--with-arch=armv7-a --with-cpu=cortex-a9 --with-tune=cortex-a9" will always emit armv5 style interworking. If I use a linker configured with "--with-arch=armv4t --with-cpu=arm7tdmi --with-tune=arm7tdmi" then I get armv4t style interworking.
----------------------------------------------------------------------------------- This email message is for the sole use of the intended recipient(s) and may contain confidential information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. -----------------------------------------------------------------------------------