FS#11335 by me: make ARM assembly functions thumb-friendly

We can't pop into pc on ARMv4t when using thumb: the T bit won't be
modified if we are returning to a thumb function
Code running on ARMv4t should use the new ldrpc / ldmpc macros instead
of ldr pc, [sp], #4 and ldm(cond) sp!, {regs, pc}
No modification on pure ARM builds and ARMv5+

Note: USE_THUMB is currently never defined, no targets can currently be
built with -mthumb, see FS#6734

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26756 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 9 insertions, 1 deletions

diff --git a/firmware/target/arm/thread-arm.c b/firmware/target/arm/thread-arm.c
index c2d91cec25..9ea3d0bef9 100644
--- a/firmware/target/arm/thread-arm.c
+++ b/firmware/target/arm/thread-arm.c
@@ -77,7 +77,15 @@ static inline void load_context(const void* addr)
     asm volatile(
         "ldr     r0, [%0, #40]          \n" /* Load start pointer */
         "cmp     r0, #0                 \n" /* Check for NULL */
-        "ldmneia %0, { r0, pc }         \n" /* If not already running, jump to start */ 
+
+        /* If not already running, jump to start */
+#if ARM_ARCH == 4 && defined(USE_THUMB)
+        "ldmneia %0, { r0, r12 }        \n"
+        "bxne    r12                    \n"
+#else
+        "ldmneia %0, { r0, pc }         \n"
+#endif
+
         "ldmia   %0, { r4-r11, sp, lr } \n" /* Load regs r4 to r14 from context */
         : : "r" (addr) : "r0" /* only! */
     );