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, 20 insertions, 0 deletions

diff --git a/firmware/export/config.h b/firmware/export/config.h
index 5947ca171e..3e269c287d 100644
--- a/firmware/export/config.h
+++ b/firmware/export/config.h
@@ -710,6 +710,26 @@ Lyre prototype 1 */
 #define ROCKBOX_STRICT_ALIGN 1
 #endif
 
+#if defined(CPU_ARM) && defined(__ASSEMBLER__)
+/* ARMv4T doesn't switch the T bit when popping pc directly, we must use BX */
+.macro ldmpc cond="", order="ia", regs:req
+#if ARM_ARCH == 4 && defined(USE_THUMB)
+    ldm\cond\order sp!, { \regs, lr }
+    bx\cond lr
+#else
+    ldm\cond\order sp!, { \regs, pc }
+#endif
+.endm
+.macro ldrpc cond=""
+#if ARM_ARCH == 4 && defined(USE_THUMB)
+    ldr\cond lr, [sp], #4
+    bx\cond  lr
+#else
+    ldr\cond pc, [sp], #4
+#endif
+.endm
+#endif
+
 #ifndef CODEC_SIZE
 #define CODEC_SIZE 0
 #endif