Fix semihosting on gcc. We need to save lr as svc instruction will change it.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11171 6f19259b-4bc3-4df7-8a09-765794883524

1 files changed, 7 insertions, 1 deletions

diff --git a/ArmPkg/Library/SemihostLib/Arm/GccSemihost.S b/ArmPkg/Library/SemihostLib/Arm/GccSemihost.S
index aa8b16a..2d33664 100755
--- a/ArmPkg/Library/SemihostLib/Arm/GccSemihost.S
+++ b/ArmPkg/Library/SemihostLib/Arm/GccSemihost.S
@@ -26,10 +26,16 @@ INTERWORK_FUNC(GccSemihostCall)
   BKPT 0xAB for ARMv7-M (Thumb-2 only)
   
   R0 - operation type 
-  R1 - block containing all other parametes 
+  R1 - block containing all other parametes
+  
+  lr - must be saved as svc instruction will cause an svc exception and write 
+       the svc lr register. That happens to be the one we are using, so we must
+       save it or we will not be able to return. 
  */
 ASM_PFX(GccSemihostCall):
+  stmfd   sp!, {lr} 

   svc     #0x123456  
+  ldmfd   sp!, {lr}

   bx      lr