ArmPkg/Library/SemihostLib/Arm/GccSemihost.S

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  14
  15 #include <AsmMacroIoLib.h>
  16
  17 /*
  18   Semihosting operation request mechanism
  19
  20   SVC  0x123456  in ARM state (for all architectures)
  21   SVC  0xAB in Thumb state (excluding ARMv7-M)
  22   BKPT 0xAB for ARMv7-M (Thumb-2 only)
  23
  24   R0 - operation type
  25   R1 - block containing all other parametes
  26
  27   lr - must be saved as svc instruction will cause an svc exception and write
  28        the svc lr register. That happens to be the one we are using, so we must
  29        save it or we will not be able to return.
  30  */
  31 ASM_FUNC(GccSemihostCall)
  32   stmfd   sp!, {lr}
  33   svc     #0x123456
  34   ldmfd   sp!, {lr}
  35   bx      lr
  36
  37