215 lines
6.3 KiB
Plaintext
215 lines
6.3 KiB
Plaintext
Copyright (c) 2006 CodeSourcery Inc
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Copyright (c) 2019 Mentor Graphics
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The authors hereby grant permission to use, copy, modify, distribute,
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and license this software and its documentation for any purpose, provided
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that existing copyright notices are retained in all copies and that this
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notice is included verbatim in any distributions. No written agreement,
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license, or royalty fee is required for any of the authorized uses.
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Modifications to this software may be copyrighted by their authors
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and need not follow the licensing terms described here, provided that
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the new terms are clearly indicated on the first page of each file where
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they apply.
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m68k Semihosting Protocol
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-------------------------
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The instruction used to trigger a semihosting request depends on the
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m68k processor variant. On ColdFire, "halt" is used; on other processors
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(which don't implement "halt"), "bkpt #0" may be used.
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Additionally, a special code sequence is used to distinguish
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semihosting requests from other uses of the instruction used to
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trigger it. The semihosting instruction is immediately preceded by a
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"nop" aligned to a 4-byte boundary, and followed by an invalid sentinel
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instruction 0x4e7bf000 ("movec %sp,0"). The debug agent handling the
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semihosting request must adjust the program counter to skip over the
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sentinel instruction before continuing execution.
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Registers d0 and d1 are used to pass parameters to the semihosting call.
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d0 contains a request code. d1 is typically a pointer to a 4-longword
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parameter block, except for the exit and simulator initialization operations
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where it is an immediate integer value.
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The result of the operation is returned in the first word of the
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parameter block. The second word is used to return an errno value,
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encoded per the "Errno Values" section of the RSP documentation in the
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GDB User Manual.
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The supported d0 request codes are:
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#define HOSTED_EXIT 0
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Terminate program execution; send a 'W' stop reply to GDB.
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d1 contains the exit code, as an immediate integer rather than indirectly
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in a parameter block. This semihosting request isn't expected to return.
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#define HOSTED_INIT_SIM 1
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Do simulator initialization, such as allocation of memory for the
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stack and heap. This semihosting request may be triggered from
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startup code (crt0.S).
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On entry to the semihosting request, d1 contains the default initial
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stack pointer as an immediate value, typically the high end of
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memory defined by the linker script. If the simulator needs to
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dynamically allocate memory for the stack, it should set both d1 and
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sp (a7) to the new stack pointer value.
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#define HOSTED_OPEN 2
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Open file; 'Fopen' GDB fileio request.
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d1 points to a parameter block containing:
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[0] pointer to filename
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[1] filename length
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[2] open flags, encoded per the GDB RSP documentation
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[3] mode, encoded per the GDB RSP documentation
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Return values in parameter block:
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[0] file descriptor or -1 on error
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_CLOSE 3
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Close file; 'Fclose' GDB fileio request.
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d1 points to a parameter block containing:
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[0] file descriptor
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_READ 4
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Read from file; 'Fread' GDB fileio request.
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d1 points to a parameter block containing:
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[0] file descriptor
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[1] pointer to buffer
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[2] buffer size
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Return values in parameter block:
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[0] number of bytes read
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_WRITE 5
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Write to file; 'Fwrite' GDB fileio request.
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d1 points to a parameter block containing:
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[0] file descriptor
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[1] pointer to buffer
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[2] byte count
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Return values in parameter block:
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[0] number of bytes written
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_LSEEK 6
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File seek; 'Flseek' GDB fileio request.
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d1 points to a parameter block containing:
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[0] file descriptor
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[1] high word of 64-bit offset
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[2] low word of 64-bit offset
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[3] seek flag, encoded per the GDB RSP documentation
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Return values in parameter block:
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[0] high word of 64-bit result
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[1] low word of 64-bit result
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[2] errno, encoded per the GDB RSP documentation
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#define HOSTED_RENAME 7
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File rename; 'Frename' GDB fileio request.
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d1 points to a parameter block containing:
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[0] oldname pointer
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[1] oldname length
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[2] newname pointer
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[3] newname length
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_UNLINK 8
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File unlink/delete; 'Funlink' GDB fileio request.
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d1 points to a parameter block containing:
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[0] filename pointer
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[1] filename length
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_STAT 9
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File information; 'Fstat' GDB fileio request.
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d1 points to a parameter block containing:
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[0] filename pointer
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[1] filename length
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[2] pointer to stat buf, using the structure definition in the GDB RSP
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documentation
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_FSTAT 10
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File information; 'Ffstat' GDB fileio request.
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d1 points to a parameter block containing:
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[0] file descriptor
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[1] pointer to stat buf, using the structure definition in the GDB RSP
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documentation
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_GETTIMEOFDAY 11
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Get current time; 'Fgettimeofday' GDB fileio request.
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d1 points to a parameter block containing:
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[0] timeval pointer, using the structure definition in the GDB RSP
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documentation
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_ISATTY 12
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Return true if the file descriptor is the GDB console; 'Fisatty' GDB fileio
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request.
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d1 points to a parameter block containing:
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[0] file descriptor
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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#define HOSTED_SYSTEM 13
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System call; 'Fsystem' GDB fileio request.
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d1 points to a parameter block containing:
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[0] command pointer
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[1] command length
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Return values in parameter block:
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[0] return status
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[1] errno, encoded per the GDB RSP documentation
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