* Provide consistent interface to standalone applications to access the 'global_data' structure Provide a doc/README.standalone more useful to users/developers. * Make IceCube MGT5100 FEC driver workmaster
wdenk
21 years ago
parent
27b207fd0a
commit
7784674852
@ -1,156 +1,96 @@ |
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Design Notes on Exporting U-Boot Functions to Standalone Applications: |
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====================================================================== |
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|
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1. Add a field to the global_data structure, the pointer to a jump |
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table. |
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|
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2. Jump table itself is allocated and filled in the same way as the |
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syscall table is (allocated with malloc() after the code has been |
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relocated to RAM); a special function, fixed to the table element |
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number 0, will be added which returns the ABI version so |
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applications can check for compatibility issues. |
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|
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3. It is application's responsibility to check the ABI version and |
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act accordingly. |
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|
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4. Pointer to the global_data is passed to the application in the |
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dedicated register that is used in the U-Boot to hold this |
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pointer. This assumes that the application is built with the same |
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register- allocation flags as the U-Boot itself. (Actually, this |
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is a requirement even now, as the 'go' command does not perform |
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any actions to protect this register against being clobbered by |
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the application). |
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This approach won't work on the x86 architecture. See below. |
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|
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5. Application now calls standard library functions like printf() |
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instead of specially prefixed names like mon_printf() as it did |
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before. Present implementation of these functions (using the |
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system calls mechanism) will be replaced with jump stubs. |
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|
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6. To export additional functions, the following steps will have to be |
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taken: |
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|
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- Add the xxx() U-Boot function to the EXPORT_FUNC list |
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- Add initialization of the appropriate slot in the jump table |
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|
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7. To port to a new architecture, the appropriate stub code should be |
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provided. No other machine-dependent code is used. Once the stub |
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template is available, no additional coding is needed when |
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exporting new U-Boot functions. A pre-processor macro will be used |
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to automatically instantiate the stub definition for each exported |
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function. |
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|
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Note the following: |
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|
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- This approach uses a jump table with fixed slot allocation. That |
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said, to retain the ABI compatibility, no table reordering, |
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inserting new functions in the middle of the list or deleting |
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functions from the list is allowed. Any such action will break the |
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ABI compatibility. |
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|
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- The x86 architecture does not use a dedicated register to store the |
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pointer to the global_data structure. There are the following |
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approaches available: |
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|
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* Pass the global_data pointer to the application in a register or |
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as an additional argument. This requires special machine- |
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dependent startup code to be compiled into the application. |
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|
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* Make the x86 consistent with the rest of architectures and use a |
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dedicated register. This renders one register unusable in the |
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rest of the U-Boot code and thus increases the size of the U-Boot |
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binary and decreases it performance. |
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|
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The following changes will be made: |
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|
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- The syscall handling code will be removed. |
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|
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- The include/_exports.h file will be introduced, containing the list |
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of the exported functions in the following form: |
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1. The functions are exported by U-Boot via a jump table. The jump |
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table is allocated and initialized in the jumptable_init() routine |
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(common/exports.c). Other routines may also modify the jump table, |
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however. The jump table can be accessed as the 'jt' field of the |
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'global_data' structure. The slot numbers for the jump table are |
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defined in the <include/exports.h> header. E.g., to substitute the |
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malloc() and free() functions that will be available to standalone |
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applications, one should do the following: |
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|
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DECLARE_GLOBAL_DATA_PTR; |
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gd->jt[XF_malloc] = my_malloc; |
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gd->jt[XF_free] = my_free; |
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|
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Note that the pointers to the functions all have 'void *' type and |
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thus the compiler cannot perform type checks on these assignments. |
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|
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2. The pointer to the jump table is passed to the application in a |
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machine-dependent way. PowerPC, ARM and MIPS architectures use a |
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dedicated register to hold the pointer to the 'global_data' |
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structure: r29 on PowerPC, r8 on ARM and k0 on MIPS. The x86 |
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architecture does not use such a register; instead, the pointer to |
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the 'global_data' structure is passed as 'argv[-1]' pointer. |
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|
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The application can access the 'global_data' structure in the same |
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way as U-Boot does: |
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DECLARE_GLOBAL_DATA_PTR; |
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printf("U-Boot relocation offset: %x\n", gd->reloc_off); |
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3. The application should call the app_startup() function before any |
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call to the exported functions. Also, implementor of the |
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application may want to check the version of the ABI provided by |
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U-Boot. To facilitate this, a get_version() function is exported |
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that returns the ABI version of the running U-Boot. I.e., a |
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typical application startup may look like this: |
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int my_app (int argc, char *argv[]) |
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{ |
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app_startup (argv); |
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if (get_version () != XF_VERSION) |
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return 1; |
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} |
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|
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4. The default load and start addresses of the applications are as |
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follows: |
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Load address Start address |
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x86 0x00040000 0x00040000 |
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PowerPC 0x00040000 0x00040004 |
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ARM 0x0c100000 0x0c100000 |
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MIPS 0x80200000 0x80200000 |
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For example, the "hello world" application may be loaded and |
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executed on a PowerPC board with the following commands: |
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=> tftp 0x40000 hello_world.bin |
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=> go 0x40004 |
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EXPORT_FUNC(getc) |
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EXPORT_FUNC(tstc) |
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... |
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5. To export some additional function foobar(), the following steps |
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should be undertaken: |
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|
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This list will be used to assign the slot numbers in the jump |
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table, to determine the size of the jump table and to generate the |
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code for the stub functions. |
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- Append the following line at the end of the include/_exports.h |
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file: |
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- The include/exports.h file will be introduced, containing the |
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prototypes of the exported functions and the assigned slot numbers. |
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EXPORT_FUNC(foobar) |
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|
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- The examples/stubs.c file will be introduced, containing the code |
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for the jump stubs for each of the exported functions. |
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- Add the prototype for this function to the include/exports.h |
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file: |
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|
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Implementation Notes on Exporting U-Boot Functions: |
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=================================================== |
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void foobar(void); |
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1. The patch was applied against TOT as of 7/24 12:50 MEST; the |
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resulting images were tested on the following boards: |
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- Add the initialization of the jump table slot wherever |
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appropriate (most likely, to the jumptable_init() function): |
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* lwmon (PowerPC) |
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* trab (ARM) |
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* inca (MIPS) |
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gd->jt[XF_foobar] = foobar; |
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The hello_world application was loaded and executed then: |
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- Increase the XF_VERSION value by one in the include/exports.h |
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file |
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[lwmon] |
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=> tftp 0x40000 /tftpboot/LWMON/hello_world.bin-avn |
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=> go 0x40004 |
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6. The code for exporting the U-Boot functions to applications is |
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mostly machine-independent. The only places written in assembly |
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language are stub functions that perform the jump through the jump |
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table. That said, to port this code to a new architecture, the |
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only thing to be provided is the code in the examples/stubs.c |
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file. If this architecture, however, uses some uncommon method of |
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passing the 'global_data' pointer (like x86 does), one should add |
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the respective code to the app_startup() function in that file. |
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[trab] |
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TRAB # tftp 0xc100000 /tftpboot/TRAB/hello_world.bin-avn |
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TRAB # go 0xc100000 |
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[inca] |
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INCA-IP # tftp 0x80200000 /tftpboot/INCA/hello_world.bin-avn |
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INCA-IP # go 0x80200000 |
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2. As neither of supported x86 boards can be built from the TOT |
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sources currently, the patch build was verified by manually |
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running the following command in the U-Boot top directory: |
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> make -C examples TOPDIR=`pwd` ARCH=i386 CROSS_COMPILE= |
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The rest of the code is mostly machine-independent and was not |
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verified. |
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3. To test the x86 assembly code, a small standalone application was |
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written. It was built and run on the RedHat Linux 8.0 (x86). The |
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application performs a jump using a pointer to jump table and a |
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function's index in it. |
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4. For the MIPS architecture, the linker script is also provided for |
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linking applications. The default linker script places the .text |
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and .data sections too far from each other so that the resulting |
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.bin files span about 256Mb in size. |
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5. Several example applications required updating for the new API. |
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These applications relied upon the bd_t pointer being passed as |
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the 1st argument to the main function; this had changed when the |
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system calls were introduced, but apparently, these applications |
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weren't fixed at that moment. This is fixed now. |
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6. GCC issues warnings for the 'sched' application. Since now the |
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mon_printf() function is renamed to printf(), GCC applies its |
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knowledge of the format specifiers to check the arguments, |
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complaining about ints passed as longs and vice versa. This is not |
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fixed yet. |
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7. Only the hello_world example application was modified to make use |
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of the newly supplied get_version() function. The application now |
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prints two ABI versions, the one that the application was compiled |
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for and the other, actual ABI version. |
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8. The following new files were added: |
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common/exports.c |
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examples/mips.lds |
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examples/stubs.c |
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include/_exports.h |
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include/exports.h |
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doc/README.standalone |
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The following files are no longer used and will be removed: |
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examples/syscall.S |
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include/syscall.h |
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Note that these functions may only use call-clobbered registers; |
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those registers that are used to pass the function's arguments, |
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the stack contents and the return address should be left intact. |
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@ -0,0 +1,87 @@ |
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#include <stddef.h> |
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#include <stdio.h> |
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#include <string.h> |
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void *func[8], **pfunc; |
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typedef struct xxx xxx_t; |
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struct xxx { |
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int dummy; |
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void **pfunc; |
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} q; |
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#define XF_strcpy 3 |
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#define XF_printf 4 |
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#define LABEL(x) \ |
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asm volatile ( \
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#if defined(__i386__) |
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#define EXPORT_FUNC(x) \ |
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asm volatile ( \
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" .globl mon_" #x "\n" \
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"mon_" #x ":\n" \
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" movl %0, %%eax\n" \
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" movl pfunc, %%ecx\n" \
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" jmp *(%%ecx,%%eax)\n" \
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: : "i"(XF_ ## x * sizeof(void *)) : "eax", "ecx"); |
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#elif defined(__powerpc__) |
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#define EXPORT_FUNC(x) \ |
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asm volatile ( \
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" .globl mon_" #x "\n" \
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"mon_" #x ":\n" \
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" lwz %%r11, %0(%%r29)\n" \
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" lwz %%r11, %1(%%r11)\n" \
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" mtctr %%r11\n" \
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" bctr\n" \
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: : "i"(offsetof(xxx_t, pfunc)), "i"(XF_ ## x * sizeof(void *)) : "r11", "r29"); |
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#elif defined(__arm__) |
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#define EXPORT_FUNC(x) \ |
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asm volatile ( \
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" .globl mon_" #x "\n" \
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"mon_" #x ":\n" \
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" ldr ip, [r8, %0]\n" \
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" ldr pc, [ip, %1]\n" \
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: : "i"(offsetof(xxx_t, pfunc)), "i"(XF_ ## x * sizeof(void *)) : "ip"); |
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#elif defined(__mips__) |
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#define EXPORT_FUNC(x) \ |
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asm volatile ( \
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" .globl mon_" #x "\n" \
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"mon_" #x ":\n" \
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" lw $25, %0($26)\n" \
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" lw $25, %1($25)\n" \
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" jr $25\n" \
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: : "i"(offsetof(xxx_t, pfunc)), "i"(XF_ ## x * sizeof(void *)) : "t9"); |
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#else |
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#error [No stub code for this arch] |
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#endif |
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void dummy(void) |
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{ |
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EXPORT_FUNC(printf) |
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EXPORT_FUNC(strcpy) |
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} |
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int main(void) |
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{ |
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#if defined(__i386__) |
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xxx_t *pq; |
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#elif defined(__powerpc__) |
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register volatile xxx_t *pq asm("r29"); |
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#elif defined(__arm__) |
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register volatile xxx_t *pq asm("r8"); |
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#elif defined(__mips__) |
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register volatile xxx_t *pq asm("k0"); |
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#endif |
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char buf[32]; |
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func[XF_strcpy] = strcpy; |
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func[XF_printf] = printf; |
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pq = &q; |
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pq->pfunc = pfunc = func; |
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mon_strcpy(buf, "test"); |
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mon_printf("hi %s %d z\n", buf, 444); |
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return 0; |
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} |
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