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authorMartin Dorwig <dorwig@tetronik.com>2015-01-26 15:22:54 -0700
committerSimon Glass <sjg@chromium.org>2015-01-29 17:09:57 -0700
commit49cad54788a64a296567abadcd736fdbe47cc3a3 (patch)
tree8bf86512da0c8f5537743ba745b8f0084119bd2f /doc/README.standalone
parent2017aaef8c383c910e791bf0f87fa4d6b78f5945 (diff)
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Export redesign
this is an atempt to make the export of functions typesafe. I replaced the jumptable void ** by a struct (jt_funcs) with function pointers. The EXPORT_FUNC macro now has 3 fixed parameters and one variadic parameter The first is the name of the exported function, the rest of the parameters are used to format a functionpointer in the jumptable, the EXPORT_FUNC macros are expanded three times, 1. to declare the members of the struct 2. to initialize the structmember pointers 3. to call the functions in stubs.c Signed-off-by: Martin Dorwig <dorwig@tetronik.com> Acked-by: Simon Glass <sjg@chromium.org> Signed-off-by: Simon Glass <sjg@chromium.org> (resending to the list since my tweaks are not quite trivial)
Diffstat (limited to 'doc/README.standalone')
-rw-r--r--doc/README.standalone41
1 files changed, 30 insertions, 11 deletions
diff --git a/doc/README.standalone b/doc/README.standalone
index e3000ef..659a12f 100644
--- a/doc/README.standalone
+++ b/doc/README.standalone
@@ -5,18 +5,18 @@ Design Notes on Exporting U-Boot Functions to Standalone Applications:
table is allocated and initialized in the jumptable_init() routine
(common/exports.c). Other routines may also modify the jump table,
however. The jump table can be accessed as the 'jt' field of the
- 'global_data' structure. The slot numbers for the jump table are
+ 'global_data' structure. The struct members for the jump table are
defined in the <include/exports.h> header. E.g., to substitute the
malloc() and free() functions that will be available to standalone
applications, one should do the following:
DECLARE_GLOBAL_DATA_PTR;
- gd->jt[XF_malloc] = my_malloc;
- gd->jt[XF_free] = my_free;
+ gd->jt->malloc = my_malloc;
+ gd->jt->free = my_free;
- Note that the pointers to the functions all have 'void *' type and
- thus the compiler cannot perform type checks on these assignments.
+ Note that the pointers to the functions are real function pointers
+ so the compiler can perform type checks on these assignments.
2. The pointer to the jump table is passed to the application in a
machine-dependent way. PowerPC, ARM, MIPS, Blackfin and Nios II
@@ -65,27 +65,46 @@ Design Notes on Exporting U-Boot Functions to Standalone Applications:
=> tftp 0x40000 hello_world.bin
=> go 0x40004
-5. To export some additional function foobar(), the following steps
+5. To export some additional function long foobar(int i,char c), the following steps
should be undertaken:
- Append the following line at the end of the include/_exports.h
file:
- EXPORT_FUNC(foobar)
+ EXPORT_FUNC(foobar, long, foobar, int, char)
+
+ Parameters to EXPORT_FUNC:
+ - the first parameter is the function that is exported (default implementation)
+ - the second parameter is the return value type
+ - the third parameter is the name of the member in struct jt_funcs
+ this is also the name that the standalone application will used.
+ the rest of the parameters are the function arguments
- Add the prototype for this function to the include/exports.h
file:
- void foobar(void);
+ long foobar(int i, char c);
+
+ Initialization with the default implementation is done in jumptable_init()
+
+ You can override the default implementation using:
- - Add the initialization of the jump table slot wherever
- appropriate (most likely, to the jumptable_init() function):
+ gd->jt->foobar = another_foobar;
- gd->jt[XF_foobar] = foobar;
+ The signature of another_foobar must then match the declaration of foobar.
- Increase the XF_VERSION value by one in the include/exports.h
file
+ - If you want to export a function which depends on a CONFIG_XXX
+ use 2 lines like this:
+ #ifdef CONFIG_FOOBAR
+ EXPORT_FUNC(foobar, long, foobar, int, char)
+ #else
+ EXPORT_FUNC(dummy, void, foobar, void)
+ #endif
+
+
6. The code for exporting the U-Boot functions to applications is
mostly machine-independent. The only places written in assembly
language are stub functions that perform the jump through the jump