The lowest bit of the thumb instruction is 1 by default, which is used to distinguish arm instructions and thumb instructions.
Fixed the problem of misalignment of symbol table when performing binary search
In arm, the lowest bit of the instruction is 1, which is a thumb instruction, and 0, which is an arm instruction.
The nm command was used in mkallsym.sh before, and the result it will return will set the lowest bit of the thumb instruction to 0. There will be a one-byte deviation during binary search, so mkallsyms.py will also set the lowest bit to 0 according to the previous format.
```sh
arm-none-eabi-nm -Cn nuttx | grep hello
0801c384 T hello_main
arm-none-eabi-objdump nuttx -t |grep hello
0801c384 g F .text 0000004c hello_main
arm-none-eabi-readelf nuttx -s |grep hello
4558: 0801c385 76 FUNC GLOBAL DEFAULT 1 hello_main
```
However, in the following case, when you need to find the function address according to the symbol name and execute the corresponding function, the lowest address obtained is 0. It will follow the arm instruction, causing an exception.
```c
void sym_test(void)
{
printf("call sym_test\n");
}
int main(int argc, FAR char *argv[])
{
FAR void *addr = sym_test;
printf("sym_test:%p %pS\n",addr, addr);
printf("sym_test - 1: %pS\n", (char *)addr - 1);
printf("sym_test + 1: %pS\n", (char *)addr + 1);
size_t size;
void (*func)(void);
const struct symtab_s *sym = allsyms_findbyname("sym_test", &size);
printf("sym_test:%p %pS\n",sym, sym);
func = sym->sym_value;
func();
return 0;
}
```
Therefore, you need to change mkallsyms.py back to the correct result and correct the binary search.
Signed-off-by: yinshengkai <yinshengkai@xiaomi.com>
When CONFIG_SYMTAB_ORDEREDBYNAME is selected most code will use
the ordered search function. When it is not selected no code will
use the ordered search function. This change merges the two
functions and varies its behaviour based on the config setting,
such that all callers can simply call the one search function
and get the best behaviour.
An additional configuration option allows leading underscores to
be stripped from symbols being relocated in loaded objects. This
allows toolchains which prefix C symbol with underscores to make
loadable ELF objects.
Squashed commit of the following:
libs/libxx: Fix some confusing in naming. If the directory is called libxx, then the library must be libxx.a (unless perhaps LIBCXX is selected).
libs/: Fix paths in moved library directories.
libs: Brute force move of libc, libnx, and libxx to libs. Cannot yet build it in that configuration.
