nuttx/libs/libc/symtab
yinshengkai 97096bed83 libs: fix the problem that the address obtained in thumb mode cannot be executed.
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>
2024-01-04 09:22:57 -08:00
..
CMakeLists.txt build: add initial cmake build system 2023-07-08 13:50:48 +08:00
Kconfig libc/symtab: Move SYMTAB_XXX from unistd/Kconfig to symtab/Kconfig 2023-07-10 13:09:47 -03:00
Make.defs
symtab_allsyms.c libc/symtab: Don't include symtab.h in the header files 2023-07-10 23:03:17 +03:00
symtab_findbyname.c
symtab_findbyvalue.c libs: fix the problem that the address obtained in thumb mode cannot be executed. 2024-01-04 09:22:57 -08:00
symtab_sortbyname.c