Home | History | Annotate | Line # | Download | only in gdb.base 
      1 /* This test program is part of GDB, the GNU debugger.
      2 
      3    Copyright 2020-2024 Free Software Foundation, Inc.
      4 
      5    This program is free software; you can redistribute it and/or modify
      6    it under the terms of the GNU General Public License as published by
      7    the Free Software Foundation; either version 3 of the License, or
      8    (at your option) any later version.
      9 
     10    This program is distributed in the hope that it will be useful,
     11    but WITHOUT ANY WARRANTY; without even the implied warranty of
     12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     13    GNU General Public License for more details.
     14 
     15    You should have received a copy of the GNU General Public License
     16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
     17 
     18 /* Simulates loading of JIT code by memory mapping a compiled
     19    shared library binary and doing minimal post-processing.  */
     20 
     21 #include <elf.h>
     22 #include <errno.h>
     23 #include <fcntl.h>
     24 #include <link.h>
     25 #include <stdint.h>
     26 #include <stdio.h>
     27 #include <stdlib.h>
     28 #include <string.h>
     29 #include <sys/mman.h>
     30 #include <sys/stat.h>
     31 #include <unistd.h>
     32 
     33 /* ElfW is coming from linux. On other platforms it does not exist.
     34    Let us define it here. */
     35 #ifndef ElfW
     36 #if (defined(_LP64) || defined(__LP64__))
     37 #define WORDSIZE 64
     38 #else
     39 #define WORDSIZE 32
     40 #endif /* _LP64 || __LP64__  */
     41 #define ElfW(type) _ElfW (Elf, WORDSIZE, type)
     42 #define _ElfW(e, w, t) _ElfW_1 (e, w, _##t)
     43 #define _ElfW_1(e, w, t) e##w##t
     44 #endif /* !ElfW  */
     45 
     46 /* Find symbol with the name `sym_name`.  */
     47 static void *
     48 load_symbol (void *addr, const char *sym_name)
     49 {
     50   const ElfW (Ehdr) *const ehdr = (ElfW (Ehdr) *) addr;
     51   ElfW (Shdr) *const shdr = (ElfW (Shdr) *) ((char *) addr + ehdr->e_shoff);
     52 
     53   ElfW (Addr) sym_old_addr = 0;
     54   ElfW (Addr) sym_new_addr = 0;
     55 
     56   /* Find `func_name` in symbol_table and return its address.  */
     57   int i;
     58   for (i = 0; i < ehdr->e_shnum; ++i)
     59     {
     60       if (shdr[i].sh_type == SHT_SYMTAB)
     61 	{
     62 	  ElfW (Sym) *symtab = (ElfW (Sym) *) (addr + shdr[i].sh_offset);
     63 	  ElfW (Sym) *symtab_end
     64 	      = (ElfW (Sym) *) (addr + shdr[i].sh_offset + shdr[i].sh_size);
     65 	  char *const strtab
     66 	      = (char *) (addr + shdr[shdr[i].sh_link].sh_offset);
     67 
     68 	  ElfW (Sym) *p;
     69 	  for (p = symtab; p < symtab_end; ++p)
     70 	    {
     71 	      const char *s = strtab + p->st_name;
     72 	      if (strcmp (s, sym_name) == 0)
     73 	        return (void *) p->st_value;
     74 	    }
     75 	}
     76     }
     77 
     78   fprintf (stderr, "symbol '%s' not found\n", sym_name);
     79   exit (1);
     80   return 0;
     81 }
     82 
     83 /* Open an elf binary file and memory map it with execution flag enabled.  */
     84 static void *
     85 load_elf (const char *libname, size_t *size, void *load_addr)
     86 {
     87   int fd;
     88   struct stat st;
     89 
     90   if ((fd = open (libname, O_RDONLY)) == -1)
     91     {
     92       fprintf (stderr, "open (\"%s\", O_RDONLY): %s\n", libname,
     93 	       strerror (errno));
     94       exit (1);
     95     }
     96 
     97   if (fstat (fd, &st) != 0)
     98     {
     99       fprintf (stderr, "fstat (\"%d\"): %s\n", fd, strerror (errno));
    100       exit (1);
    101     }
    102 
    103   void *addr = mmap (load_addr, st.st_size,
    104   		     PROT_READ | PROT_WRITE | PROT_EXEC,
    105 		     load_addr != NULL ? MAP_PRIVATE | MAP_FIXED : MAP_PRIVATE,
    106 		     fd, 0);
    107   close (fd);
    108 
    109   if (addr == MAP_FAILED)
    110     {
    111       fprintf (stderr, "mmap: %s\n", strerror (errno));
    112       exit (1);
    113     }
    114 
    115   if (size != NULL)
    116     *size = st.st_size;
    117 
    118   return addr;
    119 }
    120