libkmod-elf: resolve CRC if module is built with MODULE_REL_CRCS

Normally exported symbol's crc is stored as absolute (SHN_ABS)
value of special named symbol __crc_<symbol name>.

When the kernel and modules are built with the config option
CONFIG_MODULE_REL_CRCS, all the CRCs are put in a special section
and the __crc_<symbol name> symbols values are offsets in the
section. See patch description of the commit:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=56067812d5b0e737ac2063e94a50f76b810d6ca3

Add kmod support of this configuration.

Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>

diff --git a/libkmod/libkmod-elf.c b/libkmod/libkmod-elf.c
index 90da89a..ef4a8a3 100644 (file)
--- a/libkmod/libkmod-elf.c
+++ b/libkmod/libkmod-elf.c
@@ -747,6 +747,31 @@ static inline uint8_t kmod_symbol_bind_from_elf(uint8_t elf_value)
        }
 }
 
+static uint64_t kmod_elf_resolve_crc(const struct kmod_elf *elf, uint64_t crc, uint16_t shndx)
+{
+       int err;
+       uint64_t off, size;
+       uint32_t nameoff;
+
+       if (shndx == SHN_ABS || shndx == SHN_UNDEF)
+               return crc;
+
+       err = elf_get_section_info(elf, shndx, &off, &size, &nameoff);
+       if (err < 0) {
+               ELFDBG("Cound not find section index %"PRIu16" for crc", shndx);
+               return (uint64_t)-1;
+       }
+
+       if (crc > (size - sizeof(uint32_t))) {
+               ELFDBG("CRC offset %"PRIu64" is too big, section %"PRIu16" size is %"PRIu64"\n",
+                      crc, shndx, size);
+               return (uint64_t)-1;
+       }
+
+       crc = elf_get_uint(elf, off + crc, sizeof(uint32_t));
+       return crc;
+}
+
 /* array will be allocated with strings in a single malloc, just free *array */
 int kmod_elf_get_symbols(const struct kmod_elf *elf, struct kmod_modversion **array)
 {
@@ -830,6 +855,7 @@ int kmod_elf_get_symbols(const struct kmod_elf *elf, struct kmod_modversion **ar
                uint32_t name_off;
                uint64_t crc;
                uint8_t info, bind;
+               uint16_t shndx;
 
 #define READV(field)                                                   \
                elf_get_uint(elf, sym_off + offsetof(typeof(*s), field),\
@@ -839,11 +865,13 @@ int kmod_elf_get_symbols(const struct kmod_elf *elf, struct kmod_modversion **ar
                        name_off = READV(st_name);
                        crc = READV(st_value);
                        info = READV(st_info);
+                       shndx = READV(st_shndx);
                } else {
                        Elf64_Sym *s;
                        name_off = READV(st_name);
                        crc = READV(st_value);
                        info = READV(st_info);
+                       shndx = READV(st_shndx);
                }
 #undef READV
                name = elf_get_mem(elf, str_off + name_off);
@@ -856,7 +884,7 @@ int kmod_elf_get_symbols(const struct kmod_elf *elf, struct kmod_modversion **ar
                else
                        bind = ELF64_ST_BIND(info);
 
-               a[count].crc = crc;
+               a[count].crc = kmod_elf_resolve_crc(elf, crc, shndx);
                a[count].bind = kmod_symbol_bind_from_elf(bind);
                a[count].symbol = itr;
                slen = strlen(name);