On Mon, Nov 18, 2013 at 08:29:05AM -0800, Ian Lance Taylor wrote:
> On Mon, Nov 18, 2013 at 5:11 AM, Jakub Jelinek <ja...@redhat.com> wrote:
> >
> > info->dlpi_addr == 0 is true for executables (but those have also
> > info->dlpi_name set to ""), but not just for those, it is true also
> > for successfully prelinked shared libraries or any other libraries that
> > have been linked at non-zero offset and the dynamic linker managed to mmap
> > them where they were prelinked resp. linked to.
> >
> > BTW, I'm surprised you aren't adding base_address (well, in fact it is
> > actually not base address, but load bias, difference between load address
> > and link base address) to elf_initialize_syminfo created symbol addresses,
> > because all of them should be biased by the load address.
> > And, elf_initialize_syminfo should ignore st_shndx == SHN_UNDEF symbols,
> > those shouldn't be biased but not even entered into the table.
>
> You're right, these are bugs.
So what about this fix then?
Tested on a short testcase that links against a shared library without
debug info and looks up the symbol using backtrace_syminfo.
make check in libbacktrace also passes.
2013-11-18 Jakub Jelinek <ja...@redhat.com>
* elf.c (SHN_UNDEF): Define.
(elf_initialize_syminfo): Add base_address argument. Ignore symbols
with st_shndx == SHN_UNDEF. Add base_address to address fields.
(elf_add): Adjust caller.
--- libbacktrace/elf.c.jj 2013-11-18 12:48:07.000000000 +0100
+++ libbacktrace/elf.c 2013-11-18 17:41:38.903835173 +0100
@@ -98,6 +98,7 @@ dl_iterate_phdr (int (*callback) (struct
#undef EV_CURRENT
#undef SHN_LORESERVE
#undef SHN_XINDEX
+#undef SHN_UNDEF
#undef SHT_SYMTAB
#undef SHT_STRTAB
#undef SHT_DYNSYM
@@ -183,6 +184,7 @@ typedef struct {
b_elf_wxword sh_entsize; /* Entry size if section holds table */
} b_elf_shdr; /* Elf_Shdr. */
+#define SHN_UNDEF 0x0000 /* Undefined section */
#define SHN_LORESERVE 0xFF00 /* Begin range of reserved indices */
#define SHN_XINDEX 0xFFFF /* Section index is held elsewhere */
@@ -342,6 +344,7 @@ elf_symbol_search (const void *vkey, con
static int
elf_initialize_syminfo (struct backtrace_state *state,
+ uintptr_t base_address,
const unsigned char *symtab_data, size_t symtab_size,
const unsigned char *strtab, size_t strtab_size,
backtrace_error_callback error_callback,
@@ -365,7 +368,8 @@ elf_initialize_syminfo (struct backtrace
int info;
info = sym->st_info & 0xf;
- if (info == STT_FUNC || info == STT_OBJECT)
+ if ((info == STT_FUNC || info == STT_OBJECT)
+ && sym->st_shndx != SHN_UNDEF)
++elf_symbol_count;
}
@@ -385,6 +389,8 @@ elf_initialize_syminfo (struct backtrace
info = sym->st_info & 0xf;
if (info != STT_FUNC && info != STT_OBJECT)
continue;
+ if (sym->st_shndx == SHN_UNDEF)
+ continue;
if (sym->st_name >= strtab_size)
{
error_callback (data, "symbol string index out of range", 0);
@@ -393,7 +399,7 @@ elf_initialize_syminfo (struct backtrace
return 0;
}
elf_symbols[j].name = (const char *) strtab + sym->st_name;
- elf_symbols[j].address = sym->st_value;
+ elf_symbols[j].address = sym->st_value + base_address;
elf_symbols[j].size = sym->st_size;
++j;
}
@@ -733,7 +739,7 @@ elf_add (struct backtrace_state *state,
if (sdata == NULL)
goto fail;
- if (!elf_initialize_syminfo (state,
+ if (!elf_initialize_syminfo (state, base_address,
symtab_view.data, symtab_shdr->sh_size,
strtab_view.data, strtab_shdr->sh_size,
error_callback, data, sdata))
Jakub
