[PATCH] ld (bfd) arm32 elf invalid strings offset in .strtab
Alan Modra
amodra@gmail.com
Thu Aug 22 05:02:00 GMT 2019
On Wed, Aug 21, 2019 at 12:35:03PM +0000, Tamar Christina wrote:
> Hi Alan,
>
> Thanks for the reply,
>
> >
> > This is just piling on horrible hacks. elf32_arm_swap_symbol_in should not
> > be calling bfd_elf_sym_name. I would recommend just deleting
> > ARM_{GET,SET}_SYM_CMSE_SPCL and instead replacing uses of
> > ARM_GET_SYM_CMSE_SPCL with a string compare of the name with
> > CMSE_PREFIX. I don't believe there is any need to use st_target_internal & 4
> > to cache the result of a name comparison, and swap_symbol_in is not the
> > best place to do so in terms of speed.
> >
>
> I may be missing something, but why not? Where would be a better place?
> It seems to me that replacing a simple mask check with strcmp everywhere is a worse option,
> but perhaps I am misunderstanding something here.
Yes, see below. You might be getting more strncmp calls than you
realise.
> > BTW, if you and the ARM maintainers do want to continue with horrible
> > hacks, the following in elf32_arm_swap_symbol_in probably will work.
> >
>
> I am not an ARM maintainer so I can't speak for them,
> but out of interest what makes the change you proposed to be a hack, and what other hack is it layering on top?
Doing the strncmp in swap_symbol_in is the hack (*). As evidenced by
this bug, swap_symbol_in wasn't designed for doing that. Name strings
are set up later (for global symbols anyway). If you're concerned
about speed you don't want to repeat the lookup of st_name in .strtab/
.dynstr. Also for globals you don't want to strncmp on every
__acle_se_foo when loading from the object file since more than one
object file might weakly define __acle_se_foo. Do the strncmp *after*
merging all the __acle_se_foo seen. Or in elf32_arm_link_hash_newfunc
if you really want to be fast, but tricky!
But I don't think speed was the reason why st_target_internal was used
to cache a strncmp result. It was probably more a case of copying
existing practice for other special symbols.
*) Calling it "horrible" was an over-reaction.. I guess I was
reacting to the second of Thierry's patches here
https://sourceware.org/ml/binutils/2019-08/msg00191.html
which was on not-so-good advice from Tamar to hack
bfd_elf_get_elf_syms. The first of Thierry's patches looked better to
me, and had an excellent description of the bug. Adding a symtab_hdr
parameter to all ELF swap_symbol_in functions is reasonable and bomb
proof, but does draw the attention of those pesky global maintainers..
I'm going to apply the following.
----
ARM CMSE symbols
This patch removes use of st_target_internal to cache the result of
comparing symbol names against CMSE_PREFIX. The problem with setting
a bit in st_target_internal in swap_symbol_in is that calling
bfd_elf_sym_name from swap_symbol_in requires symtab_hdr, and you
don't know for sure whether swap_symbol_in is operating on dynsyms
(and thus elf_tdata (abfd)->dynsymtab_hdr should be used) or on the
normal symtab (thus elf_tdata (abfd)->symtab_hdr). You can make an
educated guess based on abfd->flags & DYNAMIC but that relies on
knowing a lot about calls to bfd_elf_get_elf_syms, and is fragile in
the face of possible future changes.
include/
* elf/arm.h (ARM_GET_SYM_CMSE_SPCL, ARM_SET_SYM_CMSE_SPCL): Delete.
bfd/
* elf32-arm.c (cmse_scan): Don't use ARM_GET_SYM_CMSE_SPCL,
instead recognize CMSE_PREFIX in symbol name.
(elf32_arm_gc_mark_extra_sections): Likewise.
(elf32_arm_filter_cmse_symbols): Don't test ARM_GET_SYM_CMSE_SPCL.
(elf32_arm_swap_symbol_in): Don't invoke ARM_SET_SYM_CMSE_SPCL.
diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 97d3726516..a725504c02 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,11 @@
+2019-08-22 Alan Modra <amodra@gmail.com>
+
+ * elf32-arm.c (cmse_scan): Don't use ARM_GET_SYM_CMSE_SPCL,
+ instead recognize CMSE_PREFIX in symbol name.
+ (elf32_arm_gc_mark_extra_sections): Likewise.
+ (elf32_arm_filter_cmse_symbols): Don't test ARM_GET_SYM_CMSE_SPCL.
+ (elf32_arm_swap_symbol_in): Don't invoke ARM_SET_SYM_CMSE_SPCL.
+
2019-08-20 Dennis Zhang <dennis.zhang@arm.com>
* cpu-aarch64.c: New entries for Cortex-A34, Cortex-A65,
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index d1548d6db3..b675fc60c1 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -6002,12 +6002,12 @@ cmse_scan (bfd *input_bfd, struct elf32_arm_link_hash_table *htab,
if (i < ext_start)
{
cmse_sym = &local_syms[i];
- /* Not a special symbol. */
- if (!ARM_GET_SYM_CMSE_SPCL (cmse_sym->st_target_internal))
- continue;
sym_name = bfd_elf_string_from_elf_section (input_bfd,
symtab_hdr->sh_link,
cmse_sym->st_name);
+ if (!sym_name || !CONST_STRNEQ (sym_name, CMSE_PREFIX))
+ continue;
+
/* Special symbol with local binding. */
cmse_invalid = TRUE;
}
@@ -6015,9 +6015,7 @@ cmse_scan (bfd *input_bfd, struct elf32_arm_link_hash_table *htab,
{
cmse_hash = elf32_arm_hash_entry (sym_hashes[i - ext_start]);
sym_name = (char *) cmse_hash->root.root.root.string;
-
- /* Not a special symbol. */
- if (!ARM_GET_SYM_CMSE_SPCL (cmse_hash->root.target_internal))
+ if (!CONST_STRNEQ (sym_name, CMSE_PREFIX))
continue;
/* Special symbol has incorrect binding or type. */
@@ -15990,7 +15988,8 @@ elf32_arm_gc_mark_extra_sections (struct bfd_link_info *info,
/* Assume it is a special symbol. If not, cmse_scan will
warn about it and user can do something about it. */
- if (ARM_GET_SYM_CMSE_SPCL (cmse_hash->root.target_internal))
+ if (CONST_STRNEQ (cmse_hash->root.root.root.string,
+ CMSE_PREFIX))
{
cmse_sec = cmse_hash->root.root.u.def.section;
if (!cmse_sec->gc_mark
@@ -18610,9 +18609,6 @@ elf32_arm_filter_cmse_symbols (bfd *abfd ATTRIBUTE_UNUSED,
|| cmse_hash->root.type != STT_FUNC)
continue;
- if (!ARM_GET_SYM_CMSE_SPCL (cmse_hash->root.target_internal))
- continue;
-
syms[dst_count++] = sym;
}
free (cmse_name);
@@ -19935,9 +19931,6 @@ elf32_arm_swap_symbol_in (bfd * abfd,
const void *pshn,
Elf_Internal_Sym *dst)
{
- Elf_Internal_Shdr *symtab_hdr;
- const char *name = NULL;
-
if (!bfd_elf32_swap_symbol_in (abfd, psrc, pshn, dst))
return FALSE;
dst->st_target_internal = 0;
@@ -19966,13 +19959,6 @@ elf32_arm_swap_symbol_in (bfd * abfd,
else
ARM_SET_SYM_BRANCH_TYPE (dst->st_target_internal, ST_BRANCH_UNKNOWN);
- /* Mark CMSE special symbols. */
- symtab_hdr = & elf_symtab_hdr (abfd);
- if (symtab_hdr->sh_size)
- name = bfd_elf_sym_name (abfd, symtab_hdr, dst, NULL);
- if (name && CONST_STRNEQ (name, CMSE_PREFIX))
- ARM_SET_SYM_CMSE_SPCL (dst->st_target_internal);
-
return TRUE;
}
diff --git a/include/ChangeLog b/include/ChangeLog
index 1813cb38d8..e779c17702 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,3 +1,7 @@
+2019-08-22 Alan Modra <amodra@gmail.com>
+
+ * elf/arm.h (ARM_GET_SYM_CMSE_SPCL, ARM_SET_SYM_CMSE_SPCL): Delete.
+
2019-08-09 Mihailo Stojanovic <mihailo.stojanovic@rt-rk.com>
* elf/mips.h (SHT_GNU_XHASH): New define.
diff --git a/include/elf/arm.h b/include/elf/arm.h
index 5cb9970644..75fb5e26ca 100644
--- a/include/elf/arm.h
+++ b/include/elf/arm.h
@@ -399,11 +399,4 @@ enum arm_st_branch_type {
| ((TYPE) & ENUM_ARM_ST_BRANCH_TYPE_BITMASK))
#endif
-/* Get or set whether a symbol is a special symbol of an entry function of CMSE
- secure code. */
-#define ARM_GET_SYM_CMSE_SPCL(SYM_TARGET_INTERNAL) \
- (((SYM_TARGET_INTERNAL) >> 2) & 1)
-#define ARM_SET_SYM_CMSE_SPCL(SYM_TARGET_INTERNAL) \
- (SYM_TARGET_INTERNAL) |= 4
-
#endif /* _ELF_ARM_H */
--
Alan Modra
Australia Development Lab, IBM
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