https://sourceware.org/bugzilla/show_bug.cgi?id=27564
Bug ID: 27564
Summary: arm: Use correct address when comparing symbol values
Product: elfutils
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: backends
Assignee: unassigned at sourceware dot org
Reporter: mark at klomp dot org
CC: elfutils-devel at sourceware dot org
Target Milestone: ---
arm32 has special rules for the symbol value.
https://static.docs.arm.com/ihi0044/g/aaelf32.pdf
Section 5.5.3 Symbol Values
• If the symbol addresses a Thumb instruction, its value is the address of the
instruction with bit zero set (in a relocatable object, the section offset with
bit zero set).
This allows a linker to distinguish Arm and Thumb code symbols without having
to refer to the map. An Arm symbol will always have an even value, while a
Thumb symbol will always have an odd value.
We already have ebl_func_addr_mask which is used frame_unwind. But it isn't
consistently used when searching for and matching symbols by address.
This causes e.g. the libabigail ./tests/data/test-read-dwarf/test-libandroid.so
to produce wrong function names:
$ eu-readelf --debug-dump=info ./tests/data/test-read-dwarf/test-libandroid.so
| grep -2 AAssetDir_close | head -4
[ 2498b] subprogram abbrev: 140
low_pc (addr) +0x0000ce62 <AAssetDir_rewind+0x5>
high_pc (data4) 38 (+0x0000ce88
<AAssetDir_close+0x25>)
frame_base (exprloc)
$ eu-readelf -s ./tests/data/test-read-dwarf/test-libandroid.so | grep
AAssetDir_close
500: 0000ce63 38 FUNC GLOBAL DEFAULT 15
AAssetDir_close@@LIBANDROID
1618: 0000ce63 38 FUNC GLOBAL DEFAULT 15 AAssetDir_close
Possible fix:
diff --git a/libdwfl/dwfl_module_addrsym.c b/libdwfl/dwfl_module_addrsym.c
index 2336b602..33841f5d 100644
--- a/libdwfl/dwfl_module_addrsym.c
+++ b/libdwfl/dwfl_module_addrsym.c
@@ -251,7 +251,7 @@ __libdwfl_addrsym (Dwfl_Module *_mod, GElf_Addr _addr,
GElf_Off *off,
struct search_state state =
{
- .addr = _addr,
+ .addr = _addr & ebl_func_addr_mask (_mod->ebl),
.mod = _mod,
.closest_sym = _closest_sym,
.adjust_st_value = _adjust_st_value,
diff --git a/libdwfl/dwfl_module_getsym.c b/libdwfl/dwfl_module_getsym.c
index 8de9a3eb..c46b1310 100644
--- a/libdwfl/dwfl_module_getsym.c
+++ b/libdwfl/dwfl_module_getsym.c
@@ -179,6 +179,7 @@ __libdwfl_getsym (Dwfl_Module *mod, int ndx, GElf_Sym *sym,
GElf_Addr *addr,
break;
}
+ st_value &= ebl_func_addr_mask (mod->ebl);
if (adjust_st_value)
sym->st_value = st_value;
Then eu-readelf produces:
[ 2498b] subprogram abbrev: 140
low_pc (addr) +0x0000ce62 <AAssetDir_close>
high_pc (data4) 38 (+0x0000ce88 <AAsset_read>)
frame_base (exprloc)
We possibly only should do this for STT_FUNC symbols.
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