On 2021-06-18, H.J. Lu via llvm-dev wrote:
Add GNU_PROPERTY_1_NEEDED:
#define GNU_PROPERTY_1_NEEDED GNU_PROPERTY_UINT32_OR_LO
to indicate the needed properties by the object file.
I am fine with this logical OR style usage. But see below, do we need it
for ld.so runtime check?
(As I mentioned previously, I do not know how an AND-style property can
be used/deployed if old object files without the .note.gnu.property is
considered to have a value of 0.)
Add GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION:
#define GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION (1U << 0)
to indicate that the object file requires canonical function pointers and
cannot be used with copy relocation.
In https://sourceware.org/pipermail/gnu-gabi/2021q2/000481.html you gave
a rationale
"The issue is that libfoo.so used in link-time can be different from
libfoo.so at run-time. The symbol, foobar, in libfoo.so at link-time
has the default visibility. But foobar in libfoo.so at run-time can be
protected. ld.so should detect such cases which can lead to run-time
failures."
First, I think such dynamic symbol visibility change is uncommon.
Second, if ld.so finds that a symbol lookup for (st_value==0
st_shndx==SHN_UNDEF) will bind to a STV_PROTECTED definition in a shared
object, can the diagnostic be moved there?
The compatibility property is per-symbol and the symbol lookup is a
perfect place for a diagnostic, like a symbol versioning error.
I guess GCC folks may get noticed if you start a thread adding
-fsingle-global-definition, otherwise many people who have opinions may
just ignore threads about GNU PROPERTY addition.
The PDF file is at
https://gitlab.com/x86-psABIs/Linux-ABI/-/wikis/uploads/9eca2f2defe62b0c5015bf2e3e8a9f05/Linux-gABI-1_needed-2021-06-18.pdf
