arm: Do not insert stubs needing Arm code on Thumb-only cores.

We recently fixed a bug in libgcc
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115360)
where a symbol was missing a %function .type decoration.

This meant the linker would silently pick the wrong type of 'farcall
stub', involving Arm-mode instructions on Thumb-only CPUs.

This patch emits an error instead, and warns in some other cases, to
encourage users to add the missing '.type foo,%function' directive.

In practice: in arm_type_of_stub() we no longer try to infer which
stub to use if the destination is of unknown type and the CPU is
Thumb-only; so we won't lie to elf32_arm_size_stubs() which does not
check branch_type.

If branch_type is ST_BRANCH_TO_ARM but the CPU is Thumb-only, we now
convert it to ST_BRANCH_TO_THUMB only if the destination is of
absolute type.  This is to support the case where the destination of
the branch is defined by the linker script (see thumb-b-lks-sym.s and
thumb-bl-lks-sym.s testcases for instance).

The motivating case is covered by the new farcall-missing-type
testcase, where we now emit an error message.  We do not emit an error
when branch_type is ST_BRANCH_UNKNOWN and the CPU supports Arm-mode: a
lot of legacy code (e.g. newlib's crt0.S) lacks the corresponding
'.type foo, %function' directives and even a (too verbose) warning
could be perceived as a nuisance.

Existing testcases where such a warning would trigger:
arm-static-app.s (app_func, app_func2)
arm-rel32.s (foo)
arm-app.s (app_func)
rel32-reject.s () main)
fix-arm1176.s (func_to_branch_to)
but this list is not exhaustive.

For the sake of clarity, the patch replaces occurrences of
sym.st_target_internal = 0; with
sym.st_target_internal = ST_BRANCH_TO_ARM;

enum arm_st_branch_type is defined in include/elf/arm.h, and relies on
ST_BRANCH_TO_ARM==0, as sym.st_target_internal is also initialized to
0 in other target-independent parts of BFD code.  (For instance,
swapping the ST_BRANCH_TO_ARM and ST_BRANCH_TO_THUMB entries in the
enum definition leads to 'interesting' results...)

Regarding the testsuite:
* new expected warning for thumb-b-lks-sym and thumb-bl-lks-sym
* new testcase farcall-missing-type to check the new error case
* attr-merge-arch-2b.s, branch-futures (and bfs-1.s) updated to avoid
  a diagnostic

Tested on arm-eabi and arm-pe with no regression.

0 files changed, 0 insertions, 0 deletions