From d8147d7053fa848f7f1ce6692c6788224d14869d Mon Sep 17 00:00:00 2001 From: Richard Earnshaw Date: Tue, 11 May 2021 16:18:25 +0100 Subject: [PATCH] arm: correctly decode Tag_THUMB_ISA_use=3 for thumb2 features This was detected when a user accidentally tried to build a shared library using armv8-m.main objects. The resulting error was "warning: thumb-1 mode PLT generation not currently supported". Something was clearly wrong because v8-m.main is a thumb-2 variant. It turns out that the code to detect thumb-2 in object files hadn't been updated for the extended definition of Tag_THUMB_ISA_use to support the value 3, meaning 'work it out for yourself from the architecture tag'; something that is now necessary given that the line between thumb-1 and thumb-2 has become blurred over time. Another problem with the function doing this calculation was that the absence of this tag (implying a default value 0) should mean use of thumb code was NOT permitted. However, the code went on to look at the architecture flags and decide that it could ignore this if the architecture flags said that thumb2 features were available, thus completely ignoring the intended meaning. bfd/ * elf32-arm.c (using_thumb2): Correctly handle Tag_THUMB_ISA_use values 0 and 3. --- bfd/elf32-arm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c index 79b94e836fc..cb567fe82ad 100644 --- a/bfd/elf32-arm.c +++ b/bfd/elf32-arm.c @@ -3888,9 +3888,11 @@ using_thumb2 (struct elf32_arm_link_hash_table *globals) int thumb_isa = bfd_elf_get_obj_attr_int (globals->obfd, OBJ_ATTR_PROC, Tag_THUMB_ISA_use); - if (thumb_isa) + /* No use of thumb permitted, or a legacy thumb-1/2 definition. */ + if (thumb_isa < 3) return thumb_isa == 2; + /* Variant of thumb is described by the architecture tag. */ arch = bfd_elf_get_obj_attr_int (globals->obfd, OBJ_ATTR_PROC, Tag_CPU_arch); /* Force return logic to be reviewed for each new architecture. */ -- 2.30.2