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[PATCH 4/10, GAS/ARM] Rework selection of feature bits to base build attributes on
- From: Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>
- To: "binutils at sourceware dot org" <binutils at sourceware dot org>, Richard Earnshaw <richard dot earnshaw at arm dot com>
- Date: Wed, 21 Jun 2017 11:07:19 +0100
- Subject: [PATCH 4/10, GAS/ARM] Rework selection of feature bits to base build attributes on
- Authentication-results: sourceware.org; auth=none
- References: <e1ae3136-5d45-4816-1891-5fa779d7bc5f@foss.arm.com>
Hi,
=== Context ===
This patch is part of a patch series to add support for ARMv8-R
architecture. Its purpose is to set the feature bits on which to decide
what the build attributes should be according to the mode
(autodetection, user specified architecture or CPU, or
-march/-mcpu=all).
=== Motivation ===
Currently, the flags variable which is used to determine the build
attribute is constructed from the instruction used (arm_arch_used and
thumb_arch_used) as well as the user specified architecture or CPU
(selected_cpu). This means when several .arch are specified the
resulting feature bits can be such that no architecture provide them
all and can thus result in incorrect Tag_CPU_arch. See for instance
what having both .arch armv8-a and .arch armv8-m.base would result in.
This is not caught by the testsuite because of further bugs in the
Tag_CPU_arch build attribute value selection logic (see next patch in
the series).
=== Patch description ===
As one would expect, this patch solves the problem by setting flags
from feature bits used if in autodetection mode [1] and from
selected_cpu otherwise. The logic to set arm_ext_v1, arm_ext_v4t and
arm_ext_os feature bits is also moved to only run in autodetection mode
since otherwise the architecture or CPU would have a consistent set of
feature bits already.
[1] No architecture or CPU was specified by the user
ChangeLog entry is as follows:
*** gas/ChangeLog ***
2017-01-26 Thomas Preud'homme <thomas.preudhomme@arm.com>
* config/tc-arm.c (aeabi_set_public_attributes): Populate flags from
feature bits used or selected_cpu depending on whether a CPU was
selected by the user.
=== Testing ===
Testsuite shows no regression when run for arm-none-eabi targets.
Is this ok for master branch?
Best regards,
Thomas
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 72fd1cc9854428577f1f98ab7703bf4dbdb9cbd5..530a27b1cc915846bcc208878925b60ccd003f6d 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -26577,19 +26577,33 @@ aeabi_set_public_attributes (void)
arm_feature_set arm_arch_v8m_base = ARM_ARCH_V8M_BASE;
const cpu_arch_ver_table *p;
- /* Choose the architecture based on the capabilities of the requested cpu
- (if any) and/or the instructions actually used. */
- ARM_MERGE_FEATURE_SETS (flags, arm_arch_used, thumb_arch_used);
- ARM_MERGE_FEATURE_SETS (flags, flags, *mfpu_opt);
- ARM_MERGE_FEATURE_SETS (flags, flags, selected_cpu);
+ /* Autodetection mode, choose the architecture based the instructions
+ actually used. */
+ if (no_cpu_selected ())
+ {
+ ARM_MERGE_FEATURE_SETS (flags, arm_arch_used, thumb_arch_used);
- if (ARM_CPU_HAS_FEATURE (arm_arch_used, arm_arch_any))
- ARM_MERGE_FEATURE_SETS (flags, flags, arm_ext_v1);
+ if (ARM_CPU_HAS_FEATURE (arm_arch_used, arm_arch_any))
+ ARM_MERGE_FEATURE_SETS (flags, flags, arm_ext_v1);
- if (ARM_CPU_HAS_FEATURE (thumb_arch_used, arm_arch_any))
- ARM_MERGE_FEATURE_SETS (flags, flags, arm_ext_v4t);
+ if (ARM_CPU_HAS_FEATURE (thumb_arch_used, arm_arch_any))
+ ARM_MERGE_FEATURE_SETS (flags, flags, arm_ext_v4t);
- selected_cpu = flags;
+ /* We need to make sure that the attributes do not identify us as v6S-M
+ when the only v6S-M feature in use is the Operating System
+ Extensions. */
+ if (ARM_CPU_HAS_FEATURE (flags, arm_ext_os))
+ if (!ARM_CPU_HAS_FEATURE (flags, arm_arch_v6m_only))
+ ARM_CLEAR_FEATURE (flags, flags, arm_ext_os);
+
+ /* Code run during relaxation relies on selected_cpu being set. */
+ selected_cpu = flags;
+ }
+ /* Otherwise, choose the architecture based on the capabilities of the
+ requested cpu. */
+ else
+ flags = selected_cpu;
+ ARM_MERGE_FEATURE_SETS (flags, flags, *mfpu_opt);
/* Allow the user to override the reported architecture. */
if (object_arch)
@@ -26598,12 +26612,6 @@ aeabi_set_public_attributes (void)
ARM_MERGE_FEATURE_SETS (flags, flags, *object_arch);
}
- /* We need to make sure that the attributes do not identify us as v6S-M
- when the only v6S-M feature in use is the Operating System Extensions. */
- if (ARM_CPU_HAS_FEATURE (flags, arm_ext_os))
- if (!ARM_CPU_HAS_FEATURE (flags, arm_arch_v6m_only))
- ARM_CLEAR_FEATURE (flags, flags, arm_ext_os);
-
tmp = flags;
arch = 0;
for (p = cpu_arch_ver; p->val; p++)