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[PATCH, ARM 1/7] Consolidate Thumb-1/Thumb-2 ISA detection
- From: "Thomas Preud'homme" <thomas dot preudhomme at foss dot arm dot com>
- To: <binutils at sourceware dot org>
- Date: Thu, 17 Dec 2015 10:14:14 +0800
- Subject: [PATCH, ARM 1/7] Consolidate Thumb-1/Thumb-2 ISA detection
- Authentication-results: sourceware.org; auth=none
This patch is part of a patch series to add support for ARMv8-M to binutils. This specific patch fixes the code responsible for the Thumb ISA detection. ARM backend of GAS contains the macro ARM_ARCH_THUMB2 and its associated variable arm_ext_t2 to determine the extensions that makes a Thumb code being recognized as Thumb-2. However, these are misused in a number of cases and the definition of ARM_ARCH_THUMB2 include some extension that don't contain any Thumb-2 instruction. This patch cleans all that which paves the way for correct Thumb ISA detection when ARMv8-M Baseline comes into the picture.
 For a quick overview of ARMv8-M please refer to the initial cover letter.
The reasoning for each existing use of arm_arch_t2 is as follows:
* move_or_literal_pool: check is for testing availability of specific instructions so use the right extension bit for them
* handle_it_state: likewise
* md_assemble: comment is explicit, only architecture with Thumb-2 can use VFP so arm_arch_t2 is correct here
* md_convert_frag: checking , given a Thumb-2 instruction is present, whether v6t2 extension bit should be set -> no need if any Thumb-2 extension bit is already there so arm_arch_t2 is correct here
* md_apply_fix: checking for availability of bl/blx with extended range which is a feature of ARMv6t2
The patch also adds functions wide_insn_ok () to centralize the logic of what instruction can be promoted from 16bit to 32bit encoding and whether Thumb-2 is needed for a given wide encoding. Although these are two separate decisions to make, the logic is the same when ARMv8-M is out of the picture.
ChangeLog entries are as follow:
*** gas/ChangeLog ***
2015-12-14 Thomas Preud'homme <email@example.com>
* config/tc-arm.c (move_or_literal_pool): Check mov.w, mvm and movw
availability against arm_ext_v6t2 instead of checking arm_arch_t2,
fixing comments along the way.
(handle_it_state): Check arm_ext_v6t2 instead of arm_arch_t2 to
generate IT instruction.
(non_v6t2_wide_only_insn): New function.
(md_assemble): Use above new function to check for invalid wide
instruction for CPU Thumb ISA and to determine what Thumb extension
bit is necessary for that instruction.
(md_apply_fix): Use arm_ext_v6t2 instead of arm_arch_t2 to decide if
branch is out of range.
*** include/opcode/ChangeLog ***
2015-12-10 Thomas Preud'homme <firstname.lastname@example.org>
* arm.h (ARM_ARCH_THUMB2): Add comment explaining its meaning and
remove extension bit not including any Thumb-2 instruction.
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 7289a13994b8dce9f3967e0f124c1d1f99894af3..fddb31a9c1a4f654e6006293915a41f1b7d6d7af 100644
@@ -7848,10 +7848,10 @@ move_or_literal_pool (int i, enum lit_type t, bfd_boolean mode_3)
- if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_arch_t2))
+ if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2))
- /* Check if on thumb2 it can be done with a mov.w or mvn.w
- instruction. */
+ /* Check if on thumb2 it can be done with a mov.w, mvn or
+ movw instruction. */
unsigned int newimm;
@@ -7865,19 +7865,22 @@ move_or_literal_pool (int i, enum lit_type t, bfd_boolean mode_3)
isNegated = TRUE;
+ /* The number can be loaded with a mov.w or mvn
+ instruction. */
if (newimm != (unsigned int) FAIL)
- inst.instruction = (0xf04f0000
+ inst.instruction = (0xf04f0000 /* MOV.W. */
| (inst.operands[i].reg << 8));
+ /* Change to MOVN. */
inst.instruction |= (isNegated ? 0x200000 : 0);
inst.instruction |= (newimm & 0x800) << 15;
inst.instruction |= (newimm & 0x700) << 4;
inst.instruction |= (newimm & 0x0ff);
+ /* The number can be loaded with a movw instruction. */
else if ((v & ~0xFFFF) == 0)
- /* The number can be loaded with a mov.w instruction. */
int imm = v & 0xFFFF;
inst.instruction = 0xf2400000; /* MOVW. */
@@ -17536,7 +17539,7 @@ handle_it_state (void)
if ((implicit_it_mode & IMPLICIT_IT_MODE_THUMB)
- && ARM_CPU_HAS_FEATURE (cpu_variant, arm_arch_t2))
+ && ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2))
/* Automatically generate the IT instruction. */
@@ -17768,6 +17771,22 @@ in_it_block (void)
return now_it.state != OUTSIDE_IT_BLOCK;
+/* Given an OPCODE that is valid in at least one architecture that is not a
+ superset of ARMv6t2, returns whether it only has wide encoding(s). */
+non_v6t2_wide_only_insn (const struct asm_opcode *opcode)
+ /* Thumb-1 wide instruction. */
+ if (opcode->tencode == do_t_blx
+ || opcode->tencode == do_t_branch23
+ || ARM_CPU_HAS_FEATURE (*opcode->tvariant, arm_ext_msr)
+ || ARM_CPU_HAS_FEATURE (*opcode->tvariant, arm_ext_barrier))
+ return TRUE;
+ return FALSE;
md_assemble (char *str)
@@ -17827,24 +17846,24 @@ md_assemble (char *str)
- if (!ARM_CPU_HAS_FEATURE (variant, arm_ext_v6t2))
+ /* Two things are addressed here:
+ 1) Implicit require narrow instructions on Thumb-1.
+ This avoids relaxation accidentally introducing Thumb-2
+ 2) Reject wide instructions in non Thumb-2 cores.
+ Only instructions with narrow and wide variants need to be handled
+ but selecting all non wide-only instructions is easier. */
+ if (!ARM_CPU_HAS_FEATURE (variant, arm_ext_v6t2)
+ && !non_v6t2_wide_only_insn (opcode))
- if (opcode->tencode != do_t_blx && opcode->tencode != do_t_branch23
- && !(ARM_CPU_HAS_FEATURE(*opcode->tvariant, arm_ext_msr)
- || ARM_CPU_HAS_FEATURE(*opcode->tvariant, arm_ext_barrier)))
+ if (inst.size_req == 0)
+ inst.size_req = 2;
+ else if (inst.size_req == 4)
- /* Two things are addressed here.
- 1) Implicit require narrow instructions on Thumb-1.
- This avoids relaxation accidentally introducing Thumb-2
- 2) Reject wide instructions in non Thumb-2 cores. */
- if (inst.size_req == 0)
- inst.size_req = 2;
- else if (inst.size_req == 4)
- as_bad (_("selected processor does not support `%s' in Thumb-2 mode"), str);
+ as_bad (_("selected processor does not support `%s' in Thumb-2 "
+ "mode"), str);
@@ -17879,13 +17898,10 @@ md_assemble (char *str)
ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
/* Many Thumb-2 instructions also have Thumb-1 variants, so explicitly
- set those bits when Thumb-2 32-bit instructions are seen. ie.
- anything other than bl/blx and v6-M instructions.
- The impact of relaxable instructions will be considered later after we
- finish all relaxation. */
- if ((inst.size == 4 && (inst.instruction & 0xf800e800) != 0xf000e800)
- && !(ARM_CPU_HAS_FEATURE (*opcode->tvariant, arm_ext_msr)
- || ARM_CPU_HAS_FEATURE (*opcode->tvariant, arm_ext_barrier)))
+ set those bits when Thumb-2 32-bit instructions are seen. The impact
+ of relaxable instructions will be considered later after we finish all
+ relaxation. */
+ if (inst.size == 4 && !non_v6t2_wide_only_insn (opcode))
ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
@@ -22853,7 +22869,7 @@ md_apply_fix (fixS * fixP,
if ((value & ~0x3fffff) && ((value & ~0x3fffff) != ~0x3fffff))
- if (!(ARM_CPU_HAS_FEATURE (cpu_variant, arm_arch_t2)))
+ if (!(ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6t2)))
as_bad_where (fixP->fx_file, fixP->fx_line, BAD_RANGE);
else if ((value & ~0x1ffffff)
&& ((value & ~0x1ffffff) != ~0x1ffffff))
diff --git a/include/opcode/arm.h b/include/opcode/arm.h
index 286016bbf2a1bc9b3ee58eff9ffae5ccdf602e23..abbe6a82206450aa525b36f3679379d538fe6e1e 100644
@@ -261,10 +261,10 @@
#define ARM_ANY ARM_FEATURE (-1, -1, 0) /* Any basic core. */
#define ARM_FEATURE_ALL ARM_FEATURE (-1, -1, -1)/* All CPU and FPU features. */
#define FPU_ANY_HARD ARM_FEATURE_COPROC (FPU_FPA | FPU_VFP_HARD | FPU_MAVERICK)
+/* Extensions containing some Thumb-2 instructions. If any is present, Thumb
+ ISA is Thumb-2. */
#define ARM_ARCH_THUMB2 ARM_FEATURE_CORE_LOW (ARM_EXT_V6T2 | ARM_EXT_V7 \
- | ARM_EXT_V7A | ARM_EXT_V7R \
- | ARM_EXT_V7M | ARM_EXT_DIV \
- | ARM_EXT_V8)
+ | ARM_EXT_DIV | ARM_EXT_V8)
/* v7-a+sec. */
#define ARM_ARCH_V7A_SEC ARM_FEATURE_CORE_LOW (ARM_AEXT_V7A | ARM_EXT_SEC)
/* v7-a+mp+sec. */
* No regression under binutils testsuite
* Toolchain was built successfully with and without the ARMv8-M support patches with the following multilib list: armv6-m,armv7-m,armv7e-m,cortex-m7,armv8-m.base,armv8-m.main. The code generation for crtbegin.o, crtend.o, crti.o, crtn.o, libgcc.a, libgcov.a, libc.a, libg.a, libgloss-linux.a, libm.a, libnosys.a, librdimon.a, librdpmon.a, libstdc++.a and libsupc++.a is unchanged for all targets supported before the patches.
* Thumb-1 (default arch and --with-mode=thumb) and Thumb-2 (--with-arch=armv7-a --with-mode=thumb) GCC bootstrap using binutils with this patch
* No GCC testsuite regression on fast model compared to ARMv6s-M (Baseline) or ARMv7-M (Mainline)
 including this one, the ld one and the GCC one
Is this ok for master branch?