Hi,
I wanted to know if it was possible to force ARM backend to compile a function in ARM while the rest is in Thumb mode.
I tried the attributes which is used in GCC but it doesn’t work.
Here is what I tried:
https://pastebin.com/jCr5LPUY
Thanks in advance,
Uvekilledkenny
It's not possible I'm afraid. ARM/Thumb is per-file in Clang.
Tim.
Hi Dimitri,
As I know the following ACLE attributes are not supported in Clang/LLVM at the moment:
attribute((target(“arm”))) attribute
attribute((target(“thumb”))) attribute
But there is a workaround:
attribute((target(“no-thumb-mode”)))
attribute((target(“thumb-mode”)))
The attributes are propagated to a function declaration in IR by the frontend and the backend generated the code according to them:
$ cat test.c
attribute((target(“no-thumb-mode”))) int foo(void)
{
return 0;
}
int main(void)
{
return foo();
}
$ clang -nostdlib -target armv4t-none-eabi -mthumb -c test.c -emit-llvm -S -o -
; ModuleID = ‘test.c’
source_filename = “test.c”
target datalayout = “e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64”
target triple = “thumbv4t-none–eabi”
; Function Attrs: noinline nounwind
define i32 @foo() #0 {
ret i32 0
}
; Function Attrs: noinline nounwind
define i32 @main() #1 {
%1 = alloca i32, align 4
store i32 0, i32* %1, align 4
%2 = call i32 @foo()
ret i32 %2
}
attributes #0 = { noinline nounwind “correctly-rounded-divide-sqrt-fp-math”=“false” “disable-tail-calls”=“false” “less-precise-fpmad”=“false” “no-frame-pointer-elim”=“true” “no-frame-pointer-elim-non-leaf” “no-infs-fp-math”=“false” “no-jump-tables”=“false” “no-nans-fp-math”=“false” “no-signed-zeros-fp-math”=“false” “no-trapping-math”=“false” “stack-protector-buffer-size”=“8” “target-cpu”=“arm7tdmi” “target-features”=“+soft-float-abi,+strict-align,-thumb-mode” “unsafe-fp-math”=“false” “use-soft-float”=“false” }
attributes #1 = { noinline nounwind “correctly-rounded-divide-sqrt-fp-math”=“false” “disable-tail-calls”=“false” “less-precise-fpmad”=“false” “no-frame-pointer-elim”=“true” “no-frame-pointer-elim-non-leaf” “no-infs-fp-math”=“false” “no-jump-tables”=“false” “no-nans-fp-math”=“false” “no-signed-zeros-fp-math”=“false” “no-trapping-math”=“false” “stack-protector-buffer-size”=“8” “target-cpu”=“arm7tdmi” “target-features”=“+strict-align” “unsafe-fp-math”=“false” “use-soft-float”=“false” }
!llvm.module.flags = !{!0, !1}
!llvm.ident = !{!2}
!0 = !{i32 1, !“wchar_size”, i32 4}
!1 = !{i32 1, !“min_enum_size”, i32 4}
!2 = !{!“clang version 4.0.1 (branches/release_40 299654)”}
$ clang -nostdlib -target armv4t-none-eabi -mthumb -c test.c -S -o -
.text
.syntax unified
.eabi_attribute 67, “2.09” @ Tag_conformance
.cpu arm7tdmi
.eabi_attribute 6, 2 @ Tag_CPU_arch
.eabi_attribute 8, 1 @ Tag_ARM_ISA_use
.eabi_attribute 9, 1 @ Tag_THUMB_ISA_use
.eabi_attribute 17, 1 @ Tag_ABI_PCS_GOT_use
.eabi_attribute 20, 1 @ Tag_ABI_FP_denormal
.eabi_attribute 21, 1 @ Tag_ABI_FP_exceptions
.eabi_attribute 23, 3 @ Tag_ABI_FP_number_model
.eabi_attribute 34, 0 @ Tag_CPU_unaligned_access
.eabi_attribute 24, 1 @ Tag_ABI_align_needed
.eabi_attribute 25, 1 @ Tag_ABI_align_preserved
.eabi_attribute 38, 1 @ Tag_ABI_FP_16bit_format
.eabi_attribute 18, 4 @ Tag_ABI_PCS_wchar_t
.eabi_attribute 26, 2 @ Tag_ABI_enum_size
.eabi_attribute 14, 0 @ Tag_ABI_PCS_R9_use
.file “test.c”
‘+soft-float-abi’ is not a recognized feature for this target (ignoring feature)
‘+soft-float-abi’ is not a recognized feature for this target (ignoring feature)
.globl foo
.p2align 2
.type foo,%function
.code 32 @ @foo
foo:
.fnstart
@ BB#0:
mov r0, #0
bx lr
.Lfunc_end0:
.size foo, .Lfunc_end0-foo
.cantunwind
.fnend
.globl main
.p2align 1
.type main,%function
.code 16 @ @main
.thumb_func
main:
.fnstart
@ BB#0:
.save {r7, lr}
push {r7, lr}
.setfp r7, sp
add r7, sp, #0
.pad #8
sub sp, #8
movs r0, #0
str r0, [sp, #4]
bl foo
add sp, #8
pop {r7}
pop {r1}
mov lr, r1
bx lr
.Lfunc_end1:
.size main, .Lfunc_end1-main
.cantunwind
.fnend
.ident “clang version 4.0.1 (branches/release_40 299654)”
.section “.note.GNU-stack”,“”,%progbits
.eabi_attribute 30, 5 @ Tag_ABI_optimization_goals
Thanks,
Evgeny Astigeevich
Senior Compiler Engineer
Compilation Tools
ARM
Hi Dimitri,
As I know the following ACLE attributes are not supported in Clang/LLVM at
the moment:__attribute__((target("arm"))) attribute
__attribute__((target("thumb"))) attribute
But there is a workaround:
__attribute__((target("no-thumb-mode")))
__attribute__((target("thumb-mode")))
Just curious. Why not provide target("arm") and target("thumb")?
The attributes are propagated to a function declaration in IR by the
frontend and the backend generated the code according to them:$ cat test.c
__attribute__((target("no-thumb-mode"))) int foo(void)
{
return 0;
}
int main(void)
{
return foo();
}
$ clang -nostdlib -target armv4t-none-eabi -mthumb -c test.c -emit-llvm -S
-o -; ModuleID = 'test.c'
source_filename = "test.c"
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "thumbv4t-none--eabi"
; Function Attrs: noinline nounwind
define i32 @foo() #0 {
ret i32 0
}
; Function Attrs: noinline nounwind
define i32 @main() #1 {
%1 = alloca i32, align 4
store i32 0, i32* %1, align 4
%2 = call i32 @foo()
ret i32 %2
}
attributes #0 = { noinline nounwind "correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false" "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-jump-tables"="false"
"no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
"no-trapping-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="arm7tdmi" "target-features"="+soft-float-abi,+strict-align,
*-thumb-mode*" "unsafe-fp-math"="false" "use-soft-float"="false" }attributes #1 = { noinline nounwind "correctly-rounded-divide-sqrt-fp-math"="false"
"disable-tail-calls"="false" "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-jump-tables"="false"
"no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
"no-trapping-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="arm7tdmi" "target-features"="+strict-align"
"unsafe-fp-math"="false" "use-soft-float"="false" }
I don't know if I am reading this wrong (not try this by myself). I see
you apply target("no-thumb-mode") attribute on function foo, yet foo's
attribute #0 has -thumb-mode? Seems to be contradiction?
Regards,
chenwj
Hi,
attribute((target(“no-thumb-mode”)))
attribute((target(“thumb-mode”)))
Just curious. Why not provide target(“arm”) and target(“thumb”)?
I think there is no code converting them into corresponding target(“no-thumb-mode”) and target(“thumb-mode”) in the frontend.
I don’t know if I am reading this wrong (not try this by myself). I see you apply target(“no-thumb-mode”) attribute on function foo, yet foo’s attribute #0 has -thumb-mode? Seems to be contradiction?
In target-features “+attribute” means it is turned on, “-attribute” means it is turned off.
Thanks,
Evgeny
Wow, I am out of the loop! Thanks Evgeny.
Tim.