From: Alex Kiernan <[email protected]>
llvm_features_from_tune() calls target_is_armv7() to gate both the +v7
LLVM feature and the +thumb2 feature. target_is_armv7() (in
rust-common.bbclass) only recognises armv7a/armv7r/armv7m/armv7ve -- it
returns False for armv8a. As a result an ARMv8-A AArch32 Thumb build
gets "+neon,+thumb-mode" in the target JSON but neither "+v8" nor
"+thumb2".
LLVM's ParseARMTriple() returns "" for "arm-..." triples
(ARM::parseArch("arm") = INVALID), leaving HasV4TOps unset in the
MCSubtargetInfo used for module-level inline asm parsing. The ARM ASM
parser's hasThumb() then returns false and ".thumb" directives in
compiler_builtins naked-function trampolines (__aeabi_uldivmod etc.)
are rejected.
This produces two failures when building libstd-rs / compiler_builtins:
1. core: "LLVM ERROR: Cannot select: br" in core::fmt::num -- LLVM ARM
ISel patterns for Thumb-2 unconditional branches (t2B) are gated on
HasV8Ops as well as IsThumb2; without +v8 the pattern never fires.
2. compiler_builtins: "target does not support Thumb mode" on .thumb
directives in naked-function trampolines (__aeabi_uldivmod etc.) --
two separate paths both require +thumb2: HasV4TOps in the
MCSubtargetInfo (set transitively via ParseARMTriple) and
FeatureThumb2 in the code-gen ARMSubtarget.
The natural fix would be to change RUST_TARGET_SYS to "armv8a-...", but
"armv8a" is not a recognised Rust target architecture so the triple is
not valid there. Instead rust_sys_to_llvm_target() rewrites only the
JSON llvm-target field, leaving RUST_TARGET_SYS and rust-common.bbclass
unchanged.
- Add +v8 to llvm_features_from_tune for armv8a AArch32.
- Add +thumb2 to llvm_features_from_tune for armv8a AArch32 Thumb.
- Extend rust_sys_to_llvm_target() to accept the datastore and rewrite
the "arm-..." triple to "armv8a-..." for armv8a AArch32 targets, so
the JSON llvm-target field uses "armv8a-..." while RUST_TARGET_SYS
keeps "arm-...". ParseARMTriple then adds "+armv8-a" to the
MCSubtargetInfo, transitively setting HasV4TOps and making hasThumb()
return true.
The TARGET_ARCH == 'arm' guard is required because AArch64 tunes also
carry armv8a in TUNE_FEATURES (via arch-armv8a.inc) but must not be
affected.
AI-Generated: Claude Code (Claude Opus 4.8)
Signed-off-by: Alex Kiernan <[email protected]>
Signed-off-by: Alex Kiernan <[email protected]>
---
meta/classes-recipe/rust-target-config.bbclass | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/meta/classes-recipe/rust-target-config.bbclass
b/meta/classes-recipe/rust-target-config.bbclass
index 941fe1958361..6acbe5e68834 100644
--- a/meta/classes-recipe/rust-target-config.bbclass
+++ b/meta/classes-recipe/rust-target-config.bbclass
@@ -19,6 +19,8 @@ def llvm_features_from_tune(d):
mach_overrides = d.getVar('MACHINEOVERRIDES')
mach_overrides = frozenset(mach_overrides.split(':'))
+ target_arch = d.getVar('TARGET_ARCH')
+
if 'vfpv4' in feat:
f.append("+vfp4")
elif 'vfpv4d16' in feat:
@@ -46,6 +48,9 @@ def llvm_features_from_tune(d):
if target_is_armv7(d):
f.append('+v7')
+ if 'armv8a' in feat and target_arch == 'arm':
+ f.append('+v8')
+
if ('armv6' in mach_overrides) or ('armv6' in feat):
f.append("+v6")
if 'armv5te' in feat:
@@ -63,7 +68,8 @@ def llvm_features_from_tune(d):
if 'thumb' in feat:
if d.getVar('ARM_THUMB_OPT') == "thumb":
- if target_is_armv7(d):
+ if target_is_armv7(d) or \
+ ('armv8a' in feat and target_arch == 'arm'):
f.append('+thumb2')
f.append("+thumb-mode")
@@ -302,7 +308,16 @@ def arch_to_rust_target_arch(arch):
return arch
# Convert a rust target string to a llvm-compatible triplet
-def rust_sys_to_llvm_target(sys):
+def rust_sys_to_llvm_target(sys, d):
+ # For AArch32 ARMv8-A, RUST_TARGET_SYS stays "arm-..." because "armv8a" is
not a
+ # valid Rust target architecture. Rewrite llvm-target to "armv8a-..." here
so
+ # ParseARMTriple adds "+armv8-a" and transitively sets HasV4TOps in the
+ # MCSubtargetInfo used for module-level inline asm parsing, making
hasThumb()
+ # return true for .thumb directives.
+ if sys.startswith('arm-') and \
+ 'armv8a' in (d.getVar('TUNE_FEATURES') or '').split() and \
+ d.getVar('TARGET_ARCH') == 'arm':
+ return 'armv8a-' + sys[4:]
return sys
# generates our target CPU value
@@ -382,7 +397,7 @@ def rust_gen_target(d, thing, wd, arch):
# build tspec
tspec = {}
- tspec['llvm-target'] = rust_sys_to_llvm_target(rustsys)
+ tspec['llvm-target'] = rust_sys_to_llvm_target(rustsys, d)
tspec['data-layout'] = d.getVarFlag('DATA_LAYOUT', arch_abi)
if tspec['data-layout'] is None:
bb.fatal("No rust target defined for %s" % arch_abi)
--
2.43.0
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